petroleum analysis by atmospheric pressure photoionization fourier transform ion cyclotron

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Electronic Theses, Treatises and Dissertations The Graduate School

2007

Petroleum Analysis by AtmosphericPressure Photoionization FourierTransform Ion Cyclotron Resonance MassSpectrometryJeremiah Michael Purcell

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THE FLORIDA STATE UNIVERSITY

COLLEGE OF ARTS AND SCIENCES

PETROLEUM ANALYSIS BY ATMOSPHERIC PRESSURE

PHOTOIONIZATION FOURIER TRANSFORM ION

CYCLOTRON RESONANCE MASS SPECTROMETRY

By

JEREMIAH MICHAEL PURCELL

A Dissertation submitted to the Department of Chemistry and Biochemistry

in partial fulfillment of the requirements for the degree of

Doctor of Philosophy

Degree Awarded: Spring Semester, 2007

Copyright © 2007 Jeremiah Michael Purcell

All Rights Reserved

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The members of the Committee approve the Dissertation of Jeremiah M. Purcell defended on March 19, 2007.

Alan Marshall Professor Directing Dissertation

Vincent Salters Outside Committee Member

William Cooper Committee Member

Timothy Logan Committee Member

Ryan Rodgers Committee Member

Christopher Hendrickson Committee Member

Approved:

Joseph Schlenoff, Interim Chair, Department of Chemistry and Biochemistry

Joseph Travis, Dean, College of Arts and Sciences The Office of Graduate Studies has verified and approved the above named committee members.

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To

Shannon Elodie Willkens Hand-in-Hand Together

and

Mom and Dad

John Edward Purcell Mary Ann Hobbs Purcell

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ACKNOWLEDGEMENTS

Foremost, I owe a debt of gratitude to Alan Marshall, my advising

professor. I will always be humbled by Professor Marshall’s breadth of

knowledge and his unique ability to communicate exquisitely either

verbally or written. Alan, my hat is off, thanks.

I thank Chris Hendrickson and Ryan Rodgers. I was fortunate to

be exposed to leading scientist in the field of mass spectrometry. Chris

and Ryan individually are accomplished analytical chemist but the

combination of their abilities is unparalleled. Thanks Chris and Ryan.

I want to thank Mark Emmett. In my excursion to find

buckybowls, I had a steep learning curve in the field of liquid

chromatography. Mark’s vast knowledge was irreplaceable. A big Texas

thank you Mark.

I thank John Quinn. There is always someone in a group (and in

the US Air Force) who is the go-to person to find the answer. I can’t

count how many times John pointed this grad student in the right

direction. Countless thanks John.

I want to also thank all the Marshall group members, past and

present. It has been a privilege to work with you and I look forward to

future endeavors.

I want to thank all my family. A special thanks to Shannon,

Emalee and Sarah. To Emalee and Sarah, two wonderful daughters who I

know will achieve great things, I love you. To Shannon, the love of my

life and a life companion, I love you completely.

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TABLE OF CONTENTS

LIST OF TABLES............................................................................ IX

LIST OF FIGURES ........................................................................... X

ABSTRACT..................................................................................XVII

CHAPTER 1. INTRODUCTION.......................................................... 1

Fourier Transform Ion Cyclotron Resonance Mass Spectrometry .... 1

Key Scientific Events .......................................................................... 1

Ion Cyclotron Motion Theory .............................................................. 2

Perturbation of Cyclotron Motion........................................................ 3

9.4 Tesla FT-ICR Mass Spectrometer at the National High Magnetic Field Laboratory (NHMFL)................................................................... 4

Atmospheric Pressure Photoionization ........................................... 6

Photon Ionization ............................................................................... 6

Photoionization Pathways................................................................... 7

Thermo Fisher Scientific APPI Source ................................................. 9

Speciation of Non-polar Petroleum Compounds............................. 11

Kendrick Data Analysis and Double Bond Equivalents Calculations12

CHAPTER 2. ATMOSPHERIC PRESSURE PHOTOIONIZATION FOURIER TRANSFORM ION CYCLOTRON RESONANCE MASS SPECTROMETRY FOR COMPLEX MIXTURE ANALYSIS.................. 14

Summary...................................................................................... 14

Introduction ................................................................................. 14

Experimental Methods.................................................................. 16

Solvents and Compounds................................................................. 16

Crude Oil ......................................................................................... 17

Results And Discussion................................................................. 17

Model Compounds ........................................................................... 18

The Nitrogen Rule ............................................................................ 20

Complex Mixture Analysis ................................................................ 22

Negative Ions.................................................................................... 24

Mass accuracy ................................................................................. 27

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Conclusions.................................................................................. 30

CHAPTER 3. COMPARISON OF ATMOSPHERIC PRESSURE PHOTOIONIZATION AND ELECTROSPRAY IONIZATION OF CRUDE OIL NITROGEN CONTAINING AROMATICS BY FOURIER TRANSFORM ION CYCLOTRON RESONANCE MASS SPECTROMETRY................. 31

Summary...................................................................................... 31

Introduction ................................................................................. 31


South American Crude Oil................................................................ 33

Nitrogen Class Compounds .............................................................. 33

ESI Experimental Conditions............................................................ 34

Results and Discussion ................................................................. 34

Nitrogen Compounds........................................................................ 34

Nitrogen Class Speciation................................................................. 36

Ion Fragmentation............................................................................ 41

Conclusions.................................................................................. 45

CHAPTER 4. ATMOSPHERIC PRESSURE PHOTOIONIZATION PROTON TRANSFER FOR COMPLEX ORGANIC MIXTURES INVESTIGATED BY FOURIER TRANSFORM ION CYCLOTRON RESONANCE MASS SPECTROMETRY ............................................ 48

Summary...................................................................................... 48

Introduction ................................................................................. 48


Solvents and Compounds................................................................. 50

Crude Oil ......................................................................................... 50


Nitrogen Class Compounds .............................................................. 51

Bitumen Distillation Cuts................................................................. 54

Deuteration versus Protonation ........................................................ 56

Negative and Positive Ion Class Distribution Comparison ................. 59

Conclusions.................................................................................. 59

CHAPTER 5. SULFUR SPECIATION OF PETROLEUM BY ATMOSPHERIC PRESSURE PHOTOIONIZATION FOURIER

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TRANSFORM ION CYCLOTRON RESONANCE MASS SPECTROMETRY.................................................................................................... 63

Summary...................................................................................... 63

Introduction ................................................................................. 63


Middle East Crude Oil ...................................................................... 65


Middle East Crude Analysis.............................................................. 66

Conclusions.................................................................................. 72

CHAPTER 6. LIMITATIONS OF AROMATIC SULFUR CHEMICAL DERIVATIZATION ANALYSIS OF PETROLEUM BY ESI AND APPI FOURIER TRANSFORM ION CYCLOTRON RESONANCE MASS SPECTROMETRY .......................................................................... 73

Summary...................................................................................... 73

Introduction ................................................................................. 74


Vacuum Bottom Residue.................................................................. 76

SARA Fractionation.......................................................................... 77

CHNOS Analysis .............................................................................. 78


APPI FT-ICR MS ............................................................................... 78

Raw Vacuum Bottom Residue .......................................................... 79

Raw Methylated Vacuum Bottom Residue ........................................ 82

Saturate and Aromatic Fraction of the Vacuum Bottom Residue....... 85

Conclusions.................................................................................. 90

CHAPTER 7. CONCLUSIONS AND APPI FT-ICR MS APPLICATION AND COLLABORATION WITH THE INSTITUTE OF PETROLEUM AT FRANCE; A REAL WORLD APPLICATION ....................................... 92

Assessment of APPI Technology.................................................... 92

APPI FT-ICR MS Applied to Current Petrochemical Challenges...... 94

Introduction..................................................................................... 94

Residue Sample Overview................................................................. 96

Asphaltene Analysis ......................................................................... 99

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Overall Conclusion ..........................................................................108

APPENDIX A. CARBON CLUSTER STRUCTURAL CHARACTERIZATION BY GAS PHASE ION-MOLECULE REACTION IN AN FT-ICR MASS SPECTROMETER ..............................................109

Fullerene Introduction.................................................................109

Instrumentation ..........................................................................110

Cluster Source ................................................................................110

Cluster Source Coupled to Existing 9.4 T FT-ICR Mass Spectrometer.......................................................................................................113

Retarding Potential Study................................................................116

Cluster Spectra............................................................................116

Mass Range.....................................................................................116

In-Cell Gas-Phase Ion-Molecule Reactions .......................................119

Conclusions.................................................................................125

APPENDIX B. REACTION OF HYDROGEN GAS WITH C60 AT ELEVATED PRESSURE AND TEMPERATURE: HYDROGENATION AND CAGE FRAGMENTATION ..............................................................127

Summary.....................................................................................127

Introduction ................................................................................127

Experimental Section ..................................................................129

Results and Discussion ................................................................130

APPI FT-ICR MS of Hydrogenated Samples ......................................130

APPI versus FD FT-ICR MS..............................................................137

Low Mass Ions ................................................................................139

Elemental Composition of Hydrofullerene Mixtures..........................141

Conclusion ..................................................................................142

REFERENCES ..............................................................................144

BIOGRAPHICAL SKETCH .............................................................155

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LIST OF TABLES

Table 1.1. Example of a Crude Oil Homologous Series Categorized by Class, DBE and Carbon Number Distribution. DBE and Molecular Formulas Correspond to the Ion as Opposed to the Neutral Compound. ............................................ 13

Table 2.1 Elemental Compositions Assigned to Peaks in the Negative-ion APPI FT-

ICR Mass Spectral Segment Shown in Figure 2.5. All elemental compositions are for the deprotonated molecule, (M-H)-. Note that measured and calculated masses are uniformly identical to six places, and differ only at the sub-ppm level (shown in red)..................................................................................... 26

Table 3.1. List of DBE 9 positive-ion N1-class APPI species (M+�) and the DBE 9.5

negative–ion N1-class ESI species (M-H)-. Each molecular formula (and the DBE value computed from it (Eq. 1.19)) is for the stated ion, not its neutral precursor.................................................................................................... 43

Table 4.1. Positive-ion APPI FT-ICR MS ion relative abundances for the five

aromatic nitrogen compounds of Figure 4.1. Parenthetical values show the percentages of M+�, [M + H]+, and [M + D]+ for each compound. ..................... 54

Table 7.1. Total Elemental Peak Assignment and Root-Mean-Square Mass Error

(mass error, difference between experimentally measured mass and the exact mass corresponding to the elemental composition assigned to that mass spectral peak). The asphaltene alpha-numeric designators correspond to Figure 7.1................................................................................................... 97

Table A.1. Spectra Instrument Parameters ....................................................... 117

Table A.2. Percent Relative Abundance of Cluster Reaction Products .............. 124

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LIST OF FIGURES Figure 1.1 9.4 Tesla FT-ICR mass spectrometer. Graphical presentation of the

differentially pumped vacuum chambers and ion optics. Differential pumping achieves ultra low pressure (10-10 Torr) at the ICR cell. At atmosphere pressure, ions are introduced through a heated metal capillary to the first radio frequency (rf) octopole ion guide for external accumulation, transferred to the middle octopole (collisionally cooled with helium) and then pulsed to the ICR cell. ................................................................................................. 5

Figure 1.2. Two-dimensional layout of the APPI ion source. For simplicity, the

vacuum UV lamp is drawn along the z axis with the heated metal capillary. In practice, the lamp is along the x axis so that the three assemblies are mutually orthogonal. .................................................................................. 10

Figure 2.1. Class distribution from an APPI positive-ion FT-ICR mass spectrum of

Middle East crude oil. ................................................................................. 19

Figure 2.2. APPI positive-ion FT-ICR mass spectra of 30 µM naphtho[2,3-a]pyrene

in toluene (top) and hexanes (bottom). Top: The insets show the two kinds of ions formed in the APPI source region; protonated molecules and radical molecular cations. Nine acquisitions were summed with an external ion accumulation of 5 seconds each, resulting in a SNR of 2300. Bottom: The insets show the reduction in formation of the protonated molecule in the absence of a dopant. Nine acquisitions were summed with an external ion accumulation of 10 seconds each................................................................ 21

Figure 2.3. APPI FT-ICR mass scale-expanded segment for a South American crude

oil. The mass doublets document the requirement for ultrahigh mass resolving power with an APPI source for complex mixture analysis. The 3.4 mDa mass doublet corresponds to species differing by C3 vs. SH4 and the 4.5 mDa mass doublet to 12CH vs. 13C. Two hundred acquisitions were summed with an ion accumulation of 3 seconds each. Starred peaks were assigned to elemental compositions not shown in the Figure. ....................................... 23

Figure 2.4. APPI FT-ICR mass scale-expanded segment of a high-sulfur Middle

East crude oil, showing a very close 1.1 mDa mass doublet, 12C4 vs. SH313C. Two hundred acquisitions were summed with an external ion accumulation of 5 seconds each. Starred peaks were assigned to elemental compositions not shown in the Figure.................................................................................... 25

Figure 2.5. Negative ion APPI FT-ICR broadband mass spectrum of a South

American crude oil. Bottom: Across a 400 Dalton mass window, 12,449 unique elemental compositions (a new record for a single mass spectrum) were assigned (> 99% deprotonated molecules), based on an average mass resolving power of ~400,000 and an rms mass accuracy of 260 parts per billon. Top: At a S/N ratio > 8 σ of baseline noise, there are 63 spectral peaks of nominal mass 377 Da of which unique elemental compositions could be assigned to 62 (see Table 2.1). .................................................................... 28

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Figure 2.6. APPI FT-ICR mass spectral peak magnitude vs. mass error (measured mass minus the exact mass for the assigned chemical formula) for the elemental compositions assigned to 12,449 spectral peaks from Figure 2.5. Ninety percent of the peaks exhibit less than 500 ppb mass error. As predicted,53 mass accuracy increases with increasing mass spectral S/N ratio. 29

Figure 2.7. Mass error distribution for the 12,449 spectral peaks from Figure

2.5. Each bar represents the number of assigned masses within a 50 ppb "bin" mass error range. At half-maximum height, the errors span a range of ±200 ppb. ................................................................................................... 29

Figure 3.1. ESI and APPI ionization pathways for acridine and carbazole. For

ESI, negative-ion and positive-ion spectra would be necessary to detect both species. However, both compounds yield APPI positive ions. Double bond equivalents (DBE) are calculated from Eq. 1.19 for each ion. ....................... 35

Figure 3.2. Nitrogen class compounds. Carbazole and

7H-dibenzo[c,g]carbazole are pyrrolic (acidic), whereas acridine and 7,9-dimethylbenz[c]acridine are pyridinic (basic) species. Ellipticine, with two nitrogen heteroatoms, has both pyrrolic and pyridinic moieties. .......... 35

Figure 3.3. Negative-ion and positive-ion ESI FT-ICR mass spectra of

representative nitrogen-class compounds. For both spectra, an equimolar solution was electrosprayed. The pyrrolic species were ionized by negative-ion ESI and the pyridinic species by positive-ion ESI. Ellipticine was detected in both negative-ion and positive-ion spectra................................ 37

Figure 3.4. Negative-ion and positive-ion APPI spectra of representative nitrogen-

class compounds. For both spectra, an equimolar solution was infused into the APPI source. The pyrrolic species were detected in the negative-ion APPI spectrum, and all five compounds were detected in the positive-ion APPI spectrum. ................................................................................................... 38

Figure 3.5. Positive-ion APPI FT-ICR broadband mass spectrum of a South

American crude oil. Both radical molecular ions and protonated compounds are formed in the APPI source. The mass scale-expanded inset shows two common spectral peak doublets for APPI. Naphtho[2,3-a]pyrene was added to the petroleum sample to test for possible fragmentation. No fragment ions were observed............................................................................................. 40

Figure 3.6. ESI (positive-ion and negative-ion) and APPI (positive-ion) DBE

distributions for the N1 class from the petroleum sample. The ion DBE is calculated from Equation 1.19. The total relative ion abundance for each DBE is plotted on the y-axis. For ESI, protonation or deprotonation yield ions of half-integer DBE values. For APPI, radical molecular ions yield integer DBE values. Note that positive-ion APPI can distinguish pyridinic (M+H)+ from pyrrolic (M+�) nitrogen ions based on their respective integer and half-integer DBE values............................................................................... 42

Figure 3.7. Schematic representation (not to scale) of the Heated Metal Capillary

(HMC), tube lens, and skimmer housed in the first differentially pumped stage of the mass spectrometer. Ions are transferred through the HMC and are focused by the tube lens before reaching the skimmer conductance limit. The gas dynamics in the tube lens/skimmer region can cause fragmentation

xii

but fragmentation can be negated by appropriate pressure and voltage adjustments (see text)................................................................................. 44

Figure 3.8. Positive-ion APPI FT-ICR mass spectra of naphtho[2,3-a]pyrene

(C24H14, neutral monoisotopic mass, 302.110 Da) for various choices of tube lens voltage and skimmer region pressure. Fragmentation is evident at higher tube lens potential and/or lower pressure. At a tube lens potential of 200 V DC and a skimmer region pressure of 2.1 Torr, no fragmentation was observed..................................................................................................... 46

Figure 4.1. Five aromatic nitrogen compounds chosen to model petroleum acidic

and/or basic compounds. Five-membered ring nitrogen structures are acidic and six membered ring nitrogen species are basic. ...................................... 51

Figure 4.2. Negative ion APPI FT-ICR mass spectrum of an equimolar solution of

the model compounds of Figure 4.1 in deuterated toluene. Only the acidic compounds containing a pyrrole ring are deprotonated to yield [M - H]- ions, none of which contained deuterium............................................................ 53

Figure 4.3. Positive ion APP FT-ICR mass spectrum of an equimolar solution of

the model compounds of Figure 4.1 in deuterated toluene. All five compounds yielded positive molecular (M+�) or quasimolecular ([M - H]-) ions. The compounds containing a six-membered pyridinic ring are sufficiently basic to readily protonate (or deuterate) (along with ~1% of radical molecular radical cations), whereas the more acidic compounds containing a five-membered pyrrolic ring form molecular radical cations, and <1% protonation (or deuteration). For the even-electron species, the extent of deuteration was ~15% for acridine (see the mass scale-expanded inset spectrum), ~10% for ellipticine, and ~14% for 7,9-dimethylbenz[c]acridine. Also, at nominal mass 268 (right mass scale-expanded inset), 7H-dibenzo[c,g]carbazole exhibits slight hydrogen-deuterium exchange. ......................................................... 55

Figure 4.4. Heteroatom class distribution for a bitumen mid-range distillate

positive ions. Each class represents the relative ion abundance of species which contain the stated heteroatom(s) in the assigned molecular formula. The error bars are standard deviation computed from 3 separate sample preparations and analysis. .......................................................................... 57

Figure 4.5. Broadband APPI FT-ICR mass spectra of a bitumen mid-range

distillate. The positive- and negative-ion spectra were collected without source interruption and with appropriate instrument polarity changes. Although APPI produces both molecular radical cations (M+�) as well as [M - H]- and [M + H]+ ions, the N1 class positive-ion mass spectrum is dominated (~97%) by protonated compounds. .............................................................. 58

Figure 4.6. Positive-ion APPI FT-ICR mass scale-expanded segment of a bitumen

mid-range distillate in deuterated toluene. This figure emphasizes the ultrahigh resolving power required to resolve the deuterated species in complex petroleum mixtures. ..................................................................... 60

Figure 4.7. Heteroatom class distribution for the positive and negative ions from

a bitumen mid-range distillate. Generic structures are shown for the most abundant positive and negative species. DBE is the number of rings plus double bonds, and is calculated from Eq. 4.1. Because only ~5% of the even-electron N1 class ions contain deuterium, the acidic neutrals in the original

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sample are likely proton donors to form the even-electron species from basic neutrals...................................................................................................... 61

Figure 5.1. Broadband positive APPI FT-ICR mass spectra of the whole crude

and its SARA fractions. The samples were analyzed at the same concentration and experimental conditions. ............................................... 67

Figure 5.2. Summed relative ion abundance for heteroatom classes in the whole

crude. Middle East crude oils have a high sulfur content. The graph includes those heteroatom classes above 1% relative abundance. Eight of the eleven classes contain one or more sulfur atoms.................................................... 68

Figure 5.3. Summed relative ion abundance class graphs for the SARA fractions.

The saturate, aromatic, and asphaltene fractions show sulfur species most abundant. For the resins, more polar heteroatom classes are dominant...... 70

Figure 5.4. Three-dimensional relative abundance contoured DBE versus carbon

number plot for selected heteroatom classes of the whole crude and its SARA fractions. Carbon number is represented on the x-axis and double bond equivalents (equation 1.19) on the y-axis. The z-axis is color scaled to relative ion abundance. All plots are scaled equally.................................... 71

Figure 6.1. Heteroatom class distribution for the raw vacuum bottom residue

(not methylated). All classes ionized by ESI and APPI above 1 % relative abundance are represented. The non-polar classes, e.g., S1, S2 and HC (hydrocarbon), were not detected by ESI. APPI analysis detected both the polar and non-polar species. ....................................................................... 80

Figure 6.2. Iso-abundant contoured DBE versus carbon number images for

heteroatom species of the raw vacuum bottom residue. Relative ion abundance within the class is color scaled in the z-axis. The ESI and APPI N1S1 classes have similar carbon number distributions. However, the DBE distribution for the APPI N1S1 image extends to higher DBE. The non-polar S1 species was not detected by ESI.................................................................. 81

Figure 6.3. Heteroatom class distribution for the raw methylated vacuum bottom

residue. All classes ionized by ESI and APPI above 1 % relative abundance are represented. The ESI distribution exhibits a remarkable change in highest relative abundance to the S1 class. The S2, HC and O1 classes are also detected by ESI in the methylated sample. The APPI heteroatom class distribution is similar to Figure 6.1. ........................................................... 83

Figure 6.4. Iso-abundant contoured DBE versus carbon number images for

heteroatom species of the raw methylated vacuum bottom residue. Relative ion abundance within the class is color scaled in the z-axis. The N1S1 images are similar to the images produced from the unmethylated sample (Figure 6.2). However, the S1 class images differ dramatically between ESI and APPI. The low DBE species in the ESI S1 image are absent in the APPI image. ...... 84

Figure 6.5. APPI analyzed heteroatom class distribution for the saturates,

aromatics and a solution of saturates and aromatics fractionated from the vacuum bottom residue. The saturates and aromatic solution was an equal molar concentration prepared by mixing equal volumes of equal mass/volume solutions. All classes above 1 % relative abundance are represented........... 86

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Figure 6.6. S1 DBE distribution of the saturates, aromatics, and the saturate/aromatics solutions. The calculated DBE values (equation 1.19) are for the cation (not the neutral species). Therefore, non-integer values are possible for protonated compounds [M + H]+. The analysis of the combined saturates and aromatics (equal weight/concentration) show a broad distribution which encompasses both the individual saturate and aromatic DBE distributions. ...................................................................................... 88

Figure 6.7. Iso-abundant contoured image for the S1 class of the saturates,

aromatics and saturates/aromatics solutions. Relative ion abundance within the class is color scaled in the z-axis. The same trend seen in the DBE distribution graph (Figure 6.7) is represented in the images. The lower DBE species are found in the saturate fraction, higher DBE species in the aromatic fraction, and a combination of the individual DBE distribution values in the combined image. ........................................................................................ 89

Figure 7.1. Residue hydroconversion scheme. Sample designations A1, A2, A11

and A22 reflect hydroconversion in fixed bed conditions. Sample A1 and A2 were reacted at different temperature (hydrodemetalization) and further reacted to produce A11 and A22 (hydrodesulfurization). Samples B1, B2, and B3 were obtained in ebullated bed conditions at different increasing residence times.......................................................................................................... 96

Figure 7.2. Broadband APPI FT-ICR mass spectrum of the IFP aromatic sample

(bottom). Zoom insets (top) identify [C30H18S3 + H]+ (64 % relative abundance), [C29H18S313C1 + H]+ (22 % relative abundance, and [C29H18S213C134S1 +H]+ (3 % relative abundance). ................................................................................... 98

Figure 7.3. Heteroatom class distribution for the IFP asphaltene sample. Forty

heteroatom classes were assigned. For classes above 1 % relative abundance (top), 15 of the 17 classes contain one or more sulfur atoms. Also note the hydrocarbon class (HC) is present in low abundance.................................. 100

Figure 7.4. Class distribution for samples A1 and A2 (Figure 7.1). Each sample is

normalized to the most abundant class within its class distribution, i.e., they are mutually exclusive. Sample A1 was reacted at 380 °C and sample A2 at 400 °C. ..................................................................................................... 101

Figure 7.5. Iso-abundant contoured DBE versus carbon number plot of the feed

asphaltene and A1 sample; sulfur and hydrocarbon classes. Relative ion abundance is color scaled in the z-axis. A dashed reference line is added to enhance graph-to-graph comparison. ........................................................ 103

Figure 7.6. Iso-abundant contoured DBE versus carbon number plot of the feed

asphaltene and A2 sample; sulfur and hydrocarbon classes. Relative ion abundance is color scaled in the z-axis. A dashed reference line is added to enhance graph-to-graph comparison. ........................................................ 103

Figure 7.7. Heteroatom class distribution of the final reaction products (A11 and

A22). ........................................................................................................ 104

Figure 7.8. Iso-abundant contoured DBE versus Carbon number plot for the

hydrocarbon classes of A11 and A22. A22 shows an increase in aromaticity (increase in carbon number-to-DBE ratio).................................................. 105

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Figure 7.9. Class distribution for samples B1, B2 and B3. With increasing hydroconversion time, there is a corresponding reduction in sulfur species with an increase in hydrocarbon species. .................................................. 106

Figure 7.10. Iso-abundant carbon number versus DBE contoured plots for the

hydrocarbon classes of samples B1, B2 and B3. The plots display an overall migration of the most abundant species toward greater aromaticity. Structures a, b, and c (bottom) represent the predicted stable structures which correspond to elemental species hot spots for sample B3................ 107

Figure A.1. Diagram of the 5.3 Split-pair FT-ICR mass spectrometer (unshielded

magnet) in its original configuration at Lucent Technologies (not to scale). The eight inch bore of the magnet is vacuum sealed and was designed with four access ports which allows trapped ion interrogation within the ICR cell................................................................................................................. 110

Figure A.2. Ion optics lens stack. This lens stack is mounted to the source block.

The first electrode (labeled source potential) is physically connected to the source block and, therefore at the same potential as the source. Note the mechanical 10° offset of the final two electrodes. ..................................... 111

Figure A.3. Ion optics and differential pumping diagram. The zoom inset details

the source block and static potential optics. Conductance limits 2 and 3 are held at trapping potentials during external ion accumulation. .................. 112

Figure A.4. Interface octopole ion guide. The octopole operated at 1.4 - 2.6 MHz

and ~300 volts peak-peak amplitude with a -30 V DC offset. The overall length was ~27 inches. ............................................................................. 113

Figure A.5. Retarding potential profile. Total ion current (y-axis) is measured on

accumulator octopole rods and CL2 potential (x-axis) is varied. CL2 is the accumulator entrance lens. Source, extraction, and CL1 potentials are plotted to investigate ion kinetic energy. ................................................. 115

Figure A.6. Carbon cluster broadband FT-ICR mass spectrum. Spectra was

collected on the initial day of instrument operation. Additional instrument parameter are reported in Table A.1.......................................................... 117

Figure A.7. Broadband carbon cluster mass spectrum (2600 ≤ m/z ≤ 4600).

Instrument parameters favored accumulation and transfer of high m/z ions. The zoom inset shows the C278 monoisotopic peak and its isotopic variants................................................................................................................. 118

Figure A.8. Low mass carbon cluster mass spectrum. Although this is a single

acquisition, 400 laser pulses were required to accumulate this ion population................................................................................................................. 119

Figure A.9. SWIFT isolated C28 with a 30 msec NO pulse gas event. The [C28NO]+�

spectral peak magnitude is 13% relative abundance. The loss of C2 ([C26]+�) spectral peak is 1 % relative abundance.................................................... 120

Figure A.10. Theoretical stable structure of fullerene C28. The four red carbon

atoms are at the vertices of triplet pentagons. In this isomer form, the red atoms have sp3 orbitals with a lone electron. ............................................ 121

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Figure A.11. Double resonance SWIFT isolation of C28 with NO pulse gas. Experimental sequence spectrum A (top): SWIFT isolation C28, 30 msec NO pulse gas event, SWIFT isolation C28, 30 msec NO pulse gas event. Spectrum B (bottom) was recorded immediately (2 minutes) after spectrum A without NO pulse gas............................................................................................. 122

Figure A.12. Reaction of carbon cluster C50 with NO gas. The cluster (spectral

peak at 600 m/z) was SWIFT isolated and reacted with a 30 msec NO gas pulse. The reaction product [C50NO]+� was detected at 3 % RA. The reaction also showed a strong loss of C2. ................................................................ 124

Figure B.1. APPI FT-ICR mass spectra of C60 samples with different degrees of

hydrogenation. ......................................................................................... 131

Figure B.2. APPI FT-ICR MS from the 3.8 wt % sample. The most abundant ions

are assigned. ............................................................................................ 133

Figure B.3. APPI FT-ICR mass spectra from the samples with maximum

hydrogenation (5.0 wt % (top) and 5.3 wt % (bottom)). .............................. 134

Figure B.4. Scale-expanded m/z segment, 739-740 Da, for samples with different

hydrogen contents.................................................................................... 135

Figure B.5. Carbon and hydrogen compositions obtained from APPI FT-ICR mass

spectra (for mass spectral peaks with S/N > 7). ......................................... 136

Figure B.6. FT-ICR mass spectra 5.0 wt % samples: (top) FD; (bottom) APPI. ... 138

Figure B.7. APPI FT-ICR MS of the 5.3 wt % sample under conditions that favor

higher abundance of low-mass ions. Filled triangles denote higher-abundance species. .................................................................................................... 140

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ABSTRACT

Petroleum and petroleum products are an integral part of today’s

society. Although petroleum is projected to be the dominant energy

source for the next fifty years, the depletion of light sweet crude oil

reserves has led to the refinement of heavier feedstocks. Heavier

petroleum feedstocks contain higher weight percent sulfur-, nitrogen-

and oxygen-containing species. Not only is the combustion of these

species harmful to the environment, they can also poison catalytic and

hydrotreatment refining equipment. The United States Environmental

Protection agency has limited allowable heteroatom weight percents in

petroleum products. Moreover, sulfur is the third most abundant

element in petroleum and has been regulated to parts-per-million levels

and further reduction slated for the year 2010.

To meet the more stringent environmental regulations, refineries

are facing major challenges. Mass spectrometry has proven to be a

valuable tool for the molecular speciation of petroleum. Notably,

electrospray ionization Fourier transform ion cyclotron resonance (FT-

ICR) mass spectrometry has proven invaluable for the speciation of the

polar compounds in crude oil. This analysis has added to the

understanding of specific refinery problems, e.g., solid deposition and

flocculation. However, hydrocarbons and non-polar sulfur species are

not accessible by ESI mass spectrometry. Atmospheric Pressure

PhotoIonization (APPI) can produce ions from non-polar (and polar)

species. Chapter 1 is a brief discussion of basic ICR principles, APPI

pathways, instrumentation and data analysis.

In Chapter 2, I describe an APPI source coupled to the

in-house-built 9.4 Tesla Fourier transform ion cyclotron resonance (FT-

ICR) mass spectrometer at the National High Magnetic Field Laboratory

(NHMFL) in Tallahassee, Florida. This chapter highlights the complexity

xviii

of crude oil analysis with an APPI source. The possibility of forming two

ion types (protonated compounds and radical molecular ions) from one

compound complicates an already complex spectrum. Model compound

spectra demonstrate the necessity of ultra-high resolution mass

spectrometry to resolve common mass doublets (3.4 mDa, the mass

difference between C3 vs. SH4; 4.5 mDa, the mass difference between

12CH and 13C) found in petroleum spectra. Also, this report establishes

the highest number of resolved (and assigned elemental formulas)

spectral peaks (>12,000 peaks in a single mass spectrum and up to 63

peaks of the same nominal mass) in one mass spectrum.

Although APPI is considered to be a soft ionization technique, the

analyte is nebulized and heated before ion formation. On the other

hand, ESI is a well established soft ionization process. Therefore, in

Chapter 3, I compare ESI and APPI data from the same crude oil and

also pyridinic and pyrrolic nitrogen model compounds. The chapter

defines instrument parameters which can cause fragmentation (loss of

H2) and parameters which do not. ESI and APPI crude oil spectra yield

the same elemental species, providing evidence that APPI can produce an

ion population without fragmentation.

A dopant (proton donor) is advantageous for APPI mass

spectrometry because proton transfer reactions are enhanced. For

simple mixture analysis, the proton donor is predominantly the dopant.

However, for complex mixture analysis (crude oil), the solution matrix

can contain species which could also participate in proton transfer

reactions. In Chapter 4, I investigate the proton transfer reaction for a

Canadian bitumen petroleum in deuterated toluene (C7D8). Nitrogen

class compounds are also analyzed in deuterated toluene. The dopant

percent contribution to the even-electron ions (protonated and

deuterated compounds) of the petroleum is ~5 %. The nitrogen model

compounds exhibited a similar trend.

xix

Petrochemical analysis commonly employs the saturates-aromatic-

resins-asphaltenes (SARA) separation method. In Chapter 5, the sulfur

containing compounds of a Middle East crude oil are speciated. The

crude oil is additionally fractionated by the SARA method and its

fractions are analyzed by APPI FT-ICR mass spectrometry. Molecular

species from the whole crude oil and its fractions are compared to

ascertain differences and similarities between sulfur species in the

fractions.

Non-polar sulfur species are not efficiently ionized by ESI.

However, derivatization chemistry can methylate polycyclic aromatic

sulfur species and form cations in solution with subsequent analysis by

ESI mass spectrometry. In Chapter 6, the derivatized and non-

derivatized samples of a petroleum vacuum bottom residue (the highest

boiling point fraction of petroleum and hence, the most complex

heteroatom content) are analyzed by ESI and APPI. Significant

differences in the double bond equivalent values (DBE, value equal to the

number of rings plus double bonds in the molecular structure calculated

from the elemental formula) between the ESI and APPI analyzed sulfur

species are identified. Furthermore, this report provides data that

probes APPI ionization efficiency.

Chapter 7 is a synopsis of the APPI technology applied to

petroleum analysis. The chapter also includes a real world application of

APPI FT-ICR mass spectrometry. The Institute of Petroleum at France

(IFP) is interested in the development of new hydroconversion processes

to upgrade vacuum bottom residue to more useful petroleum products.

A substantial fraction of vacuum bottom residue is the asphaltenes; the

most heteroatom-rich fraction in petroleum. The chapter presents

molecular speciation from intermediate stages of a hydroconversion

process; a first step in hydroconversion catalytic technology

improvement.

xx

A Ph.D. thesis may also include research outside the scope of the

primary dissertation research to achieve a broader understanding of the

sciences. Appendix A describes the ongoing construction and adaptation

of an ion cluster source to an existing FT-ICR mass spectrometer. The

primary investigator is Professor Harry Kroto, Nobel prize laureate for the

discovery of fullerenes. Fullerenes are closed cage molecules consisting

of 12 pentagonal and several hexagonal rings. Fullerenes with 60 carbon

atoms or larger follow the isolated pentagon rule (IPR). Smaller

fullerenes (< 60 carbon atoms) consist of isomers with adjoined pentagon

rings. Perhaps one of the more interesting small fullerenes is C28. The

structure in part consist of four reactive carbons bonded in sp3 orbitals

located at the apex of triplet pentagons which form 4 tetrahedral vertices.

The research focuses on the formation of C28 by laser vaporization and

gas phase reaction products in the ICR cell.

In appendix B, the reaction products of C60 and hydrogen at high

temperature and pressure are resolved and identified. The product

species formed at elevated temperature and hydrogen pressure are

characterized by APPI FT-ICR mass spectrometry. Only the APPI

analysis (and Field Desorption, FD) were accomplished at Florida State

University and the first report (of three published reports) is presented.

1

CHAPTER 1. INTRODUCTION

Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Key Scientific Events

Fourier Transform Ion Cyclotron Resonance mass spectrometry is

an example of different aspects of science combining to form one

analytical technique, i.e., Fourier transforms, ion cyclotron resonance,

and mass spectrometry. Quoting Professor Alan Marshall from a 2001

Florida State University Alumni newsletter, “In research, I encourage my

students to maintain broad interests, because most new ideas don’t

come completely out of the blue; rather, they consist of connecting two

existing ideas and/or methods from initially different fields.”

Fourier, a brilliant mathematician, developed a theorem

subsequently named the Fourier transform.1 The theorem proved that a

waveform could be divided into the summation of sine and cosine

functions and then transformed into its frequency components. In

essence, changing the waveform from a time domain to a frequency

domain. Ion cyclotron resonance was introduced in 1932 as a method to

produce high energy ions to study collision processes.2 Mass

spectrometry was born from a need to characterize atomic isotope

abundance3 and was further advanced with the development of high

resolution instrumentation.4 Alan Marshall and Melvin Comisarow

developed the mass spectrometric method that combined Fourier

transforms, ion cyclotron resonance and mass spectrometry.5 Today, FT-

ICR mass spectrometry has evolved into the most powerful mass

determination technique primarily because of the inherent ultra-high

mass resolving power and ultra-high mass accuracy.6

2

Ion Cyclotron Motion Theory

The interaction of a charged particle (ion) with a spatially

homogenous magnetic field is the basis of ion cyclotron motion. An ion’s

path moving through a magnetic field is bent in a circular motion from

an applied force. The equation for the force is

0BvqonacceleratimassF ×=×= 1.1

where q, v, and B0 are ionic charge, velocity and magnet field strength

respectively. The cross product indicates the force is perpendicular to

the velocity and magnetic flux planes. The acceleration component of

uniform circular motion is

r

va

2

= 1.2

where v and r are velocity and radius. Substituting equation 1.2 into

equation 1.1

0

2

Bvqr

vm = 1.3

Also, angular velocity (ω) is equal to

vrorr

v== ωω 1.4

Therefore, substituting equation 1.4 into 1.3 and simplifying

3

m

Bq0=ω (S.I. units) 1.5

and a more useful form

Zu

B

m

BqZC

0

7

010553611.1

2

×==

πν

1.6

where vc is cyclotron frequency (Hz), u is in Dalton and Z is multiples of

elemental charge.

From equation 1.5 and 1.6, it is clear that the cyclotron frequency

is independent of the ion velocity. This precludes the need to focus the

translational energy of the ions for determining their mass/charge. It is

this which makes ion cyclotron resonance a valuable phenomenon for

mass spectrometry.7

Perturbation of Cyclotron Motion

The interaction of the ion with the magnetic field confines the ion

in an xy plane perpendicular to the magnetic flux plane (defined as the

z-axis). The trapping effect of the magnetic field, however, does not

confine ion motion along the z-axis. A static electric field potential

(trapping potential) is applied at the ends of the ICR trap to prevent ion

loss along the z-axis. The electric field perturbs the natural cyclotron

motion.

Furthermore, ions of the same mass–to-charge (m/z) ratio enter

the ICR trap with incoherent cyclotron motion and inconvenient ion

cyclotron radii. A broadband radio frequency (rf) excitation is applied to

two opposing plates in the ICR cell. The rf is applied as a frequency

4

sweep excitation (chirp) with a bandwidth equal to the ions of interest.

Ions with the same m/z ratio resonate with the applied chirp at their

cyclotron frequency and merge into coherent cyclotron orbits. Also, the

power absorbed from the chirp excites the ion packets into detectable ion

cyclotron radii.

Coulombic interactions between ions and the radial component of

the trapping potential perturb the ion cyclotron frequency. However, the

perturbation can be corrected with a mass calibration equation8

2v

B

v

A

z

m+= 1.7

where terms A and B are constants derived from two (or more) known

m/z values of calibrant ions. A calibration derived from calibrant ions

coexisting in the ICR cell works well because the calibrant ions and

analyte ions are equally perturbed.

9.4 Tesla FT-ICR Mass Spectrometer at the National High Magnetic Field Laboratory (NHMFL)

Figure 1.1 is a schematic drawing of the home built 9.4 Tesla ICR

mass spectrometer located at the NHMFL. This instrument was used to

acquire the FT-ICR mass spectral data for chapter 2-7 and appendix B.

The instrument is equipped with a passively shielded Oxford 9.4 Tesla

superconducting magnet.9, 10 The mass spectrometer is controlled by a

modular ICR data system.11, 12 Ions are produced at atmosphere

pressure (e.g., ESI or APPI) and traverse the heated metal capillary to the

first stage of vacuum pumping into a skimmer region. The skimmer

provides a conductance limit to the second stage of differential pressure

where the ions enter the first radio frequency (rf)-only octopole. In the

5

760 3×10-10

Front

Octopole

Middle

OctopoleQuadrupole

Transfer

OctopoleICR

Cell

Gas

Inlet

2 Torr3×10-3 5×10-6

~10-3 Torr

2×10-8 8×10-10

Heated Metal

Capillary

Figure 1.1 9.4 Tesla FT-ICR mass spectrometer. Graphical presentation of the differentially pumped vacuum chambers and ion optics. Differential pumping achieves ultra low pressure (10-10 Torr) at the ICR cell. At atmosphere pressure, ions are introduced through a heated metal capillary to the first radio frequency (rf) octopole ion guide for external accumulation, transferred to the middle octopole (collisionally cooled with helium) and then pulsed to the ICR cell.

6

first octopole, ions are accumulated (1-20 sec)13 before transfer through a

quadrupole (not operated in mass-resolving mode) into a second rf-only

octopole where they are collisionally cooled (10-20 ms) with helium

before transfer through an rf-only octopole to a 10-cm diameter, 30-cm-

long open cylindrical Penning ion trap. The octopole ion guides (1.6 mm

diameter titanium rods with a 4.8 mm i.d.) are typically operated

between 1.5 and 2.0 MHz and 190 < Vp-p < 240 V rf amplitude.

Broadband frequency-sweep excitation (~90-600 kHz at a sweep rate of

150 Hz/µsec and a 190 V peak-to-peak amplitude) applied to two

opposed electrodes accelerates the ions to a detectable cyclotron orbital

radius. Ion cyclotron resonant frequencies are detected from induced

current on two opposed detection electrodes of the ICR trap. Multiple

time-domain acquisitions are summed for each sample, Hanning-

apodized, and zero-filled once before fast Fourier transform and

magnitude calculation.6 Negative ion data is collected with similar

parameters and appropriate instrument polarity changes.

Atmospheric Pressure Photoionization

Photon Ionization

Photoionization can take place in the liquid or gas phase but at

different energy levels, e.g., water has an ionization potential of ~12.6 eV

in the gas phase but ~10.5 eV in the condensed phase.14, 15 An early

application of photoionization was detection of gas phase compounds. In

the early 1960's, photon sources were used as a detection method for gas

chromatography.16, 17 Analytes eluted from the GC column where

ionized, and an electrode collected the electrons to produce a

corresponding signal response. These early photoionization detectors

(PID) were not vacuum sealed and, thus, were problematic.

7

The detectors were maintained at low pressure with a vacuum

pump, were prone to coating problems from column bleed and were very

complex to operate.18 In 1976, Driscoll18 introduced a photoionization

detector with a sealed UV lamp which enabled the PID to be operated at

atmospheric pressure. The PID then became more functional for

chromatographic detection and began to replace the less sensitive Flame

Ionization Detector (FID).

More recently, photoionization (with a vacuum UV lamp) has

changed from a detector to an ionization source for mass spectrometers.

The first reports demonstrated photoionization coupled to a mass

spectrometer for the detection of hydrocarbons, ketones, alcohols and

amines.19, 20 Syage et al.,21, 22 demonstrated the application of

photoionization for pharmaceutical mass spectrometry methods. Syage’s

method primarily produced radical molecular ions [M]+� (odd electron

ions) through direct photoionization of the analyte. However, Bruins et

al, were the first to demonstrate dopant-assisted atmospheric pressure

photoionization (APPI).23 Dopant-assisted APPI increased ionization

efficiency through proton transfer reactions which produces even-

electron ions [M + H]+. Since the introduction of dopant-assisted APPI,

there has been a plethora of APPI mass spectrometry application

research in the biological24 and pharmaceutical25 sciences.

Photoionization Pathways

Direct photoionization ionization can be a one step process where

an electron is ejected when the absorbed photon energy is equal to or

higher than the first ionization energy (IE) of the molecule. Represented

as,

ionization: −•+ +→+ eAhvA 1.8

8

where A is the molecular species and hν represents photon energy

greater than the IE of A. However, there is an intermediate step where

the ionizable species is in an excited state and other pathways are

possible that result in neutral analyte26

ionization: −•+∗ +→→+ eAAhvA 1.9

photodissociation: BAAB +→∗ 1.10

radiative decay hvAA +→∗ 1.11

collisional quenching ∗∗ +→+ SASA 1.12

collisional quenching ∗∗ +→+ gasAgasA 1.13

electron capture gasAgasA +→+ −•+ 1.14

where S is the solvent and gas is any gas in the source region. There are

several pathways which do not result in charged species. At atmosphere

pressure and room temperature, the mean free path for a 10 Ǻ diameter

molecule is ~ 9 nano-meters. Therefore, the molecule would undergo ~ 2

X 1010 collisions/second. Statistically, the relative abundance of charged

species under these conditions is low.

Bruins et al. demonstrated dopant assisted APPI. A dopant can be

infused into the ionization source region in several ways. It can be mixed

with the solvent system directly, injected into the sample flow tube or

infused into the APPI source through an auxiliary port. A dopant adds to

the possible reaction pathways

protonated analyte [ ] [ ]+••+ ++−→+ HAHDAD 1.15

radical ion •+•+ +→+ ADAD 1.16

9

where D is the dopant and A is the analyte. If dopant ion molar

concentration far exceeds the analyte concentration, reactions 1.15 and

1.16 should prevail over charge quenching reactions.27 It is evident from

equations 1.15 and 1.16 that two ion types can form in the APPI source,

i.e., protonated compounds and radical molecular ions. Furthermore,

most APPI applications use a dopant. A common dopant is toluene, and

this is fortunate for APPI analysis of petroleum because toluene is also a

good solvent for petroleum products.

Thermo Fisher Scientific APPI Source

The APPI source was supplied by Thermo Fisher Scientific. The

vaporized analyte gas stream flows orthogonally to the mass

spectrometer inlet (heated metal capillary) and the Krypton vacuum UV

lamp (Figure 1.2) that produces 10 eV photons. The source is mounted

to a home-built adapter which interfaces the first differentially-pumped

stage of the 9.4 Tesla FT-ICR mass spectrometer through a heated metal

capillary. The heated metal capillary is .030 inches inside diameter and

resistively heated with direct current (3-4 amperes). The source-adapter

apparatus construction provides a closed area such that the nebulizer

gas (CO2) provides a slight positive pressure. A Harvard stainless steel

syringe (8 mL) and syringe pump are utilized to deliver solution to the

heated nebulizer of the APPI source. In the APPI source, solvent flow rate

is 50-100 µL/min, the nebulizer heater is operated at 250-350 °C with

carbon dioxide sheath gas at 50 p.s.i., and the auxiliary gas port is

plugged.

10

+

+++

Atmospheric Pressure milliTorr Pressure

+

Nebulizer

Heater

Vacuum UV Lamp

Heated Metal Capillary

Z

X

Y

-

-- --

APPI Source

Figure 1.2. Two-dimensional layout of the APPI ion source. For simplicity, the

vacuum UV lamp is drawn along the z axis with the heated metal capillary. In practice, the lamp is along the x axis so that the three assemblies are mutually orthogonal.

11

Speciation of Non-polar Petroleum Compounds

Current legislative trends for ultralow-sulfur fuels necessitate a

better understanding of the structure of sulfur species in petroleum to

facilitate the development of better hydrodesulfurization catalysts and

optimize processes conditions.28-30 Furthermore, with world petroleum

production shifting toward heavier heteroatom-rich crude oils, the

upgrading capacity of world refineries must increase to deal with the

large volume of heavy crudes.31 Hence, detailed sulfur speciation is of

paramount importance, from a refinery as well as environmental point of

view. Fourier transform ion cyclotron resonance (FT-ICR) mass

spectrometry significantly contributes to sulfur speciation through its

ability to correctly assign class, type and carbon number, providing

unambiguous molecular formulas for heteroatom-containing species

from mixtures as complex as unfractionated heavy petroleum.

Electrospray ionization mass spectrometry (ESI MS) has identified polar

compound classes from crude oil and its associated fractions.32, 33

However, sulfur compound classes (that are not sufficiently acidic or

basic, i.e., non-polar) and hydrocarbons are not efficiently ionized by ESI.

Structural elucidation of sulfur species by ESI may often require

chemical derivatization for enhanced detection. In contrast to ESI,

Atmospheric Pressure Photoionization (APPI) can efficiently ionize gas-

phase non-polar species21, 23 (and polar species) through direct photon

ionization or proton transfer (with a toluene dopant) and charge

exchange reactions. Hence, APPI coupled to FT-ICR mass spectrometry

can provide elemental composition of non-polar petroleum species to

help mitigate environmental and refinery problems.

12

Kendrick Data Analysis and Double Bond Equivalents Calculations

Because crude oil primarily consist of homologous series differing

only by nCH2 (n is a positive integer), it is convenient to convert the

experimental m/z (mass/charge) values to Kendrick mass.34, 35

( )01565.14

14×=z

mmassKendrick 1.17

The Kendrick masses of a homologous series differ by exactly 14 Da and

will have the same Kendrick Mass Defect (KMD).

( ) 1000massKendrick - mass nominal ×=KMD 1.18

The data set can then be sort by KMD in an Excel spreadsheet to

enhance assignment of elemental composition of a homologous series.

Furthermore, each homologous series can be categorized by class,

double bond equivalents (DBE) and carbon number.

Double Bond Equivalents = 122

++−NH

C 1.19

Where C, H and N corresponds to the number of carbon, hydrogen and

nitrogen atoms in the elemental formula. For example, a compound with

an assigned elemental formula of C39H57N1, belongs to the N1 class and

has a DBE value of 12. DBE is related to hydrogen deficiency. A fully

hydrogen saturated compound has a DBE of zero. Each loss of two

hydrogen atoms corresponds to a structural addition of one double bond

or ring.

Also, APPI forms radical molecular ions, M+�, and protonated

compounds [M + H]+. Calculation of the DBE for a protonated compound

13

(one additional hydrogen atom) can, thus, result in a non-integer value,

e.g., the protonated compound C39H58N1 calculates to a 11.5 DBE value

(Table 1.1). Hence, by simply calculating the DBE value from the

molecular formula of the detected ion (not the neutral species), type ion

formed in the APPI source can be determined.

Table 1.1. Example of a Crude Oil Homologous Series Categorized by Class, DBE

and Carbon Number Distribution. DBE and Molecular Formulas Correspond to the Ion as Opposed to the Neutral Compound.

Carbon IUPAC Kendrick Nominal KMD DBE Molecular Class Number Mass Mass Mass Formula 28 406.162 405.709 406 291 17.5 C28H24N1S1 N1S1 29 420.178 419.709 420 291 17.5 C29H26N1S1 N1S1 30 434.194 433.709 434 291 17.5 C30H28N1S1 N1S1 31 448.209 447.709 448 291 17.5 C31H30N1S1 N1S1 32 462.225 461.709 462 291 17.5 C32H32N1S1 N1S1 33 476.241 475.709 476 291 17.5 C33H34N1S1 N1S1 34 490.256 489.709 490 291 17.5 C34H36N1S1 N1S1 35 504.272 503.709 504 291 17.5 C35H38N1S1 N1S1 36 518.288 517.709 518 291 17.5 C36H40N1S1 N1S1 37 532.303 531.709 532 291 17.5 C37H42N1S1 N1S1 38 546.319 545.709 546 291 17.5 C38H44N1S1 N1S1 39 560.335 559.709 560 291 17.5 C39H46N1S1 N1S1

Table 1.1 is an example of a petroleum homologous series from a positive

ion APPI mass spectrum. The half integer DBE value (17.5) indicates the

type ion formed (protonated compound) in the APPI source.

14

CHAPTER 2. ATMOSPHERIC PRESSURE PHOTOIONIZATION FOURIER TRANSFORM ION CYCLOTRON RESONANCE MASS

SPECTROMETRY FOR COMPLEX MIXTURE ANALYSIS

Summary We have coupled atmospheric pressure photoionization (APPI) to a

home-built 9.4 Tesla Fourier transform ion cyclotron resonance (FT-ICR)

mass spectrometer. Analysis of naphtho[2,3-a]pyrene and crude oil

mass spectra reveals that protonated molecules, deprotonated molecules

and radical molecular ions are formed simultaneously in the ion source,

thereby complicating the spectra (>12,000 peaks per mass spectrum and

up to 63 peaks of the same nominal mass), and eliminating the "nitrogen

rule" for nominal mass determination of number of nitrogens.

Nevertheless, the ultrahigh mass resolving power and mass accuracy of

FT-ICR MS enabled definitive elemental composition assignments, even

for doublets as closely spaced as 1.1 mDa (SH313C vs. 12C4). APPI

efficiently ionizes nonpolar compounds that are unobservable by

electrospray and allows nonpolar sulfur speciation of petrochemical

mixtures.

Introduction

Advancements in atmospheric pressure ionization (API) techniques

have broadened the analytical possibilities for mass spectrometry.

Notably, electrospray ionization (ESI)36 and atmospheric chemical

ionization (APCI)37 have expanded the application of mass spectrometry

to the biological and pharmaceutical sciences.38, 39 Both ESI and APCI

mechanisms attach a charge to the analyte and ionization efficiency

correlates with analyte polarity. Electrospray ionization of a neutral

analyte typically occurs by addition or loss of a proton. The APCI charge

15

carrier is the product of a corona discharge, typically CH5+ from

methane, but can vary with different gas systems. These API techniques

have the advantages of ready coupling with Liquid Chromatography (LC),

can efficiently ionize polar species and to some extent less polar species,

and are robust. However, non-polar compounds are inaccessible by ESI

and can be problematic for APCI.

Atmospheric Pressure PhotoIonization (APPI) was initially

introduced as a soft ionization method through direct photoionization19-22

and later with dopant-assisted ionization coupled to LC,23 and can

produce ions of low-polarity and even non-polar species not efficiently

ionized by ESI and APCI. Field Desorption (FD) ionization40, 41 can also

produce ions from non-polar species, but (less conveniently) at less than

atmospheric pressure. An APPI ion source typically uses a vacuum

ultraviolet (VUV) gas discharge lamp (e.g., krypton at ~120 nm) and can

produce radical molecular ions from species with first ionization energies

(IE) below the photon energy. However, some typical LC solvents

(acetonitrile, methanol and/or water) deplete much of the photon flux

resulting in poor analyte ionization efficiency.26, 42-44

Poor ionization efficiency by direct photoionization is problematic.

Robb et al. have shown that the addition of a dopant, toluene, increases

sensitivity by promoting proton transfer reactions and charge exchange

reactions.23 Robb eluted four model compounds with and without a

dopant and noted a 100-fold increase in signal with a dopant for some

compounds.

Consequently, most APPI configurations have coupled LC to APPI

with a toluene dopant.45 The dopant is introduced directly into the

solvent flow post-column or infused into a stream of hot gas through the

auxiliary gas port of the APPI source heated nebulizer. Toluene has a

first IE of 8.3 eV14 (lower than that of the photons from the VUV lamp)

and is typically infused at a flow rate that results in a relative molar

concentration much higher than that of the analyte. The combination of

16

low first ionization energy and high molar concentration increases the

statistical probability that an analyte ion will form because the abundant

dopant radical molecular ions collide reactively with the analyte.23, 27

There are two primary ionization products for a neutral analyte in

the APPI source. With toluene dopant, if the proton affinity of the analyte

is higher than the proton affinity of the benzyl radical, a protonated

molecule can form.23, 27 If the electron affinity of the toluene radical

cation is higher than the electron affinity of the analyte (lower or equal

ionization energy than toluene), a radical molecular ion can form. The

possibility of forming two ion types from a single analyte can further

complicate an already complex spectrum. High mass resolving power

and mass accuracy are particularly essential for APPI MS.

Greig et al. first coupled APPI to Fourier Transform Ion Cyclotron

Resonance (FT-ICR) mass spectrometry, and applied it to the analysis of

corticosteroids.46 In this work, we couple APPI with a 9.4 Tesla FT-ICR

mass spectrometer10 to evaluate model compounds as well as complex

mixtures. We chose petroleum crude oil for demonstration, because it

contains both polar and non-polar constituents, and represents the most

complex natural mixture over a relative abundance dynamic range of

~104. We further demonstrate that the ultrahigh mass resolving power

and ultrahigh mass accuracy of FT-ICR MS7 are essential for analysis of

complex mixtures by APPI mass spectrometry.

Experimental Methods

Solvents and Compounds

All solvents were HPLC grade and purchased from Fisher.

Naphtho[2,3-a]pyrene was purchased from Sigma-Aldrich and dissolved

in toluene or an isomeric mixture of hexanes to produce a 3 mM stock

17

solution. Two serial dilutions resulted in a 30 µM final concentration in

toluene or hexane.

Crude Oil

Each crude oil was supplied by ExxonMobil and a sample (2.5 g)

was fractionated according to the Saturates-Aromatics-Resins-

Asphaltenes (SARA) method.47 The crude oil was dissolved in 20 mL of

toluene and rotary vacuum evaporated to approximately 5 mL volume to

remove the volatiles. The sample was then completely dried under a

stream of nitrogen gas. The dried sample was dissolved in n-hexane (25

mL) and gravity filtered through Whatman 2V grade paper to remove the

asphaltenes. The filtrate (maltenes) was rotary vacuum-evaporated to 5

mL volume, absorbed onto aluminum oxide (Al2O3, 5.2 g), and dried

under a stream of nitrogen gas with gentle stirring. The alumina was

then packed on top of neutral alumina (15.0 g) in an 11 x 300 mm open

column. The aliphatics were eluted with hexane (80 mL) and the

aromatics subsequently eluted with toluene (80 mL), and the resins with

80:20 toluene/methanol (80 mL). The aromatic sample was rotary

vacuum-evaporated to dryness and weighed (1.13 g) and re-dissolved in

toluene (11 mL) to produce a stock solution of 100 mg/mL. The stock

solution was further diluted to 1 mg/mL in toluene for analysis.

Results And Discussion

FT-ICR MS can simultaneously analyze ions spanning several

decades in mass-to-charge ratio (m/z), over a vertical dynamic range of

up to 104, with ultrahigh resolving power and mass accuracy.7 Time-of-

flight and quadrupole mass spectrometers have lower mass resolving

power and usually require a liquid chromatography (LC) preseparation

step prior to mass analysis of complex mixtures. Therefore, FT-ICR MS

18

can negate the need for a preseparation step by combining both

resolution and mass measurement in one step.

Although crude oil is the most compositionally complex organic

mixture (over a dynamic range of 104); ESI FT-ICR MS has enabled the

detailed speciation of its polar components.33, 48 However, because the

electrospray ionization mechanism involves proton transfer reactions, it

selectively ionizes acids (to produce negative ions) or bases (to produce

positive ions). Thus, a limitation of ESI is that it will most efficiently

ionize the most acidic/basic species. Atmospheric pressure

photoionization, on the other hand, can ionize both polar and non-polar

compounds. Because petroleum crude oil is composed ~90% of

hydrocarbons, APPI generates mass spectral signals for species not

accessible by ESI or APCI. For example, Figure 2.1 shows heteroatom

class relative abundances for ions in a positive-ion APPI FT-ICR mass

spectrum of a Middle East crude oil. The starred classes are non-polar

classes observed by APPI and are not detected by ESI, the most notable

of which are those that contain sulfur. Sulfur speciation is particularly

important to the petroleum refining industry due to continued regulatory

decreases in the allowable sulfur levels for petroleum products. A

detailed discussion of the species observed in ESI and APPI, their

respective class based ionization trends, and APPI ionization

mechanisms in complex petroleum matrices will be reported elsewhere.

Model Compounds

Figure 2.2 shows APPI-FT-ICR positive-ion mass spectra of a

polycyclic aromatic hydrocarbon, naphtho[2,3-a]pyrene, dissolved in

toluene (top) and a mixture of isomeric hexanes (bottom) and injected

directly into the APPI source. Both spectra were collected under the

same instrumental conditions except for a doubled ion accumulation

19

S1 S2 N1 N1

S1

HC O1

S1

S3 N1

O1

N1

S2

*

*

*

*

Middle East Crude Oil

(+) APPI FT-ICR MS

* (Non-Polar Classes)

Figure 2.1. Class distribution from an APPI positive-ion FT-ICR mass spectrum of Middle East crude oil.

20

period for Figure 2.2 (bottom) to enhance the signal-to-noise ratio. Even

so, the signal to noise ratio in substantially lower for the hexanes

sample. The higher signal-to-noise ratio in Figure 2.2 (top) is attributed

to charge exchange between the toluene dopant and the analyte. In this

example, ionization efficiency is enhanced 20-fold by addition of the

dopant.

The mass scale-expanded insets in Figure 2.2 reveal another

difference between the spectra. At nominal mass 303 Da, the protonated

molecule ([C24H14 + H]+) relative abundance in hexanes (Figure 2.2,

bottom) is significantly lower than in toluene (Figure 2.2, top). In Figure

2.2 (top), the signal from the 12C24 protonated molecule at nominal mass

303 is comparable in magnitude to that for the 13C112C23 radical cation.

Lower resolving power mass analyzers would not resolve that doublet

and the resulting broadened and asymmetrical peak would yield poor

mass accuracy leading to ambiguity in peak assignment. Also in Figure

2.2 (top), three species are detected at nominal mass 304 Da. The use of

a dopant (toluene) clearly increases signal-to-noise ratio, but at the cost

of increased spectral complexity due to formation of two ion types

(radical molecular ions and protonated molecules), thereby increasing

the need for ultrahigh resolving power for reliable assignment of

elemental compositions.

The Nitrogen Rule

At nominal mass accuracy, the "nitrogen rule"49 states that an

odd-electron ion (e.g., M+●) has an even (odd) nominal mass if it contains

an even (odd) number of nitrogen atoms." Conversely, an even-electron

ion (e.g., (M+H)+ or (M-H)-) has an odd (even) nominal mass if it contains

an even (odd) number of nitrogen atoms. Thus, it is possible to

21

[C22H1413C2]

+ �

[C23H1413C + H]+

[C24H14 + 2H]+

[C23H1413C]+ �

[C24H14+ H]+

[C24H14]+ �

m/z

305304303302301

m/z

303.13303.12303.11303.10

m/z

304.13304.12304.11

Naphtho[2,3-a]pyrene

m/z305304303302301

[C22H1413C2]

+ �

[C23H1413C + H]+

[C23H1413C]+ � [C24H14+ H]+

[C24H14]+ �

Naphtho[2,3-a]pyrenem/z

303.12303.10303.08 303.14

m/z304.12304.10304.08 304.13

(+) APPI FT-ICR MS

in Toluene

in Hexanes

Figure 2.2. APPI positive-ion FT-ICR mass spectra of 30 µM naphtho[2,3-a]pyrene in toluene (top) and hexanes (bottom). Top: The insets show the two kinds of ions formed in the APPI source region; protonated molecules and radical molecular cations. Nine acquisitions were summed with an external ion accumulation of 5 seconds each, resulting in a SNR of 2300. Bottom: The insets show the reduction in formation of the protonated molecule in the absence of a dopant. Nine acquisitions were summed with an external ion accumulation of 10 seconds each.

22

determine whether the number of nitrogens is even or odd based on

appearance of a mass spectral signal at even or odd nominal mass,

provided that all ions are either even-electron (as in electrospray

ionization or matrix-assisted laser desorption ionization) or odd-electron

(as in electron ionization). However, because APPI can produce both

even- and odd-electron ions in the same spectrum, the "nitrogen rule"

can no longer be used to determine the number of nitrogens based on

nominal mass alone. Again, ultrahigh-resolution and mass accuracy are

needed to derive the correct elemental composition.

Complex Mixture Analysis

Formation of both protonated molecules and radical ions obviously

increases the number of peaks per nominal mass. In Figure 2.2 (top), at

nominal mass 303, the difference between [C23H1413C]+� and [C24H14+ H]+

is 4.5 mDa (13C vs. CH), requiring mass resolving power of at least

130,000 (and proportionately higher at higher mass and/or for unequal

relative abundance) for correct elemental composition assignment. In a

complex mixture, FT-ICR MS routinely achieves ultrahigh mass resolving

power (e.g., 400,000 resolving power at 400 Da), m/∆m50%, in which

∆m50% is the mass spectral peak full width at half-maximum peak

height.7 For example, Figure 2.3 shows a mass scale-expanded segment

of a positive-ion APPI FT-ICR mass spectrum of a South American crude

oil. A single crude oil mass spectrum can contain thousands of peaks.50,

51 The 3.4 mDa separation seen in Figure 2.3 is the mass difference

between C3 and SH4, a common mass doublet in crude oil. That mass

difference is also seen by electrospray ionization because both species

are amenable to proton transfer reactions and can produce protonated

molecules. Furthermore, the formation of both radical

23

m/z

481.45481.40481.35481.30

[C35H44O1 + H]+

[C34H45N113C1 + H]+ [C35H47N1]

+ �

4.5 mDa

3.4 mDa

South American Crude Oil

3.4 mDa C3 versus SH4

4.5 mDa CH versus 13C

[C32H48O1S1 + H]+

*

*

*

*

** * *

*

*

APPI FT-ICR MS

Figure 2.3. APPI FT-ICR mass scale-expanded segment for a South American crude oil. The mass doublets document the requirement for ultrahigh mass resolving power with an APPI source for complex mixture analysis. The 3.4 mDa mass doublet corresponds to species differing by C3 vs. SH4 and the 4.5 mDa mass doublet to 12CH vs. 13C. Two hundred acquisitions were summed with an ion accumulation of 3 seconds each. Starred peaks were assigned to elemental compositions not shown in the Figure.

24

cations and protonated molecules in the APPI source can produce an

additional 4.5 mDa split (13C vs. CH).

Figure 2.4 shows a mass scale-expanded segment of a positive-ion

APPI FT-ICR mass spectrum of a Middle East crude oil known to be high

in sulfur content.52 The combination of high sulfur content and two

ionization pathways produces yet another mass doublet, separated by

only 1.1 mDa, corresponding to the mass difference between C4 and

SH313C from the protonated molecule [C24H29N1S1

13C1 + H]+ and the

radical molecular ion [C28H27N1]+�. That doublet is not seen in ESI

spectra because radical cations are not observed by ESI for crude oil

samples.

Negative Ions

Negative ions are formed along with positive ions in the APPI

source and may be detected with appropriate instrument polarity

changes. Figure 2.5 (bottom) is a negative-ion APPI FT-ICR broadband

mass spectrum of a South American crude oil and further demonstrates

the remarkable and necessary analytical power of FT-ICR MS. Across

the spectrum, unique elemental compositions could be assigned to

12,449 spectral peaks: the most compositionally complex resolved mass

spectrum to date. Within the 400 Dalton mass window, an average mass

resolving power of ~400,000 and an rms mass accuracy of 260 parts per

billion was achieved. An example of the complexity is shown in the mass

scale expansion (Figure 2.5 top). There are 63 spectral peaks with

magnitude exceeding 8 σ of rms baseline noise, and unique elemental

compositions could be assigned to 62 of them (see Table 2.1) based solely

on mass accuracy and Kendrick analysis.

25

m/z377.24377.23377.22377.21377.20377.19

[C28H27N ]+ �[C24H29 N1S113C1 + H]+

1.1 mDaMiddle East Crude Oil

1.1 mDa SH313C1 versus C4

*

**

*

*

*

*

*

APPI FT-ICR MS

Figure 2.4. APPI FT-ICR mass scale-expanded segment of a high-sulfur Middle East crude oil, showing a very close 1.1 mDa mass doublet, 12C4 vs. SH313C. Two hundred acquisitions were summed with an external ion accumulation of 5 seconds each. Starred peaks were assigned to elemental compositions not shown in the Figure.

26

Table 2.1 Elemental Compositions Assigned to Peaks in the Negative-ion APPI FT-ICR Mass Spectral Segment Shown in Figure 2.5. All elemental compositions are for the deprotonated molecule, (M-H)-. Note that measured and calculated masses are uniformly identical to six places, and differ only at the sub-ppm level (shown in red).

Peak Elemental Measured Calculated ppm No. Composition Mass Mass error 1 C24H15O4S2 431.04159 431.04172 -0.31 2 C20H15O9S1 431.04420 431.04423 -0.06 3 C24H15O6S1 431.05944 431.05948 -0.10 4 C21H19O6S2 431.06272 431.06285 -0.31 5 C28H15O3S1 431.07477 431.07474 0.07 6 C24H15O8 431.07723 431.07724 -0.03 7 C21H19O8S1 431.08055 431.08061 -0.14 8 C28H15O5 431.09242 431.09250 -0.18 9 C25H19O5S1 431.09580 431.09587 -0.16 10 C22H23O5S2 431.09921 431.09924 -0.07 11 C29H19O2S1 431.11112 431.11112 -0.01 12 C25H19O7 431.11361 431.11363 -0.04 13 C22H23O7S1 431.11698 431.11700 -0.04 14 C19H27O7S2 431.12043 431.12037 0.14 15 C29H19O4 431.12886 431.12888 -0.05 16 C26H23O4S1 431.13225 431.13225 -0.01 17 C23H27O4S2 431.13559 431.13562 -0.08 18 C26H23O6 431.15000 431.15001 -0.03 19 C25H24N1O3S1

13C1 431.15135 431.15159 -0.56 20 C23H27O6S1 431.15336 431.15338 -0.05 21 C20H31O6S2 431.15675 431.15675 -0.01 22 C30H23O3 431.16528 431.16527 0.03 23 C27H27O3S1 431.16863 431.16864 -0.02 24 C24H31O3S2 431.17203 431.17201 0.05 25 C20H31O8S1 431.17449 431.17451 -0.05 26 C29H24N1O2

13C1 431.18446 431.18461 -0.34 27 C27H27O5 431.18638 431.18640 -0.04 28 C26H28N1O2S1

13C1 431.18769 431.18798 -0.67 29 C24H31O5S1 431.18976 431.18977 -0.02 30 C21H35O5S2 431.19311 431.19314 -0.07 31 C31H27O2 431.20161 431.20165 -0.10 32 C28H31O2S1 431.20499 431.20502 -0.08 33 C24H31O7 431.20746 431.20753 -0.16 34 C23H32N1O4S1

13C1 431.20918 431.20911 0.17 35 C21H35O7S1 431.21084 431.21090 -0.13 36 C30H28N1O1

13C1 431.22103 431.22099 0.09 37 C28H31O4 431.22276 431.22278 -0.05

27

Table 2.1 - continued Peak Elemental Measured Calculated ppm No. Composition Mass Mass error 38 C27H32N1O1S1

13C1 431.22411 431.22436 -0.59 39 C25H35O4S1 431.22612 431.22615 -0.08 40 C22H39O4S2 431.22951 431.22952 -0.03 41 C29H35O1S1 431.24129 431.24141 -0.28 42 C27H32N1O3

13C1 431.24212 431.24212 -0.01 43 C25H35O6 431.24386 431.24391 -0.12 44 C22H39O6S1 431.24726 431.24728 -0.05 45 C31H31N2 431.24910 431.24927 -0.40 46 C31H32N1

13C1 431.25737 431.25738 -0.02 47 C29H35O3 431.25911 431.25917 -0.14 48 C28H36N1S1

13C1 431.26053 431.26075 -0.51 49 C26H39O3S1 431.26246 431.26254 -0.18 50 C28H36N1O2

13C1 431.27843 431.27851 -0.18 51 C26H39O5 431.28020 431.28030 -0.23 52 C23H43O5S1 431.28361 431.28367 -0.14 53 C30H39O2 431.29546 431.29555 -0.22 54 C27H43O2S1 431.29879 431.29892 -0.31 55 C29H40N1O1

13C1 431.31485 431.31489 -0.10 56 C27H43O4 431.31659 431.31668 -0.22 57 C24H47O4S1 431.31997 431.32005 -0.20 58 C31H43O1 431.33184 431.33194 -0.23 59 C28H47O1S1 431.33520 431.33531 -0.26 60 C30H44N1

13C1 431.35122 431.35128 -0.14 61 C28H47O3 431.35301 431.35307 -0.14 62 C29H51O2 431.38948 431.38945 0.06

Mass accuracy

Figures 2.6 and 2.7 graphically demonstrate the unrivaled mass

accuracy of FT-ICR MS, by showing the relation between peak magnitude

and mass error (i.e., difference between experimentally measured mass

and the exact mass corresponding to the elemental composition assigned

to that mass spectral peak). The precision in measurement of peak

position should be linearly proportional to the mass spectral peak signal-

to-noise ratio (SNR) and the square root of the number of data points per

28

m/z

431.4431.3431.2431.1431.0

8 σ

m/z700640580520460400340280

*

63 Spectral Peaks above 8 σ62 Spectral Peaks Assigned

* Not assigned

APPI FT-ICR MS

Figure 2.5. Negative ion APPI FT-ICR broadband mass spectrum of a South American crude oil. Bottom: Across a 400 Dalton mass window, 12,449 unique elemental compositions (a new record for a single mass spectrum) were assigned (> 99% deprotonated molecules), based on an average mass resolving power of ~400,000 and an rms mass accuracy of 260 parts per billon. Top: At a S/N ratio > 8 σ of baseline noise, there are 63 spectral peaks of nominal mass 377 Da of which unique elemental compositions could be assigned to 62 (see Table 2.1).

29

Figure 2.6. APPI FT-ICR mass spectral peak magnitude vs. mass error (measured

mass minus the exact mass for the assigned chemical formula) for the elemental compositions assigned to 12,449 spectral peaks from Figure 2.5. Ninety percent of the peaks exhibit less than 500 ppb mass error. As predicted,53 mass accuracy increases with increasing mass spectral S/N ratio.

0

250

500

750

1000

1250

1500

-1 0 1

Nu

mb

er

of

Assig

ned

Masses p

er

Bin

50 ppb Mass Bins

400 ppb

(-) APPI

FT-ICR MS

Mass Error, ppm

12,449

Assigned

Masses

S. American

Crude Oil

Figure 2.7. Mass error distribution for the 12,449 spectral peaks from Figure 2.5. Each bar represents the number of assigned masses within a 50 ppb "bin" mass error range. At half-maximum height, the errors span a range of ±200 ppb.

30

peak width.53 Fig. 2.6 shows that the mass error does increase as peak

signal-to-noise ratio decreases as expected; nevertheless, 90% of the

peaks exhibit less than 500 parts-per-billion mass error. Figure 2.7

shows a more conventional mass error distribution, based on counting

the number of peaks in each 50 ppb mass error "bin". The errors are

Gaussian-distributed, with an rms deviation of ±200 ppb. The data in

Figures 2.6 and 2.7 constitute the most definitive measures of

broadband mass measurement accuracy, especially at low signal-to-

noise ratio.

Conclusions

Atmospheric pressure photoionization is useful for analysis of low-

polarity and non-polar compounds. A dopant is typically necessary to

increase sensitivity by promotion of proton transfer and charge exchange

reactions. Toluene works well because it can act as a proton donor (or,

the toluene radical cation, as an electron acceptor) and participate in

reactions which produce both cations and anions. Protonated molecules

(and deprotonated molecules) and radical molecular ions are formed

simultaneously. As a result, APPI can add complexity to mass spectra.

FT-ICR MS overcomes that complication. APPI FT-ICR MS is uniquely

suited to analysis of complex petrochemical mixtures that naturally

contain a large proportion of low-polarity or non-polar aromatic

hydrocarbons, and for analysis of fullerene mixtures.54

31

CHAPTER 3. COMPARISON OF ATMOSPHERIC PRESSURE

PHOTOIONIZATION AND ELECTROSPRAY IONIZATION OF CRUDE OIL NITROGEN CONTAINING AROMATICS BY FOURIER TRANSFORM

ION CYCLOTRON RESONANCE MASS SPECTROMETRY

Summary

We determine the elemental compositions of aromatic nitrogen

model compounds as well as a petroleum sample by Atmospheric

Pressure Photoionization (APPI) and Electrospray Ionization (ESI) with a

9.4 Tesla Fourier transform ion cyclotron resonance (FT-ICR) mass

spectrometer. From the double bond equivalents calculated for the

nitrogen-containing ions from a petroleum sample, we can infer the

aromatic core structure (pyridinic versus pyrrolic nitrogen heterocycle)

based on the presence of M+� (odd-electron) versus [M + H]+ (even-

electron) ions. Specifically, nitrogen speciation can be determined from

either a single positive-ion APPI spectrum or two ESI (positive- and

negative-ion) spectra. APPI operates at comparatively higher temperature

than ESI and also produces radical cations that may fragment before

detection. However, APPI fragmentation can be eliminated by judicious

choice of instrumental parameters.

Introduction

Heavy petroleum characterization by mass analysis requires the

ultrahigh mass resolving power of Fourier Transform Ion Cyclotron

Resonance Mass Spectrometry (FT-ICR MS)7 to distinguish thousands of

ionic species.33, 48 Electrospray ionization (ESI) enables the analysis of

the petroleum polar constituents.32, 33 Electrospray ionization of

petroleum55 typically involves proton transfer reactions that selectively

ionize acids (to produce negative [M-H]- ions) or bases (to produce

positive [M+H]+ ions).56 The ionization efficiency correlates with acidity or

32

basicity. For example, carboxylic acids are efficiently ionized by negative-

ion ESI whereas basic species (e.g., pyridinic N1 species) are efficiently

ionized by positive-ion ESI. Acidic or basic species represent only a

small fraction of the aromatics in a petroleum sample.52

For the non-polar aromatic fraction of petroleum, Atmospheric

Pressure Photoionization21, 23 (APPI) can produce ions from species that

are not efficiently ionized by ESI. The youngest of the soft ionization

methods, dopant-assisted APPI was initially developed to interface liquid

chromatography to mass spectrometry to analyze simple mixtures. The

ionization technique is ideal for non-polar aromatic compounds because

the photon energy (typically 10 eV) is great enough to ionize species with

aromatic ring structures. However, direct photoionization is usually not

efficient45 and the addition of a dopant enhances ionization efficiency

through proton transfer reactions and charge exchange reactions.

Toluene is both a good dopant and an excellent solvent for crude oil.

Although APPI is considered to be a soft ionization technique (i.e.,

produces minimal fragmentation of most analytes), it is considered less

soft than ESI because the APPI heated nebulizer and the source region

can reach >300°C, whereas ESI is conducted at room temperature.

Furthermore, toluene dopant-assisted APPI produces radical cations26

that can participate in further gas phase reactions.

Here, we compare ESI and APPI for analysis of petroleum crude

oils. The nitrogen atom in petroleum aromatic N1 class species can

reside in a five-membered ring (pyrrolic) or six-membered ring (pyridinic),

and be readily protonated (pyrrolic) or deprotonated (pyridinic) by

negative-ion or positive-ion ESI, respectively.50 However, positive-ion

APPI efficiently generates both pyrrolic and pyridinic nitrogen signals in a

single mass spectrum.

APPI can extend the characterization of the petroleome33, 48 to

include non-polar aromatic species and enhance the extent of molecular

speciation for better understanding of petroleum processing and refining.

33

The nitrogen class species are efficiently ionized by both ESI and APPI,

and therefore offer a good basis for comparison. In this work, we couple

APPI and ESI to a 9.4 Tesla FT-ICR mass spectrometer10 for detailed

compositional comparisons of the ions produced from the same South

American crude oil.


South American Crude Oil

A South American Crude oil was supplied by ExxonMobil Research

and Engineering Company (Annandale, NJ) and a sample (2.8 g) was

fractionated according to the Saturates-Aromatics-Resins-Asphaltenes

(SARA) method.57 The SARA method produced an aromatic fraction

solution of 100 mg/mL in toluene. Two serial dilutions yielded a 2

mg/mL solution that was further diluted in toluene to 1 mg/mL for APPI

analysis and 1 mg/mL in toluene:methanol (1:1 v/v) for ESI analysis.

Nitrogen Class Compounds

Five aromatic nitrogen compounds (acridine, carbazole, 7,9-

dimethylbenz[c]acridine, 7H-dibenzo[c,g]carbazole and ellipticine) were

purchased from Sigma-Aldrich. Equimolar solutions (2 mM) of the five

nitrogen compounds were prepared in toluene. For ESI, the 2 mM

solutions were diluted by a factor of 5 in toluene to 400 µM, and

subsequently equal aliquots (100 µL) of the five compound solutions

were combined and diluted with methanol (1:1 v/v) to produce a final

concentration of 40 µM for each compound. For APPI, equal aliquots (2

mL) of 2 mM solutions were combined to yield 400 µM (10 mL) for each

compound, followed by a 1:10 dilution to 40 µM for each analyte.

34

ESI Experimental Conditions

One end of a 50 µm i.d. fused silica tube was in-house ground to a

point and used as the microelectrospray source58] to produce

electrosprayed positive and negative ions. General conditions were:

needle voltage, 2 kV (-2 kV negative-ion electrospray); tube lens, 350 V (-

350 V negative-ion electrospray); and heated metal capillary current, 4.0

amperes. ESI negative-ion conditions were comparable to ESI positive-

ion conditions.

Results and Discussion

Nitrogen Compounds

Figure 3.1 shows the possible ionization pathways for aromatic N1

class compounds (acridine and carbazole) by APPI (positive-ion) and ESI

(negative-ion and positive-ion). The two pathways involving proton

transfer yield even-electron [M+H]+ or [M-H]- ions with half-integer DBE

values. Positive-ion APPI can also form odd-electron radical cations with

integer DBE values.

Five nitrogen compounds (Figure 3.2) were selected as petroleum

model compounds: two pyrrolic (five-membered ring), two pyridinic (six-

membered ring), and one (ellipticine) with one of each ring type. Figure

3.3 shows the positive-ion (bottom) and negative-ion (top) ESI spectra of

an equimolar solution of the nitrogen compounds. The pyrrolic nitrogen

species deprotonate to form [M-H]- ions, whereas the pyridinic species

protonate to form [M+H]+ ions.

35

.

N N

N

H

N

H

Positive ESI

+

-

+

Negative ESI

Positive APPI

10 DBE

9 DBE

9.5 DBE

9 DBE

9.5 DBE

Carbazole

Acridine

+ H

- H

N

H

Positive APPI

Figure 3.1. ESI and APPI ionization pathways for acridine and carbazole. For ESI, negative-ion and positive-ion spectra would be necessary to detect both species. However, both compounds yield APPI positive ions. Double bond equivalents (DBE) are calculated from Eq. 1.19 for each ion.

N

CH3

CH3

N

N

H

N

H

N

N

CH3

CH3 H

7,9-dimethylbenz[c]acridineC19H15N MW- 257.120

13 DBE

AcridineC13H9N MW- 179.073

10 DBE

CarbazoleC12H9N MW- 167.073

9 DBE

ElipticineC17H14N2 MW- 246.115

12 DBE

7H-Dibenzo[c,g]carbazoleC20H13N MW- 267.104

15 DBE

Figure 3.2. Nitrogen class compounds. Carbazole and 7H-dibenzo[c,g]carbazole are pyrrolic (acidic), whereas acridine and 7,9-dimethylbenz[c]acridine are pyridinic (basic) species. Ellipticine, with two nitrogen heteroatoms, has both pyrrolic and pyridinic moieties.

36

Figure 3.4 shows positive-ion (bottom) and negative-ion (top) APPI

spectra of an equimolar solution of the nitrogen compounds. Both

positive and negative ions are formed simultaneously in the source,

enabling detection of either positive or negative ions by appropriate

instrument polarity changes and no source interruption. The APPI

negative-ion spectrum shows the deprotonated pyrrolic species.

However, in the APPI positive-ion spectrum, all five nitrogen compounds

are detected simultaneously. The pyrrolic species form radical molecular

ions and the pyridinic species form protonated compounds.

The pyrrolic compounds (carbazole and 7H-dibenzo[c,g]carbazole)

exhibit different ionization efficiency (and ion type) in negative-ion and

positive-ion APPI mass spectra. Carbazole (7.6 eV ionization energy)59

forms radical molecular cations less efficiently than the more extensively

conjugated 7H-dibenzo[c,g]carbazole (7.1 eV ionization energy).59 In

contrast, negative-ion APPI generates much more similar [M-H]- ion

abundances for both carbazoles (Figure 3.4 top).

Nitrogen Class Speciation

Figure 3.5 is the positive-ion APPI broadband mass spectrum of a

South American crude oil, including various closely-spaced mass

doublets. First, a 3.4 mDa separation (zoom inset in Figure 3.5) results

from two compounds that differ in elemental composition by C3 vs. SH4,

a common mass doublet from crude oil. That mass difference is also

seen by electrospray ionization because both species can produce

protonated compounds.

37

m/z280270260250240230220210200190180170160

Positive ESI

N

+ H+

N

N

CH3

CH3 H

+ H+

N

CH3

CH3

+ H

+

m/z

280270260250240230220210200190180170160

Negative ESI

N

H

N

H

N

N

CH3

CH3 H

- H-

- H

-

- H

-A

B

Figure 3.3. Negative-ion and positive-ion ESI FT-ICR mass spectra of representative nitrogen-class compounds. For both spectra, an equimolar solution was electrosprayed. The pyrrolic species were ionized by negative-ion ESI and the pyridinic species by positive-ion ESI. Ellipticine was detected in both negative-ion and positive-ion spectra.

38

m/z

280270260250240230220210200190180170160

Negative APPI

N

H

N

H

N

N

CH3

CH3 H

- H-

- H

-

- H

-

m/z

280270260250240230220210200190180170160

Positive APPI

N

+ H+

N

CH3

CH3

+ H

+

N

H

N

H

N

N

CH3

CH3 H

+ H

+

+�

+�

A

B

Figure 3.4. Negative-ion and positive-ion APPI spectra of representative nitrogen-class compounds. For both spectra, an equimolar solution was infused into the APPI source. The pyrrolic species were detected in the negative-ion APPI spectrum, and all five compounds were detected in the positive-ion APPI spectrum.

39

Second, APPI can produce an additional 4.5 mDa split (13C vs.

12CH) doublet not seen by ESI, due to formation of both a radical

molecular ion (M+�) and protonated molecule ([M + H]+) from the same

neutral precursor. Naptho[2,3-a]pyrene was added as a standard to test

for fragmentation (see below), i.e, no spectral peaks corresponding to loss

of one or two hydrogen atoms from naptho[2,3-a]pyrene were observed.

The spectral peaks from the broadband spectrum were assigned

unique molecular formulas based on accurate mass measurement for

homologous series.34 Similar broadband spectra were acquired (data not

shown) for positive- and negative-ion ESI. The N1 class ions were sorted

by DBE and carbon number. Figure 3.6 is the DBE distribution for the

APPI positive-ion nitrogen class species and the ESI negative- and

positive-ion nitrogen classes.

The DBE values in Figure 3.6 were calculated from Eq. 1.19 for the

ion molecular formulas. Accordingly, half-integer DBE values result for

even-electron (protonated or deprotonated compound) ions, [M+H]+ or [M-

H]-, whereas integer DBE values result for odd-electron ions (e.g., radical

cations, M+�). Hence, the DBE value calculated from Eq. 1.19 for any

N1-class aromatic compound readily distinguishes even-electron

(pyridinic, half-integer DBE) from odd-electron (pyrrolic, integer DBE)

ions produced by APPI.

From the DBE distribution (Figure 3.6 top), it is clear that APPI

produces both protonated compounds (half integer DBE) and radical

molecular ions (integer DBE). Interestingly, the radical molecular ions

begin at DBE 9, the same DBE threshold observed for negative even-

electron [M-H]- ions. In fact, if the negative-ion ESI DBE distributions is

shifted one-half DBE lower (to compensate for the one-proton difference

40

4.5 mDa 3.4 mDa

Naphtho[2,3-a]pyrene

Internal Standard

a

b

c

[C31H29N1 13C1]

+�

[C32H29N1 + H]+

[C29H33N1 S1 + H]+

a

b

c

m/z600560520480440400360320280

m/z428.26428.24428.22

Figure 3.5. Positive-ion APPI FT-ICR broadband mass spectrum of a South

American crude oil. Both radical molecular ions and protonated compounds are formed in the APPI source. The mass scale-expanded inset shows two common spectral peak doublets for APPI. Naphtho[2,3-a]pyrene was added to the petroleum sample to test for possible fragmentation. No fragment ions were observed.

41

in mass between [M-H]- and M+�), then the negative- and positive-ion ESI

DBE distributions are essentially the same as the combined [M+H]+ and

M+� distribution from APPI.

Table 3.1 lists the elemental compositions assigned to the APPI

positive N1-class ions (DBE 9) and ESI negative N1-class ions (DBE 9.5).

Note that the neutral molecular formulas are the same for both kinds of

ions. The same behavior is seen throughout the nitrogen class DBE

distributions: i.e, the neutral elemental compositions inferred from the

deprotonated (negative-ion) ESI ions are also seen for the positive-ion

APPI ions at one-half integer lower DBE. Furthermore, the relative DBE

abundances (APPI DBE 9 vs. ESI DBE 9.5, Figure 3.6) agrees with the

nitrogen class compound spectra (Figures 3.3 and 3.4): i.e., a carbazole

type core structure compound will form a radical molecular ion (APPI

positive-ion, 9 DBE) less efficiently (Figure 3.4 bottom) than in negative-

ion ESI (9.5 DBE) (Figure 3.3 top). Moreover, as the DBE increases for

the pyrrolic species (which form radical molecular ions, integer DBE) in

the positive-ion APPI DBE distribution, the relative DBE abundance also

increases in agreement with the nitrogen compound spectra.

Ion Fragmentation

Ion dissociation is more prevalent in APPI than ESI due to hot

gases and radical ion formation. Fragmentation can be minimized (or

eliminated) by proper choice of source pressure and tube lens voltage.

The APPI source interfaces with the first stage of the mass spectrometer

through a heated metal capillary (HMC) mounted to a homebuilt

42

Negative ESI

APPI

Positive

ESI

3.5

4

4.5

5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

10

10.5

11

11.5

12

12.5

13

13.5

14

14.5

15

15.5

16

16.5

17

17.5

18

18.5

19

19.5

20

20.5

21

21.5

22

22.5

23

23.5

24

24.5

DBE

Figure 3.6. ESI (positive-ion and negative-ion) and APPI (positive-ion) DBE distributions for the N1 class from the petroleum sample. The ion DBE is calculated from Equation 1.19. The total relative ion abundance for each DBE is plotted on the y-axis. For ESI, protonation or deprotonation yield ions of half-integer DBE values. For APPI, radical molecular ions yield integer DBE values. Note that positive-ion APPI can distinguish pyridinic (M+H)+ from pyrrolic (M+�) nitrogen ions based on their respective integer and half-integer DBE values.

43

Table 3.1. List of DBE 9 positive-ion N1-class APPI species (M+�) and the DBE 9.5 negative–ion N1-class ESI species (M-H)-. Each molecular formula (and the DBE value computed from it (Eq. 1.19)) is for the stated ion, not its neutral precursor.

Experimental Ion DBE Calculated ppm m/z Formula Mass error APPI [M]+� 461.4016 C33H51N1 9 461.4016 0.00 475.4172 C34H53N1 9 475.4173 -0.11 489.4329 C35H55N1 9 489.4329 0.00 503.4484 C36H57N1 9 503.4486 -0.30 517.4643 C37H59N1 9 517.4642 0.19 ESI negative [M - H]- 460.3948 C33H50N1 9.5 460.3949 -0.10 474.4105 C34H52N1 9.5 474.4105 -0.01 488.4261 C35H54N1 9.5 488.4262 -0.15 502.4418 C36H56N1 9.5 502.4418 -0.03 516.4574 C37H58N1 9.5 516.4575 0.01

adapter (Figure 3.7). At the exit of the HMC, an open-ended cylindrical

tube (tube lens) focuses the ion flux in front of a conical shaped

skimmer. The skimmer is a pressure conductance limit (1 mm orifice)

between the first stage of the mass spectrometer and the second stage

that houses the first octopole ion guide/trap. A convectron gauge senses

the pressure in the first stage (~2.1 Torr for ESI conditions) and a direct

current potential (350 V for ESI) is applied to the tube lens. Depending

on pressure in the tube lens and the skimmer region, ion fragmentation

can ensue.60, 61

The APPI source produces hot gas at the inlet of the HMC,

resulting in elevated gas temperature in the first stage (skimmer region)

of the mass spectrometer and reduced pressure. Furthermore, tube lens

voltage >200 V in combination with increased temperature for APPI can

cause significant fragmentation.

44

DC Voltage

Atmospheric

pressure ~ 2 Torr 10-3 Torr

SkimmerTube Lens

Heated Metal Capillary

Not drawn to scale

Figure 3.7. Schematic representation (not to scale) of the Heated Metal Capillary (HMC), tube lens, and skimmer housed in the first differentially pumped stage of the mass spectrometer. Ions are transferred through the HMC and are focused by the tube lens before reaching the skimmer conductance limit. The gas dynamics in the tube lens/skimmer region can cause fragmentation but fragmentation can be negated by appropriate pressure and voltage adjustments (see text).

45

The mass spectra of naphtho[2,3,a]pyrene (C24H14) in Figure 3.8 at

different skimmer region pressure and tube lens voltage illustrate

fragmentation. In panels A and B, the tube lens voltage is held constant

and the skimmer region pressure is lowered from 2.1 Torr (A) to 1.8 Torr

(B) by partial valve closure at the vacuum pump. At 1.8 Torr, a

fragmentation threshold is reached. The mass scale-expanded inset (B)

shows formation of [C24H12]+�, a fragment formed by the loss of two

hydrogen atoms. In panels C and D of Fig. 3.8, the skimmer region

pressure is maintained at 2.1 Torr and the tube lens voltage is varied. At

increased tube lens voltage (D), the loss of one hydrogen atom from the

monoisotopic precursor, [C24H13]+� at mass 301 Da, is also observed.

Furthermore, under conditions at which fragmentation occurs (B,

C, and D in Fig. 3.8), the magnitude (zoom inset data not shown) of the

[C24H14+H]+ spectral peak relative to that of [C24H14]+� decreases as

fragmentation increases. All other spectra in this work were acquired

under Figure 3.8, panel A conditions.

Conclusions

Positive-ion APPI spectra yield the same information as combined

positive- and negative-ion ESI spectra for N1 class aromatics. Also, ESI

and APPI mass analysis of a petroleum sample can yield aromatic core

structural information. Although pyridinic and pyrrolic species

ionization efficiency depends on ionization method, APPI can generate

positive ions for both pyridinic and pyrrolic compounds, albeit at

different efficiency. The DBE values for the APPI positive-ion species

differ by 0.5 for odd- and even-electron ions, and can distinguish pyrrolic

from pyridinic nitrogen class species in a petroleum sample.

46

Figure 3.8. Positive-ion APPI FT-ICR mass spectra of naphtho[2,3-a]pyrene (C24H14, neutral monoisotopic mass, 302.110 Da) for various choices of tube lens voltage and skimmer region pressure. Fragmentation is evident at higher tube lens potential and/or lower pressure. At a tube lens potential of 200 V DC and a skimmer region pressure of 2.1 Torr, no fragmentation was observed.

47

APPI increases the thermal energy of analyte and atmosphere

gases in the source region. The increase in thermal energy changes the

gas dynamics of the mass spectrometer and can induce fragmentation.

Nevertheless, the fragmentation can be monitored and negated by proper

choice of instrumental parameters. In this work, the good agreement in

speciation of the aromatic nitrogen class species between a proven soft

ionization technique (ESI) and APPI suggest that APPI can be conducted

so as to virtually eliminate fragmentation.

48

CHAPTER 4. ATMOSPHERIC PRESSURE PHOTOIONIZATION PROTON TRANSFER FOR COMPLEX ORGANIC MIXTURES

INVESTIGATED BY FOURIER TRANSFORM ION CYCLOTRON RESONANCE MASS SPECTROMETRY

Summary

To further clarify the extent and mechanism for proton transfer in

Atmospheric Pressure PhotoIonization (APPI), we employ ultrahigh-

resolution FT-ICR mass analysis to identify M+�, [M + H]+, [M - H]- and

[M + D]+ species in toluene or perdeuterotoluene for an equimolar

mixture of five pyrollic and pyridinic nitrogen heterocylic model

compounds, as well as for a complex organic mixture (Canadian

Athabasca bitumen middle distillate). In the petroleum sample, the

protons in the [M + H]+ species originate primarily from other

components of the mixture itself, rather than from the toluene dopant.

In contrast to electrospray ionization, in which basic (e.g., pyridinic)

species protonate to form [M + H]+ positive ions and acidic (e.g., pyrrolic)

species deprotonate to form [M - H]- negative ions, APPI generates ions

from both basic and acidic species in a single positive-ion mass

spectrum. Ultrahigh-resolution mass analysis (in this work, m/∆m50% =

500,000, in which ∆m50% is the mass spectral peak full width at half-

maximum peak height) is needed to distinguish various close mass

doublets: 13C vs. 12CH (4.5 mDa), 13CH vs. 12CD (2.9 mDa), and H2 vs. D

(1.5 mDa).

Introduction

Atmospheric Pressure Photoionization (APPI) forms positive ions

through several mechanisms that include proton transfer reactions.23, 45

As for Electrospray Ionization (ESI), a protic compound must be present

in solution or the gas phase to facilitate efficient proton transfer. ESI

49

solutions typically include an acid (positive ion) or base (negative ion) at

~1 % by volume. Likewise, APPI can have an additional protic solvent

added to solution. For example, acetonitrile or methanol has been used

successfully to increase protonation of neutral analytes. 27, 62

Furthermore, toluene is often added as a dopant to increase ion yield by

proton transfer and/or charge exchange reactions.26, 63 Specifically for

protonation, a compound with a higher proton affinity than the benzyl

radical will form the desired [M + H]+ ion.23, 27 Conversely, charge

exchange reactions can produce M+� if the ionization potential of the

toluene cation is higher than that of the analyte.

Anions can also form in the APPI source. Acidic species can

deprotonate to form (M – H)- and positive electron affinity compounds can

capture thermal electrons and form M-�. Kostiainen et al. studied

negative ion formation mechanisms by investigating ionization efficiency

and ion type (even- or odd-electron ion) for analytes of different polarity

in various solvents.27, 64 Traldi et al. reported negative ion formation by

resonant electron capture from thermal electrons originating from metal

surfaces and dopant.65

Appropriately, these positive and negative ion formation

mechanistic studies have involved various compounds mass analyzed

sequentially. The molecular structure (i.e., polarity) of the selected

compounds and solvent system govern the efficiency of positive and

negative ion formation and the proton donor species could be

theoretically and experimentally determined.

However, complex mixtures can contain many potential proton

donors. Negative and positive ions can be formed simultaneously in the

APPI source. Furthermore, negative-ion APPI Fourier Transform Ion

Cyclotron Resonance (FT-ICR) mass spectrometry of a crude oil can

produce > 12 000 spectral peaks in which more than 99 % arise from

deprotonated compounds (i.e., proton donors).66 In this work, we couple

APPI with a 9.4 Tesla FT-ICR mass spectrometer9 for analysis of a

50

petroleum sample to investigate proton transfer reactions with

deuterated toluene, and thereby determine the extent of toluene’s

contribution to protonation (deuteration) of analytes ions in a complex

mixture. The complexity of the petroleum sample and the presence of

close mass doublets (see below) requires the high resolution and mass

accuracy afforded by FT-ICR mass spectrometry7 to resolve and assign

molecular formulas to the various deuterated vs. protonated compounds.


Solvents and Compounds

Model compounds and deuterated toluene (C7D8) were purchased

from Sigma-Aldrich (St. Louis, MO). The aromatic nitrogen compounds

were prepared in equimolar concentration (50 µM) in deuterated toluene.

Crude Oil

Three Athabasca Canadian bitumen distillates were provided by

the National Centre for Upgrading Technologies (NCUT), Devon, Alberta,

Canada. The bitumen distillation cuts were diluted in toluene (500

µg/mL) or deuterated toluene and analyzed without further preparation.

A Thermo Fisher Scientific (Lakewood, NJ) CHNS-O Flash EA elemental

analyzer provided element weight percent for the bitumen (2200 ppm

nitrogen content).


Canadian bitumen tar sands have a relatively high nitrogen

content. ESI FT-ICR mass spectrometry efficiently ionizes the acidic

51

(pyrrolic) and basic (pyridinic) nitrogen classes in petroleum through

proton transfer reactions.33, 51, 56 Prior APPI analysis of a petroleum

sample and nitrogen model compounds showed similar ionization trends

(compared to ESI) for aromatic nitrogen compounds with additional

radical molecular cation formation (primarily for other heteroatom class

compounds). Aromatic nitrogen species preferentially form (M + H)+ or

(M – H)- in the APPI source and therefore, provide a good test bed for

investigation of proton transfer reactions in complex mixtures.

Nitrogen Class Compounds

Five aromatic nitrogen compounds (Figure 4.1) were chosen to

model the proton transfer reaction. The structure of the

N

CH3

CH3

N

N

H

N

H

N

N

CH3

CH3 H

7,9-dimethylbenz[c]acridineC19H15N MW- 257.120

13 DBE

AcridineC13H9N MW- 179.073

10 DBE

CarbazoleC12H9N MW- 167.073

9 DBE

ElipticineC17H14N2 MW- 246.115

12 DBE

7H-dibenzo[c,g]carbazoleC20H13N MW- 267.104

15 DBE

Figure 4.1. Five aromatic nitrogen compounds chosen to model petroleum acidic and/or basic compounds. Five-membered ring nitrogen structures are acidic and six membered ring nitrogen species are basic.

52

nitrogen-containing ring determines the preferred ionization mechanism.

For five membered nitrogen rings, the hydrogen bonded to the nitrogen

atom is acidic and preferentially deprotonates. On the other hand, the

six membered nitrogen ring species are basic (because of the electron

lone pair on nitrogen) and efficiently protonate. Thus, two of the model

compounds are basic; two are acidic; and the remaining compound

(ellipticine) has both acidic and basic moieties.

The negative-ion APPI FT-ICR mass spectrum (Figure 4.2) of an

equimolar solution of all five nitrogen compounds in deuterated toluene

shows ions only for the acidic species. No radical anions (M-�) appear.

Under continuous APPI source operation, the mass spectrometer was

reconfigured for positive ion detection (Figure 4.3). All five nitrogen

model compounds yield positive ions by APPI. The pyrrolic compounds

(carbazole and 7H-dibenzo[c,g]carbazole) primarily form radical cations,

M+� (Table 4.1), whereas the pyridinic compounds (acridine and 7,9-

dimethylbenz[c]acridine) protonate to form (M + H)+. Ellipticine, which

contains both a pyrrolic and a pyridinic moiety, preferentially forms (M +

H)+. Table 4.1 list the ion relative abundances for each compound, and

the parenthetical values are the percentages of M+�, [M + H]+ and [M + D]+

for each compound. For the pyridinic species, the percent abundance of

[M + D]+ was 10-15 (see upper left inset in Figure 4.3). In contrast, there

was no detectable (M + D)+ for the pyrrolic class compounds (which did

form (M + H)+ in low abundance). Interestingly, 7H-dibenzo[c,g]carbazole

exhibited minor hydrogen-deuterium exchange [C20H12D1N1]+� (see Figure

4.3). Carbazole also participates in hydrogen-deuterium exchange, but

in low relative abundance.

53

m/z280270260250240230220210200190180170160

N

-N

N

CH3

CH3

-

N -

H

H

H

- H

- H

- HNegative Ion

APPI 9.4 Tesla FT-ICR MS

In C7D8

Figure 4.2. Negative ion APPI FT-ICR mass spectrum of an equimolar solution of the model compounds of Figure 4.1 in deuterated toluene. Only the acidic compounds containing a pyrrole ring are deprotonated to yield [M - H]- ions, none of which contained deuterium.

54

Table 4.1. Positive-ion APPI FT-ICR MS ion relative abundances for the five aromatic nitrogen compounds of Figure 4.1. Parenthetical values show the percentages of M+�, [M + H]+, and [M + D]+ for each compound.

Compound M+� (M + H)+ (M + D)+

Carbazole 2.7 (87) 0.4 (13) -- Acridine 0.4 (1) 39.0 (84) 7.0 (15) Ellipticine 0.8 (5) 14.8 (85) 1.8 (10) 7,9-dimethylbenz- [c]acridine 1.2 (3) 25.6 83) 4.2 (14) 7H-dibenzo- [c,g]carbazole 34.6 (99) 0.4 (1) --

Bitumen Distillation Cuts

Three Canadian bitumen petroleum distillation cuts were analyzed

by positive-ion APPI FT-ICR MS. Mass analysis (with ~100 ppb mass

accuracy) for all three cuts showed that ~90 % of the compounds contain

at least one nitrogen atom. Furthermore, the N1 class ("class" denotes

NnOoSs heteroatom composition) ions consist primarily of protonated

compounds (> 97%). Figure 4.4 shows the heteroatom class distribution

for the middle distillation cut (475-500 °C).

Unlike electrospray ionization sources,36, 58 atmospheric pressure

chemical ionization,37 or field desorption ionization,41 the APPI source

produces both positive and negative ions simultaneously. Figure 4.5

shows broadband APPI positive- and negative-ion mass spectra for the

middle distillation cut. Both spectra were collected without ion source

interruption by reversing dc voltage polarity for ion transfer and

trapping.

55

m/z280270260250240230220210200190180170160

N

+ H+

N

H

+�

m/z181.092181.086181.080

[C12H9N113C + H]+

[C13H9N1 + D]+

N

N

CH3

CH3 H

+ H

+

N

CH3

CH3

+ H

+

N

H +�

[C19H13N113C] +�

[C20H13N1 + H]+

[C20H12D1N1]

m/z268.12268.11268.10

+�

Positive Ion APPI

9.4 Tesla FT-ICR MS

In C7D8

Figure 4.3. Positive ion APP FT-ICR mass spectrum of an equimolar solution of the model compounds of Figure 4.1 in deuterated toluene. All five compounds yielded positive molecular (M+�) or quasimolecular ([M - H]-) ions. The compounds containing a six-membered pyridinic ring are sufficiently basic to readily protonate (or deuterate) (along with ~1% of radical molecular radical cations), whereas the more acidic compounds containing a five-membered pyrrolic ring form molecular radical cations, and <1% protonation (or deuteration). For the even-electron species, the extent of deuteration was ~15% for acridine (see the mass scale-expanded inset spectrum), ~10% for ellipticine, and ~14% for 7,9-dimethylbenz[c]acridine. Also, at nominal mass 268 (right mass scale-expanded inset), 7H-dibenzo[c,g]carbazole exhibits slight hydrogen-deuterium exchange.

56

Deuteration versus Protonation

The Canadian bitumen middle distillation cut was dissolved in

deuterated toluene and mass analyzed. The deuterated toluene sample

produce a relative class distribution (not shown) identical to that for the

toluene sample (Figure 4.4). Due to the sample complexity (~2000

molecular species in a 400 Da mass window), the ultrahigh resolving

power of FT-ICR mass spectrometry was essential to resolve and identify

the deuterated species. Figure 4.6 is the a mass scale-expanded

segment from the bitumen broadband positive-ion mass spectrum. The

2.9 mDa mass difference between the two compounds that differ

elementally by 13CH versus CD requires a minimum mass resolving

power of 160,000 (m/∆m50%, in which ∆m50% is the mass spectral peak

full width at half-maximum peak height). Furthermore, the 1.5 mDa

mass difference between H2 and D requires a minimum mass resolving

power of 300,000. Additional mass doublets unique to APPI mass

spectra arise by virtue of the presence of radical molecular cations and

(de)protonated compounds: namely, 4.5 mDa separation66 for 13C of M+�

vs. 12CH of [M + H]+ and 1.5 mDa separation for H2 of M+� vs. D of [M - H2

+ D]+. All of the above mass doublets could be resolved by FT-ICR mass

spectrometry at an average mass resolving power of 500,000 for the

seven assigned spectral peaks in Figure 4.6.

It is thus possible to quantitate the relative abundances of

deuterated ([C33H49N1 + D]+) vs. protonated ([C33H49N1 + H]+) ions

identified in Figure 4.6. For the spectral segment in Figure 4.6, as well

as the mass spectrum as a whole, the detected deuterated ions

contributed ([M + D]+ vs.[M + H]+) ≈ 5% for the even electron N1 class

compounds. For other less abundant protonated species, the deuterated

species if present were below the detection limit.

57

N1 N1

O1

N1

S1

O1

S1

S1 S2 HC

Athabasca

Bitumen Distillation Temperature

475 – 500 °C

m/z680640600560520480440400360320280

(+)APPI FT-ICR MS1801 Elemental Formulas

RMS Mass Accuracy

149 ppb

Figure 4.4. Heteroatom class distribution for a bitumen mid-range distillate

positive ions. Each class represents the relative ion abundance of species which contain the stated heteroatom(s) in the assigned molecular formula. The error bars are standard deviation computed from 3 separate sample preparations and analysis.

58

m/z700660620580540500460420380340300260

Positive Ions

Negative Ions

Athabasca

Bitumen

APPI FT-ICR MS

Distillation Temperature

475 – 500 °C

Figure 4.5. Broadband APPI FT-ICR mass spectra of a bitumen mid-range distillate. The positive- and negative-ion spectra were collected without source interruption and with appropriate instrument polarity changes. Although APPI produces both molecular radical cations (M+�) as well as [M - H]- and [M + H]+ ions, the N1 class positive-ion mass spectrum is dominated (~97%) by protonated compounds.

59

Negative and Positive Ion Class Distribution Comparison

Unique elemental compositions were assigned to both negative and

positive ion mass spectral peaks based solely on accurate mass

measurement67 combined with sorting of homologous alkylation series34,

35 to yield 1844 negative-ion elemental compositions with an rms mass

error of 105 parts-per-billion, and 1801 positive-ion elemental

compositions with an rms mass error of 149 parts-per-billion. Figure 4.7

displays the heteroatom classes for positive- and negative-ion APPI FT-

ICR mass spectra. The elemental compositions for each class can be

further sorted by DBE (double bond equivalents, in which DBE is the

number of rings plus double bonds calculated from Eq. 4.1)

Double Bond Equivalents (CcHhNnOoSs) = c -h/2 + n/2 + 1 4.1

Representative structures for the most abundant DBE components of the

most abundant (N1) class compounds are illustrated. Each molecular

structure represents one of many possible isomers. Neverthelss, we can

say that the nitrogen atom DBE 9 N1 class positive ion resides in a six

membered pyridinic ring.

Conclusions

APPI of the nitrogen class compounds in a petroleum sample

preferentially forms ions by means of proton transfer reactions. The

Athabasca bitumen N1 class positive ions consist of >97 % protonated

compounds and only ~3 % radical molecular cations. Based on their

elemental compositions, all of the negative ions form by deprotonation of

60

m/z

461.45461.43461.41461.39461.37461.35

[C32H49N113C + H]+

[C33H49N1 + D]+

[C33H51N1]+�

2.9 mDa 13CH vs. CD

1.5 mDa H2 vs. D

[C30H50O1S1 + H]+

[C33H48O1 + H]+

[C31H45N1O113C + H]+

[C32H48N2 + H]+

Athabasca Bitumen


475 – 500 °C

Positive Ion APPI 9.4 Tesla FT-ICR MS

In C7D8

Figure 4.6. Positive-ion APPI FT-ICR mass scale-expanded segment of a bitumen mid-range distillate in deuterated toluene. This figure emphasizes the ultrahigh resolving power required to resolve the deuterated species in complex petroleum mixtures.

61

N1 N1

O1

N1

S1

S1 S1

O1

S2 O2 S1

O2

N1 O1 O3

Positive Ions Negative Ions

Acid Species

Proton DonorsBasic Species

Proton Acceptors

(CH2)n(CH2)n

9 DBE 3 DBE

N

O

OH

Athabasca Bitumen


475 – 500 °C

APPI 9.4 Tesla FT-ICR MS

Figure 4.7. Heteroatom class distribution for the positive and negative ions from a bitumen mid-range distillate. Generic structures are shown for the most abundant positive and negative species. DBE is the number of rings plus double bonds, and is calculated from Eq. 4.1. Because only ~5% of the even-electron N1 class ions contain deuterium, the acidic neutrals in the original sample are likely proton donors to form the even-electron species from basic neutrals.

62

precursor neutrals. Aromatic nitrogen model compounds (Figures 4.2

and 4.3) exhibit similar ionization trends in which the majority of

nitrogen species are ionized through proton transfer reactions (Table

4.1). Although pyrrolic species more efficiently form negative ions and

pyridinic species positive ions, pyrrolic species can also form radical

cations (M+�). Interestingly, the more aromatic pyrrolic compound

(7H-dibenzo[c,g]carbazole) exhibited higher ion abundance (radical

cation) than carbazole, suggesting that a more condensed aromatic core

structure can add stabilty to a radical cation.

Negative and positive ions form simultaneously in the APPI source,

and therefore, there are many potential proton donors including toluene

(or deuterated toluene) solvent. However, in the present bitumen sample,

deuterated toluene donated a deuteron to only 10-15 % of the

even-electron ions formed from pyridinic nitrogen model compounds.

Presumably, the proton donors for the pyridinic nitrogen compounds (for

the model nitrogen compound spectra) are the pyrrolic (acidic) nitrogen

compounds from the sample itself (even though the toluene dopant is

present at orders of magnitude higher concentration).

For the petroleum sample, only 5 % of the even-electron nitrogen

class species were deuterated. The most abundant negative-ion species

is the O2 class, likely carboxylic acids. All species detected in the

petroleum negative-ion spectrum were [M - H]-. Reasonably, the even

electron nitrogen class that were protonated (not deuterated) are

protonated through reactions with acidic species present in the sample.

63

CHAPTER 5. SULFUR SPECIATION OF PETROLEUM BY ATMOSPHERIC PRESSURE PHOTOIONIZATION FOURIER

TRANSFORM ION CYCLOTRON RESONANCE MASS SPECTROMETRY

Summary

A Middle East petroleum and its Saturates-Aromatics-Resins-

Asphaltenes (SARA) fractions are analyzed by Atmospheric Pressure

Photoionization (APPI) with a 9.4 Tesla Fourier transform ion cyclotron

resonance (FT-ICR) mass spectrometer. The Environmental Protection

Agency has regulated the heteroatom content in petroleum products to

low levels (<15 ppm) to reduce harmful combustion products and enable

clean vehicle technologies to operate optimally. Sulfur is the third most

abundant element in petroleum, and non-polar sulfur containing

compounds are not efficiently ionized by electrospray ionization. APPI is

a more general ionization technique which can ionize hydrocarbons and

non-polar sulfur compounds through proton transfer reactions (dopant-

assisted APPI) and charge exchange. In this current work, we speciate

the sulfur containing aromatic compounds in an unfractionated

petroleum and also its SARA fractions and note differences and

similarities between the sulfur species in the samples.

Introduction

Since the discovery of petroleum at Oil Creek in Titusville,

Pennsylvania, 1859,68 and the subsequent industrial revolution,

societies’ dependence on petroleum products has increased. The

consumption of "sweet" crude oil reserves has lead to an increase in the

refinement of less desirable heavy crude oil reservoirs indicated by a

steady trend in the feed stock crude oil in the United States toward lower

64

API gravity (heavier crude oils) and higher sulfur content.31 The average

sulfur content of all crude oils refined in the five regions of the U.S.

increased from 0.89 wt.% in 1981 to 1.25 wt.% in 1997, while the

corresponding API gravity decreased from 33.74◦ in 1981 to 31.07◦ in

1997.69

The United States Environmental Protection Agency (EPA) is

charged with regulatory authority over the petroleum industry. More

stringent EPA regulations have created a need to develop technologies

designed to remove harmful heteroatoms. More specifically, sulfur (the

third most common element in crude oil) content in petroleum products

has been regulated to lower levels and ultra low level by year 2010.28-30

Moreover, large oil reserves in the Middle East and Venezuela have high

sulfur content (>1%).70

Initially, diesel fuel sulfur content was targeted primarily because

of acid rain and SO2 pollution. Oil fractions in the diesel boiling range

typically contained 0.1 to 1.5 weight percent sulfur, and as late as the

1980s, sulfur specifications for diesel oils were decreased to 0.3 wt % or

3000 parts per million (ppm).71 In the 1990s, EPA regulations (Clean Air

Act, Code of Federal Regulations, Title 40) and European standards were

enacted to reduce the sulfur content in diesel fuel to 15 ppm by 2007

and 10 ppm by 2009 respectively from the current standard of 500

ppm.71

Diesel is not the only fuel affected by EPA regulations. The EPA's

Tier 2 Vehicle and Gasoline Sulfur program treats vehicles and the fuels

they use as a system. Thus, clean vehicle technologies will require low-

sulfur gasoline for vehicles to run their cleanest.28-30 This program

requires the refinery industry to meet a 30 ppm sulfur content average

with an 80 ppm sulfur cap.

Prior high resolution mass spectrometric applications have focused

on the characterization of polar compounds in crude oils, bitumens and

their SARA isolated fractions by Electrospray Ionization (ESI) FT-ICR

65

mass spectrometry.32, 33 The selectivity of the ESI process efficiently

ionizes acidic and basic species without interference from the bulk

hydrocarbon matrix. However, less polar sulfur containing species are

rendered unobservable due to their low ionization efficiency.

Furthermore, polar sulfur species are often overwhelmed by the more

abundant polar species of equal acidity/basicity or less abundant species

of greater acidity/basicity and, therefore, are present at low signal to

noise.

Atmospheric Pressure Photoionization (APPI) selectively ionizes

those species that can either undergo direct ionization from 10eV

photons (aromatics) or gas phase proton transfer reactions and charge

exchange reactions.19, 21, 23 The benefit of APPI is that it efficiently ionizes

many important classes (nonpolar sulfur species and polycyclic aromatic

hydrocarbons (PAH’s)) that are unobservable by ESI. In this work, we

focus on the compositional characterization of both nonpolar and slightly

polar sulfur species in SARA fractions isolated from a medium Middle

Eastern crude oil and the whole crude by APPI FT-ICR MS to provide

insight into nonpolar sulfur compositional variations in the whole crude.


Middle East Crude Oil

A Middle East Crude oil was supplied by ExxonMobil, and a

sample was fractionated according to the Saturates-Aromatics-Resins-

Asphaltenes (SARA) method.57 The crude oil (1 gram) was added to 100

mL of n-heptane. After stirring 4 hours, the solution was stored in the

dark for ~12 hours. The solution was then filtered to collect the n-

heptane-insoluble asphaltenes. Subsequent Soxhlet extraction (8

min/cycle with hot normal heptane) removed coprecipitant materials

from the purified asphaltenes. The raw asphaltene was purified until the

66

hot normal heptane collected in the extraction region of the Soxhlet

apparatus was uncolored. The maltene fraction was further separated

into saturates, aromatics and resins.57 An aliquot of the whole crude

and SARA fractions were diluted (500 µg/mL) in toluene (Fisher HPLC

grade) and analyzed without further preparation.


Middle East Crude Analysis

Previous mass spectral analysis revealed the complexity of data

that can result from petroleum analysis with an APPI source (Chapter 2).

Crude oil fractionation methods have been developed to lessen the

complexity of a sample. A common method used for petroleum analysis

is the Saturates-Aromatic-Resins-Asphaltenes fractionation. The

challenge for mass spectrometry of complex mixtures is resolving power.

For FT-ICR mass spectrometry, the many components of petroleum,

though challenging, can be identified in part because of the ultra-high

resolving power afforded by ICR mass spectrometers without sample

fractionation. Furthermore, high mass accuracy can yield unique

elemental formulas for mass spectral peaks. Nevertheless, in this work,

we employ a common SARA fractionation method before FT-ICR mass

analysis for a Middle East crude oil to speciate the sulfur compounds

and identify differences between the fractions and whole crude.

Figure 5.1 is a comparison of the broadband mass spectra of the

whole crude oil and its SARA fractions. The aromatic and resin fractions

display similar mass spectral distribution while the saturate fraction

distribution is shifted to lower mass and the asphaltene fraction to

higher mass. This broad perspective agrees with the common mass

characteristics for the SARA fractions, i.e., the saturates are considered

67

Figure 5.1. Broadband positive APPI FT-ICR mass spectra of the whole crude and its SARA fractions. The samples were analyzed at the same concentration and experimental conditions.

68

the lighter fraction, and the asphaltenes are more polycondensed

aromatic structures and heavier, with the aromatics and resins in-

between the light and heavy species.

Unique elemental formulas were assigned to spectral peaks based

on accurate mass and homologues series. The summed relative

abundance of all the spectral peaks assigned to a homologues series can

be represented in a bar graph (Figure 5.2). In Figure 5.2, the class, e.g.

S1, relative abundance represents the summed spectral magnitude for all

peaks assigned a elemental formula with only one sulfur atom and the

remainder of the elemental formula composed of only carbon and

hydrogen. Middle East crude oils have a high sulfur content and this is

reflected in the whole crude analysis (Figure 5.2). Eight of the eleven

classes above 1 percent summed relative abundance contain one or more

sulfur atoms.

S1 S2 N1 N1

S1

HC O1

S1

S3 N1

O1

N1

S2

N1

O1

S1

O1

S2

+ APPI FT-ICR MS

Class Distribution

Unfractionated Middle East Crude Oil

Class

Re

lati

ve

Ab

un

da

nc

e

Figure 5.2. Summed relative ion abundance for heteroatom classes in the whole crude. Middle East crude oils have a high sulfur content. The graph includes those heteroatom classes above 1% relative abundance. Eight of the eleven classes contain one or more sulfur atoms.

69

Figure 5.3 is the class analysis of the four SARA fractions obtained

from the Middle Eastern crude oil by positive ion APPI FT-ICR MS. The

saturate fraction (upper left) is dominated by the S1 and S2 classes and

contains a high amount of the hydrocarbon (HC) class as well. The

aromatic fraction (upper right) continues the high S1/S2 trend, and also

contains a high amount of S3 and NS classes with a increased amount of

Ox species. The resins (bottom left) transition from high Sx classes to

high NO, NOS and OS classes but also contain the S1, S2 and S3 classes

observed in the aromatics. The asphaltene fraction reverts back to

classes similar to those observed in the aromatic fraction with a large

associated increase in the OSx and NxOx and NxSx classes.

Summed relative abundance bar graph analysis is informative for

heteroatom type distribution, but contains no information that pertains

to aromaticity (DBE) and carbon number. Figure 5.4 is a three-

dimensional relative abundance contoured DBE versus carbon number

plot for selected heteroatoms classes of the whole crude and its SARA

fractions. The x-axis represents carbon number and the y-axis DBE.

The z-axis is color scaled to relative ion abundance (all plots are scaled

equally). This type of information format represents a complete picture

of all elemental formula assignments for the class.

The carbon number distributions (x-axis) for the whole crude and

its SARA fractions are similar in Figure 5.4. In general, the DBE range of

the whole crude is duplicated in the individual SARA fractions. However,

the higher DBE species are not efficiently ionized for the whole crude but

are apparent in the asphaltene fraction.

For the S1 class, the saturate plot species exhibit relatively low

DBE and carbon number which progress to species higher in DBE and

carbon number through the aromatics and resins with the highest

DBE/carbon-number species seen in the asphaltenes. This trend is also

repeated for the S2, S3 and N1S1 species.

70

S2

S1

S3

O1

S2

O1

S1

N1 O

1 S

1

N1 S

1

N1

O1

N1 S

2

O1

S4

N1

O1

S3

HC

O2

S1

N1 O

1 S

2

N1

O2

N1 S

3

N1 O

2 S

1

N1 O

2 S

4

O2

S2

O2

N2 O

1 S

1

N1

O1

N1

O1

S1

S1

N1

N1 S

1

S2

O1

S1

O2

O1

S2

HC S3

N1

O2

O1

N1 S

2

N1 O

1 S

2

N1 O

2 S

1

O2

S1

N2 O

1 S

1

N2 S

1

O2

S2

O1

S3

N3 S

1

S2

S1

N1

N1 S

1

S3

HC

N1

O1

O1

S1

O1

S2

N1 S

2

N1

O1

S1

S4

O1

O1

S3

O2

S1

S1

S2

HC

O1

S1

N1

O1

N1 S

1

S3

O1

S2

O2

S1

O2

N1 O

1

Saturates

Resins Asphaltenes

Aromatics

2

4

6

8

10

12

5

10

15

20

25

30

40

35

2

4

6

8

10

12

18

14

16

5

10

15

20

25

Class

Ab

so

lute

Ab

un

da

nc

e,

Arb

itra

ry U

nit

s

Figure 5.3. Summed relative ion abundance class graphs for the SARA fractions. The saturate, aromatic, and asphaltene fractions show sulfur species most abundant. For the resins, more polar heteroatom classes are dominant.

71

Figure 5.4. Three-dimensional relative abundance contoured DBE versus carbon number plot for

selected heteroatom classes of the whole crude and its SARA fractions. Carbon number is represented on the x-axis and double bond equivalents (equation 1.19) on the y-axis. The z-axis is color scaled to relative ion abundance. All plots are scaled equally.

72

Furthermore, the resin fraction has a lower abundance of sulfur

species. This is also represented in the class distribution graph (Figure

5.3). The resins are dominated by more polar species with nitrogen and

oxygen heteroatoms. Additionally, the saturates are deficient in the S3

and N1S1 species. The N1S1 and S3 species are found primarily in the

aromatic and asphaltene fractions.

Conclusions

APPI ionizes the non-polar species in crude oil which are not

efficiently ionized by ESI sources. There is a need to better understand

the complex matrix of crude oil. APPI coupled to FT-ICR MS can provide

elemental formula analysis for the whole crude oil without fractionation.

The SARA fractionation method separates the components of crude oil

into subgroups based on aromaticity and polarity. However, there is a

significant bleed-over between the fractions. That is to say, the same

elemental species are observed in more than one fraction (although

structural differences may be present). Nevertheless, the most abundant

species of each fraction are significantly different (DBE and carbon

number) from other fractions. For any single class, an overlap of the

same elemental assignments are found in the whole crude analysis,

albeit at different relative abundances. After fractionation, the relative

ion abundances increase for species that dominate that fraction. We

postulate that the differences in peak spectral magnitude between the

whole crude and its fractions can be partially attributed to the ratio of

photon flux to species molar concentration and competitive ionization in

the APPI source.

I have presented a detailed analysis of the non-polar sulfur

components for a Middle East crude oil. Further studies will investigate

the elemental differences between crude oil samples at different catalytic

hydrodesulfurization steps.

73

CHAPTER 6. LIMITATIONS OF AROMATIC SULFUR CHEMICAL DERIVATIZATION ANALYSIS OF PETROLEUM BY ESI AND APPI FOURIER TRANSFORM ION CYCLOTRON RESONANCE MASS

SPECTROMETRY

Summary

Sulfur-containing compounds in petroleum are detrimental to the

environment and refining processes. The molecular characterization of

the sulfur-containing species is therefore an important subject. One

characterization method is the derivatization of the sulfur species prior to

Electrospray Ionization (ESI) mass analysis. However, Atmospheric

Pressure PhotoIonization (APPI) mass analysis can provide molecular

characterization without chemical derivatization. A recent report

speciated the sulfur-containing compounds in a vacuum bottom residue

and identified the most abundant sulfur compounds present with

double-bond-equivalents (DBE) values between 4 and 12. Our extensive

experience with heavy-end petroleum causes us to question the

analytical technique of sulfur derivatization prior to mass analysis. Here,

we investigate the sulfur speciation of a petroleum vacuum bottom

residue by ESI and APPI coupled to a 9.4 Tesla Fourier transform ion

cyclotron resonance (FT-ICR) mass spectrometer. A comparison of the

sulfur-containing compounds between the methods reveals significant

differences in sulfur species DBE values. We postulate differences in

APPI ionization efficiency could account for the DBE discrepancy.

However, an analysis of the saturate and aromatic fraction by APPI

shows equal ionization efficiency across a broad DBE range.

Furthermore, we conclude the methylation reaction is sterically hindered

for large DBE species (> 20 DBE).

74

Introduction

Despite the recent interest in renewable energy sources, fossil fuels

are projected to be the major source of energy for the next fifty years.72

The increase in global consumption of "sweet" crude oil reserves has led

to an increase in the refinement of less desirable heavy crude oil

reservoirs, as evident by a steady trend in feed stock crude oils in the

United States toward lower API gravity (heavier crude oils) and higher

sulfur content.31 The heavier feed stocks, heavy oils and bitumens,

contain a large weight percent of sulfur, nitrogen and oxygen

heteroatoms. The heteroatoms in the heavy petroleum are harmful to

the environment, are detrimental to hydrogen addition and carbon

rejection processes in petroleum refineries and therefore must be

removed.72

Even before the current need for low sulfur petroleum products,

the refining industry had employed hydrodesulfurization for other

reasons, e.g., to decrease corrosion, increase gasoline stability, and

decrease smoke formation in kerosene.72 Therefore, the petroleum

industry has significant experience in desulfurization processes but

primarily for lighter feed stocks. With current feedstock trends and a

desire to process atmospheric and vacuum bottom residue into

marketable lighter petroleum products, there is a need to develop new

refining technologies and processing methods better suited for the

heavier feedstocks and residues.

Crude oil is a complex mixture of hydrocarbons with varying

amounts of nitrogen, sulfur, oxygen and trace amounts of metal (iron,

nickel and vanadium). An industry standard for the bulk

characterization of crude oil is through the study of its fractional

components. However, the fractional compositions vary significantly

with laboratory isolation procedures; especially for heavier feed stocks.73

In order to develop more efficient refining processes for heavier petroleum

75

feedstocks and residues, mass spectrometry can provide detailed

compositional information on whole crude oils. Specifically, Fourier

transform ion cyclotron resonance (FT-ICR) mass spectrometry is capable

of resolving >12,000 spectral peaks in a single spectrum (which is

paramount for petroleum) and provide unambiguous molecular

elemental formulas based on mass accuracy and homologue series.66

Electrospray ionization coupled to FT-ICR has provided elemental

formula composition for the polar constituents in petroleum.32, 33 Acidic

molecular species, e.g., compounds with carboxylic acid or sulfonic acid

groups, are deprotonated and basic species, e.g., pyridinic nitrogen, are

protonated in the ESI process to form charged species. However, sulfur

compounds (which are not sufficiently acidic or basic) and hydrocarbons

are not efficiently ionized by ESI. One possible

analytical/characterization method for non-polar sulfur species is ESI

mass spectrometry of derivatized sulfur compounds. The derivatization

chemistry involves electrophilic attack on the heterocyclic sulfur by a

strong alkylating (methylating) reagent forming S-alkyl (methyl)

sulfonium salts in solution prior to the ESI process. However, an

alternate analytical method is Atmospheric Pressure PhotoIonization

(APPI). APPI can efficiently ionize gas phase non-polar species (and polar

species) through direct photon ionization19, 21 or proton transfer (with a

toluene dopant23 or proton transfer reactions with acid species in a

complex mixtures74) and charge exchange reactions. Thus, APPI

precludes the need for derivatization.

Recently, sulfur derivatization of a vacuum bottom residue and ESI

FT-ICR MS analysis was reported.75 The analysis provided elemental

molecular characterization of a feed stock (~900 species) before

hydroprocessing and an effluent (~1000 species) after hydroprocessing.

The derivatization was preceded by a saturates-aromatics-resins-

asphaltene (SARA) fractionation and a ligand exchange chromatographic

procedure to enrich sulfur species. The results indicated that the bulk of

76

the sulfur compounds for the feedstock and effluent of the vacuum

bottom residue exhibited Double Bond Equivalents (DBE, a value equal

to the number of ring plus double bonds in the molecular structure

calculated from the elemental formula) between 4 and 12. However, from

our experience with vacuum residues and heavy crude oils, the reported

DBE ranges for the sulfur-containing species were much lower than

previously observed by APPI and lower than expected for species

concentrated in a vacuum residue. In this report, we utilize ESI and

APPI coupled to a 9.4 Tesla FT-ICR mass spectrometer to speciate the

sulfur-containing compounds in a vacuum bottom residue and identify

similarities and/or differences in the species identified between the

ionization techniques. We then compare the results (ESI and APPI) of the

chemically derivatized vacuum bottom residue to highlight limitations of

the derivatization process.


Vacuum Bottom Residue

Methyliodide, silver tetrafluoroborate, 1,2-dichloroethane,

methylene chloride and acetonitrile were purchased from Sigma-Aldrich

(high purity, St Louis MO.). Established methodology was adopted for

the derivatization chemistry.75-77 A sample of the Canadian bitumen

residue (13.5 mg) was dissolved in a (conical) vial containing 1,2-

dichloroethane (3 mL), methyl iodide (1 mmol) and a stir bar. While

mixing, a solution of silver tetrafluoroborate (1 mmol) in 3 ml of 1,2-

dichloroethane was added. A yellow-brown precipitate immediately

formed upon addition. The solution was stirred vigorously on a magnetic

stir plate at ambient temperature for 48 hours. The precipitate was

filtered and further washed with 1,2-dichloroethane. The combined

washings and filtrate were evaporated to dryness under reduced pressure

77

to remove solvent and excess methyl iodide. The methylated samples

were re-dissolved in a 1:1 (v/v) solution of methylene

chloride/acetonitrile (10 mg/ml stock solution) for ESI analysis (1mg/mL

analysis concentration). The stock methylated solution was diluted (1:10)

into toluene for APPI analysis. Untreated residue was prepared (1mg/mL

in 60:40 toluene : methanol and 1% formic acid) for ESI analysis and

APPI analysis (1 mg/mL in toluene).

SARA Fractionation

Solvents were purchased from Fisher Chemical (HPLC grade). A

SARA fractionation57 of the vacuum bottom residue (VBR) was

accomplished (517.1 mg). The sample was mixed with n-heptane (50

mL), stirred with a magnetic stir bar for 90 minutes and stored in the

dark overnight. A Whatman No. 1 filter paper was used to separate the

n-heptane insolubles (asphaltenes) from the maltenes and the filter

paper asphaltenes were dried at room temperature. The maltenes

n-heptane solution was rotary evaporated to dryness under reduced

pressure. The dry maltenes were re-dissolved in n-heptane (6 mL). The

maltene solution was then adsorbed onto the surface of activated

alumina (3 g) and the maltene alumina slurry was dried while stirring

under a stream of nitrogen. A glass column (11 mm i.d. x 300 mm

length) was packed with activated alumina adsorbent (6 g) and the

adsorbed maltenes were packed on the top. In sequence, 40 mL of n-

heptane, 80 mL of toluene and 50 mL of a toluene:MeOH (8:2, v/v)

mixture were used to elute the saturates, aromatics and resins,

respectively. The eluants were rotary evaporated under reduced pressure

until dry and weighed. The recovered mass for each fraction and percent

recovered follows: saturates, 122.5 mg (23.7 %); aromatics, 150.0 mg

(29.0 %); resins, 150.1 mg (29.0 %); asphaltenes, 172.6 mg (33.4 %). The

78

saturates and aromatics were diluted in toluene (1 mg/mL) for APPI

analysis.

CHNOS Analysis

A Flash Elemental Analyzer (C.E. Elantech, Inc.) model 1112 was

used for CHNS/O weight percent determination of the vacuum bottom

residue. Quadruplicate samples (~2 mg) were weighed for the CHNS

analysis (combustion) and O analysis (pyrolysis). Calibration values were

developed using sulfanilamide and 2,5-Bis-(5-tert.-butylbenzoxazol-2-

yl)-thiophen (BBOT) standards. Percent composition follows: carbon 81.3

± 0.19 % RSD, hydrogen 9.5 ± 0.28 % RSD, nitrogen 0.75 ± 2.3 % RSD,

sulfur 5.7 ± 3.8 % RSD, oxygen 1.5 ± 3.1 % RSD.


APPI FT-ICR MS

Although crude oil is the most compositionally complex organic

mixture, ESI FT-ICR MS has enabled the detailed speciation of its polar

components.33, 48 Atmospheric Pressure PhotoIonization (APPI) can

produce ions from non-polar sulfur-containing petroleum compounds

and when combined with the ultra-high mass resolving power and

unmatched mass accuracy of FT-ICR MS, sulfur speciation of petroleum

is achieved. Petroleum fractionation methods can be employed to lessen

the sample complexity and, even though the previous report75

fractionated a vacuum bottom residue (VBR) before mass analysis, our

attention is initially focused on the analysis of the raw VBR (a less

complicated sample preparation) and the raw methylated VBR by ESI

and APPI coupled to a 9.4 T FT-ICR MS.

79

Raw Vacuum Bottom Residue

The residue analysis (raw unmethylated) yielded approximately

5800 and 2000 unique elemental formulas for positive ion APPI and ESI

respectively. The elemental formulas were sorted by class, DBE and

carbon number. Figure 6.1 represents the summed relative abundances

of each class above 1 % relative abundance. The nitrogen class is the

most abundant for both ionization techniques. ESI efficiently ionizes the

basic pyridinic N1 class78 at twice the relative abundance as the APPI N1

class. For other polar classes, e.g., N1S1 and N1O1, the relative ionization

efficiency for the two ionization methods is comparable. For the non-

polar species, e.g., S1, S2, HC (hydrocarbon), only APPI produced spectral

signal.

Relative class abundance graphs are sufficient representations of

class distribution but contain no information about carbon number and

DBE distribution. One format that represents carbon number and DBE

distribution within a class is an iso-abundant contoured DBE versus

carbon number plot. Figure 6.2 compares the ESI and APPI carbon

number and DBE distribution for the S1 and N1S1 classes of the raw

VBR. Carbon number is plotted along the x-axis and DBE on the y-axis.

The relative ion abundance within each class is color scaled in the z-axis.

The APPI S1 class has a carbon distribution of 22≤C#≤45 and more

interestingly, a DBE distribution of 6≤DBE≤35. The greatest magnitude

spectral peaks for the APPI S1 have DBE values between 20 and 30. In

comparison, the ESI and APPI N1S1 classes have similar magnitude in

the lower DBE range, however, the APPI N1S1 class DBE range extends to

higher DBE (similar to the APPI S1 class). Similarly, other mutually

common classes (ESI and APPI Figure 6.1) display comparable DBE and

carbon number range for the greatest spectral magnitude ions with APPI

generated species extending to higher DBE. Hence, for the raw

unmethylated VBR, mutually ionized species have similar DBE range

80

ESI / APPI Class Distribution Comparison

Raw Vacuum Bottom Residuum

Class (>1% R.A.)

Su

m R

ela

tive A

bu

nd

an

ce

0

5

10

15

20

25

30

35

40

45

50

N1

N1

S1

S2

N1 O

1

S1

N1

S2

S3

HC

N1

O1

S1

N2

O1

S2

O1

S1

N2

S1

O1

S4

N2 O

1

APPI

ESI

Figure 6.1. Heteroatom class distribution for the raw vacuum bottom residue (not methylated). All classes ionized by ESI and APPI above 1 % relative abundance are represented. The non-polar classes, e.g., S1, S2 and HC (hydrocarbon), were not detected by ESI. APPI analysis detected both the polar and non-polar species.

81

Figure 6.2. Iso-abundant contoured DBE versus carbon number images for heteroatom species of the raw vacuum bottom residue. Relative ion abundance within the class is color scaled in the z-axis. The ESI and APPI N1S1 classes have similar carbon number distributions. However, the DBE distribution for the APPI N1S1 image extends to higher DBE. The non-polar S1 species was not detected by ESI.

82

which suggest the polar species generated by either ESI or APPI are

equally represented.

Raw Methylated Vacuum Bottom Residue

An identical positive-ESI and APPI FT-ICR MS analysis was

performed on the methylated raw vacuum bottom residue. Figure 6.3 is

the class distribution for the methylated sample. For the ESI classes,

there is a dramatic shift in highest relative abundance from the N1 class

(Figure 6.1) to the S1 class. Furthermore, the methylation reaction

formed hydrocarbon (HC) and O1 class ions not previously detected in

the raw VBR ESI data. The ESI O1 class most likely contains furanic

structures that are known to also react with the derivatization reagent

forming oxonium ions. The APPI class distribution (Figure 6.3) is nearly

identical to the raw (underivatized) VBR in Figure 6.1.

Figure 6.4 is the iso-abundant contoured plots for the methylated

APPI and methylated ESI data for the S1 and N1S1 classes. The APPI S1

and N1S1 images are similar to those in Figure 6.2 (unmethylated VBR),

with the exception of slightly lower DBE values present in the APPI raw

VBR S1 image are absent in the methylated VBR. For example, the APPI

raw VBR S1 class begins at DBE 8 (Figure 6.2) and for the APPI

methylated VBR, the S1 DBE range begins at 13. Also, the ESI N1S1

image (Figure 6.4) is comparable (in the most abundant DBE and C#) to

the ESI N1S1 image in Figure 6.2. However, the differences between the

ESI S1 class and the APPI S1 class in the derivatized VBR sample are

remarkable. Although the carbon number distributions are similar, the

DBE distributions are well separated with little overlap. We postulate a

number of possible explanations for the DBE distribution discrepancy

between the S1 species.

83

ESI / APPI Class Distribution Comparison

Methylated Raw Vacuum Bottom Residual

Class (>1% R.A.)

Su

m R

ela

tive A

bu

nd

an

ce

0

5

10

15

20

25

30

35

40

N1

N1

S1

N1

O1

S1

HC

S2

N1

O1

S1

N1

S2

O1

N2

O1

S1

N1 O

2

S3

O2

O1

S2

APPI

ESI

Figure 6.3. Heteroatom class distribution for the raw methylated vacuum bottom residue. All classes ionized by ESI and APPI above 1 % relative abundance are represented. The ESI distribution exhibits a remarkable change in highest relative abundance to the S1 class. The S2, HC and O1 classes are also detected by ESI in the methylated sample. The APPI heteroatom class distribution is similar to Figure 6.1.

84

Figure 6.4. Iso-abundant contoured DBE versus carbon number images for heteroatom species of the raw methylated vacuum bottom residue. Relative ion abundance within the class is color scaled in the z-axis. The N1S1 images are similar to the images produced from the unmethylated sample (Figure 6.2). However, the S1 class images differ dramatically between ESI and APPI. The low DBE species in the ESI S1 image are absent in the APPI image.

85

One possible cause is that APPI more efficiently ionizes larger DBE

species and thereby biases the DBE images to high values. In fact, it is clear

from the ESI methylated VBR data that lower DBE species are present in the

raw vacuum bottom residue. However, the APPI S1 DBE distribution for the

VBR does not reflect the lower DBE S1 species. This issue will be addressed in

the next section. Another possibility is that the methylation reaction is

sterically hindered for larger DBE species. Thus, the low DBE S1 species could

represent only a small fraction (low mass fraction) of the total raw VBR sulfur

species but be highly abundant in the ESI mass spectral results due to their

inequitable methylation efficiency (compared to high DBE S1 species) in the

derivatization step.

Saturate and Aromatic Fraction of the Vacuum Bottom Residue

To test whether APPI more efficiently ionizes larger DBE species and

thereby biases the DBE images to high values (ionization efficiency differences

between low and high DBE S1 species), we probe the APPI ionization efficiency

for species of widely different aromaticity (DBE). The experiment is to

fractionate the VBR into its saturate and aromatic fractions and subsequently

analyze each by APPI. An equal weight combination of the saturates and

aromatics would then be analyzed to identify gross differences in ionization

efficiencies between low DBE S1 species (present in the saturate fraction) and

high DBE S1 species (present in the aromatic fraction).

Figure 6.5 is the heteroatom class distribution of the saturate, aromatic

and a combined mixture (1:1 by weight) of the saturate and aromatic fractions

analyzed by APPI. The combined saturate and aromatic solution was

86

APPI Class Distribution

Saturates and Aromatic Fractions

Class (>1% R.A.)

Su

m R

ela

tiv

e A

bu

nd

an

ce

0

5

10

15

20

25

30

35

40

N1

S1

S2

N1

S1

HC

S3

N1

O1

N1

S2

O1

S1

O1

N1 O

1 S

1

O2

S1

Saturates

Aromatics

Aromatics and Saturates

Figure 6.5. APPI analyzed heteroatom class distribution for the saturates, aromatics and a solution of saturates and aromatics fractionated from the vacuum bottom residue. The saturates and aromatic solution was an equal molar concentration prepared by mixing equal volumes of equal mass/volume solutions. All classes above 1 % relative abundance are represented.

87

prepared by mixing equal volumes of equal weight per volume solutions.

Interestingly, the saturate fraction has a high relative abundance for the

S1 class and significantly less for the N1 class. This suggests that many

sulfur species elute into the saturate fraction in a SARA isolation

procedure. As expected, the combined saturate and aromatic fractions

yield a heteroatom class distribution which is similar to the raw VBR

distribution (Figure 6.2). The S1 DBE distribution of the three solutions

is depicted in Figure 6.6. The calculated DBE values (equation 1.19) are

for the cation (not the neutral species), and therefore, a non-integer value

for protonated compounds [M + H]+ is possible because of the additional

hydrogen atom. The integer values are the result of DBE calculations for

radical molecular ions (M+�). The saturate distribution includes DBE

values normally associated with a saturate fraction, i.e., low DBE values

which can include zero for a hydrogen saturated compound. However,

the aromatic fraction begins at DBE 6 and extends past the saturate

fraction to DBE 28. Importantly, the analysis of the combined saturate

and aromatic (equal weight/concentration) fractions yields a broad

distribution that encompasses both the individual saturate and aromatic

DBE distributions.

Figure 6.7 is the iso-abundant contoured image for the saturate,

aromatic and combined saturate and aromatic fractions S1 class. The

same trend established in the DBE distribution graph (Figure 6.6) is now

represented in DBE image format. The lower DBE species are found in

the saturate fraction, higher DBE species in the aromatic fraction, and a

combination of the individual fraction DBE values in the combined

fraction image. Thus, it appears from Figures 6.6 and 6.7 that APPI

ionizes a wide range of DBE values with comparable efficiency. This

suggests that the abnormally high abundance of the low DBE S1 species

observed in the methylated VBR ESI analysis and whose presence in the

VBR is confirmed in the APPI mass spectral analysis of the SARA

fractions, is a result of the enhanced methylation reactivity toward low

88

1.5

10.5

20

.5

15

.5

5.5 28

25

.5

Vacuum Bottom Residuum

APPI DBE Distribution

S1 Class

Saturates

Aromatics

Saturates+

Aromatics

Double Bond Equivalents

Figure 6.6. S1 DBE distribution of the saturates, aromatics, and the saturate/aromatics solutions. The calculated DBE values (equation 1.19) are for the cation (not the neutral species). Therefore, non-integer values are possible for protonated compounds [M + H]+. The analysis of the combined saturates and aromatics (equal weight/concentration) show a broad distribution which encompasses both the individual saturate and aromatic DBE distributions.

89

Figure 6.7. Iso-abundant contoured image for the S1 class of the saturates, aromatics and saturates/aromatics solutions. Relative ion abundance within the class is color scaled in the z-axis. The same trend seen in the DBE distribution graph (Figure 6.7) is represented in the images. The lower DBE species are found in the saturate fraction, higher DBE species in the aromatic fraction, and a combination of the individual DBE distribution values in the combined image.

90

DBE S1 species and not due to DBE specific APPI ionization efficiencies.

Therefore, the low DBE S1 species in the saturate fraction (Figure 6.6

and 6.7) must have a low abundance (a reasonable assumption because

this is a vacuum bottom residue) and these low abundance, low DBE S1

species are not observed because they are simply below the detection

limit. These results suggest that although chemical derivatization

methods allow for nonpolar sulfur speciation by ESI, it does not

efficiently methylate high DBE sulfur species. Thus, the chemical

derivatization method presented here does not provide accurate sulfur

speciation for petroleum materials that contain high DBE (>10) sulfur

species and is therefore inherently limited to light distillate fractions.

Conclusions

In this report, we speciate the S1 class of a vacuum bottom residue

with two ionization methods coupled to a 9.4 Tesla FT-ICR mass

spectrometer. The ionization methods demonstrated remarkably

different S1 DBE distributions. The ESI analysis for the methylated raw

VBR showed an S1 class with a distribution maximum centered at 7-10

DBE. The APPI analysis for the raw (not methylated) VBR showed an S1

class with a distribution maximum centered at 24-28 DBE.

The APPI analysis of the saturate, aromatic and combined saturate

and aromatic fractions showed equal ionization efficiency over a broad

DBE distribution. This leads us to conclude that APPI does not

discriminate against lower DBE species at similar molar concentration.

Also, the APPI S1 DBE distribution for the VBR (methylated and

not methylated, Figures 6.2 and 6.4) differ in the low DBE range, i.e., the

methylated APPI S1 image (Figure 6.4) is lacking the low DBE species

seen in the unmethylated sample (Figure 6.2). We postulate that the

methylation of the lower DBE S1 species render them unobservable by

91

APPI. Furthermore, we conclude the methylation reaction is sterically

hindered for large DBE species (> 10 DBE). Not only because larger DBE

species (> 10 DBE) were detected with an APPI source but also because

this sample is a vacuum bottom residue which form our experience

should contain high DBE species.

Future research will further investigate the steric hindrance for the

methylation reaction and comparison analysis of other high sulfur

petroleums.

92

CHAPTER 7. CONCLUSIONS AND APPI FT-ICR MS APPLICATION AND COLLABORATION WITH THE INSTITUTE OF PETROLEUM AT

FRANCE; A REAL WORLD APPLICATION

Assessment of APPI Technology

The application of APPI coupled to FT-ICR mass spectrometry can

provide elemental composition of complex mixtures. Chapter 2

demonstrated the unmatched resolving power and mass accuracy of

FT-ICR mass spectrometry. The dual ionization pathways of APPI can

complicate mass spectra. Formation of even and odd electron cations

translates to closely spaced mass spectral doublets that must be resolved

for meaningful elemental assignments. For example, the difference

between [C23H1413C]+� and [C24H14+ H]+ is 4.5 mDa (13C vs. CH), and a 1.1

mDa mass doublet corresponds to the mass difference between C4 and

SH313C, e.g., from the protonated molecule [C24H29N1S1

13C1 + H]+ and the

radical molecular ion [C28H27N1]+� (Figures 2.3 and 2.4). Deuterated

solvent experiments present their own unique mass doublets.

Nevertheless, FT-ICR MS can also resolve these mass doublets, e.g., the

1.5 mDa mass split which results from compounds that differ in

elemental composition by H2 and D (Figure 4.7).

Conveniently, toluene is a good solvent for petroleum and an

excellent dopant for APPI. However, toluene radical cation formation and

solution vaporization temperature causes concern. One approach to

validate new experimental techniques is through comparative studies. In

Chapter 3, analyte fragmentation was addressed with model compounds

and ESI comparison studies. Fortunately, petroleum analysis by ESI

FT-ICR mass spectrometry is a well established soft ionization method in

this laboratory. Therefore, comparison of ESI spectra with APPI spectra

provided a foundation to build upon. The results from Chapter 3

93

identified fragmentation sources and established instrument parameters

to avoid fragmentation. Confidence was gained through model

compound spectra and APPI versus ESI petroleum analysis comparison.

Spectra presented in Chapter 3 shows that proton transfer

reactions are the dominant ionization pathway for pyridinic and pyrrolic

nitrogen compounds. Likewise, the nitrogen class compounds in a

petroleum sample preferentially form ions through proton transfer

reactions. Chapter 4 investigated the source of the proton for APPI

generated ions. For high nitrogen content petroleum, e.g., Canadian

Athabasca bitumen, a majority of the nitrogen classes formed positive

ions through proton transfer. To model the proton transfer, nitrogen

compounds with acidic and basic moieties were analyzed in toluene and

deuterated toluene. It was determined that a majority of the proton

(deuteron) charge arises from reactions with other species present in the

solution matrix even though toluene (or deuterated toluene) is present in

much greater molar concentration. This was true for the petroleum

sample also. Interestingly, also presented in this chapter, APPI sources

produce a cloud of positive and negative ions simultaneously.

Chapter 5 presented the thrust for APPI application, i.e., speciation

of sulfur and other non-polar species in petroleum. As a first step, a

crude oil was analyzed without any sample preparation to demonstrate

the power of the technique. Furthermore, the crude oil was separated by

a common petrochemical fractionation method and each fraction was

individually analyzed. This chapter established the first detailed sulfur

speciation a crude oil and its elemental composition yielded the most

aromatic sulfur species ever detected by mass spectrometry.

Chapter 6 investigated sulfur speciation by APPI FT-ICR MS and

comparatively, ESI FT-ICR MS of a chemically derivatized petroleum

sample. The ionization methods demonstrated remarkable differences

for the sulfur containing compounds, i.e., different S1 DBE distributions.

The derivatized ESI sample spectrum was limited to lower DBE sulfur

94

species relative to the APPI sulfur species. It seems that the chemical

derivatization is hindered for larger DBE species. Overall, evidence is

provided that suggest APPI is a more generalized (equal ionization

efficiency) ionization technique and may provide equal ionization

efficiency across a broad DBE and polarity of compounds.

APPI FT-ICR MS Applied to Current Petrochemical Challenges

Chapters 2 through 6 developed and established a new analytical

ionization technique for the elemental speciation of petroleum.

Throughout the chapters, the need to characterize the sulfur containing

species in petroleum to enhance refinery technology was emphasized.

The ultimate utility of APPI FT-ICR mass spectrometry applied to

petrochemical analysis will be found in monitoring molecular changes

before, during and after refinery processes. In the following sections, I

present data collected in collaboration with the Institute of Petroleum at

France (IFP). A real world application for APPI FT-ICR mass

spectrometry; Stepwise Molecular Characterization of an Asphaltene

Hydroconversion Process.

Introduction

The following introduction was provided by Isabella I. Merdrignac, an IFP

research scientist.

While residue fuel oil demand has drastically decreased over the

last decade, the demand for motor fuel derived from light and middle

distillates is still increasing. However, light conventional crude oil

production is declining and is being replaced by heavier,

non-conventional crude oils. The main characteristics of heavy crudes

(high viscosity and high heteroatom content) are directly related to the

significant abundance of compounds such as resins and asphaltenes.

95

Concentrated in residue, they constitute the most polar fractions of these

products.79 To enhance the valorization of such oils, various upgrading

processes have been developed.80, 81 Hydroconversion processes

(Hyvahl82 and H-Oil) require catalysts to remove and accumulate metals

(nickel and vanadium) and to desulfurize the feed.

Although our knowledge has considerably improved in the last two

decades, some industrial processes are not fully understood. In the

refining process, we know that feedstocks with very similar composition

convert in different ways or can induce variable aging of catalysts. The

compositional analysis of heavy oil products has become a key step in

various developments. However, the characterisation of such species

still remains time consuming despite substantial efforts in this field.

The complexity of these oil matrices tends to increase with their

boiling point. A large variety of compounds which vary in structure and

molecular weight are present. Asphaltenes are defined by their

insolubility in a normal paraffinic solvent. They consist of a

heterogeneous mixture of highly polydispersed molecules either in terms

of size or chemical composition, with a high content of heteroatoms and

metals. In solution, they exhibit self-assembly and colloidal behaviour,

depending on the operating conditions.83 Dissolved in residue, they may

precipitate easily during hydroconversion due to chemical composition

changes of the residue. Asphaltenes are known to be coke precursors

and catalyst inhibitors. The deactivation of catalysts is thus strongly

dependant on the heavy fractions concentration. Numerous analytical

techniques regarding asphaltenes characterization have been

performed.84 Among them, APPI FT-ICR mass spectrometry can provide

elemental molecular speciation and is the focus of our collaboration.

96

Residue Sample Overview

The IFP selected a crude oil residue for analysis and performed a

standard SARA method fractionation. As previously stated, asphaltenes

are the most complex fraction in a crude oil and, even more so,

asphaltenes precipitated from a vacuum bottom residue. Crude oil

residue is the portion of petroleum which remains after successive

distillation steps to remove lighter fractions under vacuum. Therefore,

the asphaltene fraction of a vacuum bottom residue are heteroatom rich

highly condensed polycyclic aromatic compounds.

The asphaltene fraction was subjected to hydroconversion in a

bench-top unit representative of industrial conditions.85 A general

scheme of the asphaltene conversion process and samples analyzed is

depicted in Figure 7.1

Figure 7.1. Residue hydroconversion scheme. Sample designations A1, A2, A11 and A22 reflect hydroconversion in fixed bed conditions. Sample A1 and A2 were reacted at different temperature (hydrodemetalization) and further reacted to produce A11 and A22 (hydrodesulfurization). Samples B1, B2, and B3 were obtained in ebullated bed conditions at different increasing residence times.

97

All samples (to include the saturates, aromatics and resins) were diluted

to the same concentration (1 mg/mL) and analyzed by APPI FT-ICR mass

spectrometry in negative and positive ion mode.

Table 7.1 is a compilation of all samples analyzed (negative and

positive ion). The elemental peak assignment values represent all

spectral peaks that could be assigned a unique molecular formula based

on mass accuracy and homologues series. Although the negative ion

spectra were acquired, initial data reduction presented here will focus on

positive ion data.

Table 7.1. Total Elemental Peak Assignment and Root-Mean-Square Mass Error (mass error, difference between experimentally measured mass and the exact mass corresponding to the elemental composition assigned to that mass spectral peak). The asphaltene alpha-numeric designators correspond to Figure 7.1.

Elemental Assignments Elemental Assignments Sample Positive ion (RMS error)* Negative ion (RMS error)* Saturates 3526 (228) 3021 (103) Aromatics 5675 (176) 11913 (257) Resins 2783 (145) 8305 (323) Asphaltenes Feed 5624 (423) 3268 (282) A1 5905 (432) 4939 (319) A11 2881 (232) 5812 (450) A2 4040 (303) 6792 (410) A22 2971 (296) 4589 (441) B1 4608 (452) 5466 (470) B2 3564 (278) 4128 (384) B3 1823 (262) 2997 (434) * error reported in parts per billion (ppb)

The total unique elemental formulas assigned for the complete

sample set (all samples in Table 7.1) was 104,630. This includes isotopic

variants and elemental species overlap between samples. Noteworthy,

the rms mass error for all samples is < 500 ppb (parts per billion).

98

m/z

700650600550500450400350300

479478477476475

m/z

478.10478.08478.06478.04m/z

476.10476.04

[C30H18S3 + H]+

[C29H18S313C1 + H]+

[C29H18S213C1

34S1 + H]+

IFP

Aromatic FractionAPPI FT-ICR MS

476.07

Figure 7.2. Broadband APPI FT-ICR mass spectrum of the IFP aromatic sample (bottom). Zoom insets (top) identify [C30H18S3 + H]+ (64 % relative abundance), [C29H18S313C1 + H]+ (22 % relative abundance, and [C29H18S213C134S1 +H]+ (3 % relative abundance).

99

Figure 7.2 is the broadband positive ion APPI FT-ICR mass

spectrum (bottom) of the aromatics. The zoom insets (top) identify an S3

class compound and one of its isotopic variants. High sulfur content raw

crude oils (not vacuum bottom residue) typically have S1 and S2 class

species at relatively high abundance and S3 species at lower abundance.

For this sample, the multiple heteroatom species are concentrated, and

the S3 species is present at high spectral relative abundance. Hence, the

[C29H18S213C1

34S1 + H]+ isotope of the [C29H18S313C1 + H]+ isotope is

detected (which has never before been detected for a petroleum sample).

Asphaltene Analysis

Positive ion APPI FT-ICR mass spectra for each sample was

acquired and spectral peak assignments were sorted by heteroatom

class. The feed asphaltene analysis revealed a heteroatom-rich class

distribution. Figure 7.3 is the relative abundance of the classes detected

for the positive ion spectrum. For the greater abundant classes (> 1 %

relative abundance, Figure 7.3 top), fifteen of the seventeen classes

contained one or more sulfur atoms. Not surprising, the hydrocarbon

class was detected in low abundance.

Samples A1 and A2 represent the catalyzed reaction products at

two different temperatures. The class analysis (Figure 7.4) reveal a

reaction threshold was crossed between the temperatures (380 °C and

400 °C). For sample A-1, a high percent of sulfur containing compounds

are still present; although, the hydrocarbon (HC) relative abundance has

increased in comparison to the feed asphaltene (Figure 7.3). Sample A-2

shows a large relative reduction in the sulfur classes which is

accompanied by an increase in the HC class. Relative abundance of Sx

species in the partial-conversion A1 sample are similar to those of Sx+1 in

100

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

S2 S3 S1 N1S2

S4 N1S1

N1S3

O1S2

N1O1S1

HC N1O1S2

N1 O1S3

O1S1

N1O2

S5 N2S1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

N1O1

N2O1S1

N1O1S3

N2S2

N2O1

N2 N3S1

N1S4

O1 N4 O1S4

N2O1S2

N4S1

N3S2

O2S2

O2S1

N1O2S1

O3 N4O1

O4 N1O2S2

O4S1

O4S2

APPI FT-ICR MS

Asphaltene Feed

Heteroatom Class Distribution

Class Distribution Continued

Class

Su

m R

ela

tive

Ab

un

da

nc

e

Figure 7.3. Heteroatom class distribution for the IFP asphaltene sample. Forty

heteroatom classes were assigned. For classes above 1 % relative abundance (top), 15 of the 17 classes contain one or more sulfur atoms. Also note the hydrocarbon class (HC) is present in low abundance.

101

S1 S2 HC N1

S1

N1 S3 N1

S2

N2 O1

S1

O1 N1

O1

N2

S1

O1

S2

N1

O1

S1

S4

A1

A2

Heteroatom Class Distribution Comparison

A1 (380 °C) versus A2 (400 °C)

Class

Re

lati

ve

Ab

un

da

nc

e

Figure 7.4. Class distribution for samples A1 and A2 (Figure 7.1). Each sample is normalized to the most abundant class within its class distribution, i.e., they are mutually exclusive. Sample A1 was reacted at 380 °C and sample A2 at 400 °C.

102

the feed and therefore suggest a reaction pathway like Sx A1 = Sx feed +

Sx+1 feed.

Figure 7.5 is a three dimensional iso-abundance DBE versus

carbon number plot of the sulfur classes of the feed compared to the A1

sulfur classes (and HC). This type of plot represents all the detected

species for a given class displayed in one visual image. However, each

plot is normalized to the highest spectral magnitude ion within that plot.

Hence, relative abundances between classes are represented in bar

graphs (Figure 7.4), and relative ion abundance within a class is depicted

in iso-abundance contoured plots (Figure 7.5 and 7.6).

The relative abundance of the sulfur species remained high for the

A1 sample. The S3 species in the feed would, presumably, be detected as

S2 species in the A1 sample and so forth. However, the A1 S2 species

exhibit a higher DBE (3-4 DBE) than the feed S3 species and also an

increase in carbon number (~6 carbons). Likely, there are condensation

reactions occurring (forming rings and double bonds) and, the A1 S2

species also include unreacted feed S2 species because there is only a

small percent of the sulfur species converted at this reaction

temperature. In any case, there should have been a rearrangement of

the sulfur families since the sulfur content decreased from 8 wt% in the

feed to 7.2 wt% which is not much compared to the asphaltene

conversion (47 %).

Figure 7.6 is the comparison of the feed asphaltene to the A2

sample (reacted at higher temperature). At higher temperature, the A-2

sample showed a larger reduction of the sulfur species (Figure 7.4) which

corresponds to elemental analysis (8, 7.2 and 3.5 wt% sulfur in the feed,

A1 and A2, respectively). However, comparison of Figures 7.5 and 7.6

show little, if any, difference between A1 and A2 sulfur and hydrocarbon

species. Hence, higher reaction temperature increased the rate at which

sulfur is removed but produced similar hydrocarbon species.

103

Figure 7.5. Iso-abundant contoured DBE versus carbon number plot of the feed asphaltene and A1 sample; sulfur and hydrocarbon classes. Relative ion abundance is color scaled in the z-axis. A dashed reference line is added to enhance graph-to-graph comparison.

Figure 7.6. Iso-abundant contoured DBE versus carbon number plot of the feed asphaltene and

A2 sample; sulfur and hydrocarbon classes. Relative ion abundance is color scaled in the z-axis. A dashed reference line is added to enhance graph-to-graph comparison.

104

The heteroatom abundance of the final reaction products (A11 and

A22) for this reaction branch (A1→ A11 and A2 → A22) is represented in

Figure 7.7. Sample A1 and A2 reaction vessels utilized a macroporous

(micrometer pore size) catalyst at different temperatures. These samples

(A1 and A2) were the feedstock for further sulfur reduction which

produced samples A11 and A22 (reacted with a mesoporous catalyst

(angstrom pore size)). The final class composition of A11 and A22 are

nominally identical in species and relative abundance. However,

elemental analysis exhibited differences. Sulfur content for A11

decreased from 7.2 wt% (A1) to 4.5 wt% (A11), and for A22 from 3.5 wt%

(A2) to 1.6 wt% (A22).

HC N1 O1 N1 O1 S1 O2

Class

Re

lati

ve

Ab

un

da

nc

e

A11

A22

Heteroatom Class Distribution Comparison

Figure 7.7. Heteroatom class distribution of the final reaction products (A11 and A22).

Figure 7.8 is a comparison of the hydrocarbon species from A11

and A22. The graph highlights differences in aromaticity (defined as the

carbon number to DBE ratio). For A11, the highest abundant species

are centered at ~45 carbon and 27 DBE. Sample A22 shows a distinct

shift toward the line of demarcation which corresponds to an increase in

aromaticity. The line of demarcation is a carbon number to DBE ratio

105

Figure 7.8. Iso-abundant contoured DBE versus Carbon number plot for the hydrocarbon classes of A11 and A22. A22 shows an increase in aromaticity (increase in carbon number-to-DBE ratio).

106

boundary between planar carbon structure and bowl shaped structure,

e.g., coronene versus corranulene.

The second hydroconversion reaction branch (feed → B1, B2, B3)

was carried out under similar catalytic conditions as A2 with increased

temperature (427 °C) and increasing conversion time. Elemental sulfur

analysis showed a decreasing weight percent, 5.5, 2.45 and 1.38 wt%

sulfur for B1, B2 and B3, respectively.

Figure 7.9 is the class distribution for samples B1, B2, and B3.

The increased temperature (B1 427 °C versus A2 400 °C) shows no

significant increase in the reduction of sulfur species, i.e., the HC, N1, S1,

and S2 relative abundances are comparable between A2 Figure 7.4 and

B1 Figure 7.9. As expected, increased catalytic reaction time results in

further reduction of sulfur accompanied by an increase in hydrocarbon.

HC N1 S1 O1 S2 N2 N1

O1

N1

S1

O1

S1

S3

B1

B2

B3

Increasing

Time

Rela

tive

Ab

un

da

nce

Class

Class Distribution Comparison B1, B2 and B3

Figure 7.9. Class distribution for samples B1, B2 and B3. With increasing hydroconversion time, there is a corresponding reduction in sulfur species with an increase in hydrocarbon species.

Finally, Figure 7.10 is a comparison of the hydrocarbon classes for

samples B1, B2, and B3. The plots in Figure 7.10 display a progression

107

C36H16 C38H16 C40H16

a cb

Figure 7.10. Iso-abundant carbon number versus DBE contoured plots for the hydrocarbon classes of samples B1, B2 and B3. The plots display an overall migration of the most abundant species toward greater aromaticity. Structures a, b, and c (bottom) represent the predicted stable structures which correspond to elemental species hot spots for sample B3.

108

to more aromatic structures with increased catalytic residence time. The

proposed compounds (Figure 7.10 bottom) represent stable aromatic

structures that correspond to high ion magnitude in the spectrum. The

structures are only one possible isomer. However, a polycyclic aromatic

hydrocarbon with a given number of aromatic sextets (highlighted red) is

more stable than an isomer with fewer.86 Figure 7.10 structures are the

isomers which allow the highest number of sextets.

Overall Conclusion

I have presented a stepwise analysis of a hydrotreated asphaltene

by APPI FT-ICR mass spectrometry. The hydroprocessing analysis

revealed no hydrocracking (carbon rejection) and an increase in DBE

associated with sulfur reduction. Temperature changes demonstrated

significant differences in sulfur reduction, and longer catalytic reaction

time exhibited structural migration to stable condensed polycyclic

aromatic compounds. One unanswered question remains surrounding

sample A11’s elemental analysis which showed a 4.5 wt% sulfur content

and yet the mass spectrum analysis was similar (low sulfur species) to

A22 (1.6 wt% sulfur): Are the sulfur species in sample A22 unobservable

by APPI? The answer to this question will require further experiments.

APPI FT-ICR mass spectrometry will be a useful tool for petrochemical

analysis!

109

APPENDIX A. CARBON CLUSTER STRUCTURAL CHARACTERIZATION BY GAS PHASE ION-MOLECULE REACTION IN

AN FT-ICR MASS SPECTROMETER

Fullerene Introduction

Fullerenes are closed cage molecules consisting of 12 pentagonal

and two or more hexagonal rings. Fullerenes with 60 carbon atoms or

larger follow the isolated pentagon rule (IPR).87 Smaller fullerenes

consist of isomers with adjoined pentagon rings, e.g., fullerene C50.

Perhaps one of the more interesting small fullerenes is C28. The most

stable theoretical structure in part consists of four reactive carbons

bonded in sp3 orbitals located at the apex of triplet pentagons.88 It has

been suggested that fullerene C28 could form a crystal lattice

(hyperdiamond) because the four dangling bonds are centered at

tetrahedral vertices.89 Breda et al., suggest C28 fullerene could possibly

be a room temperature organic superconductor.90 Guo et al. has

provided experimental evidence that the tetravalent C28 fullerene is

stabilized with endohedral metals (U@C28).91

Laser vaporization of graphite followed by supersonic expansion is

known to produce stable (magic number) fullerenes, e.g., truncated

icosahedral C60.92 Lower mass Cn clusters (10 ≤ n ≤ 18) are reported to

consist of linear chain and monocyclic ring structures, and higher mass

clusters (32 ≤ n ≤ 60) are the beginning of fullerene structures.93 Cluster

mass distribution is source condition dependent. A bimodal distribution

(Cn (10 ≤ n ≤ 18) and (32 ≤ n ≤ 60)) or single distribution inclusive of Cn

(19 ≤ n ≤ 31) is possible. Small carbon clusters between the bimodal

distribution (C28) are the focus of this report.

110

Instrumentation

Cluster Source

An FT-ICR mass spectrometer with a split-pair 5.3 Tesla

superconducting magnet94 and associated ion optics and electronic

equipment was purchased from Lucent Technologies, New Jersey. Figure

A.1 is a sketch of the complete instrument configuration at Lucent

Technologies.

5.3 Tesla

Cryo pump Cryo pump

Diff Pumps

X2 X2

Diff Pumps

Source

Conflated Bore

10-4

10-6

51.75

5

100

30

50 24 49 35

158

50 40

73

10” flange

Figure A.1. Diagram of the 5.3 Split-pair FT-ICR mass spectrometer (unshielded magnet) in its original configuration at Lucent Technologies (not to scale). The eight inch bore of the magnet is vacuum sealed and was designed with four access ports which allows trapped ion interrogation within the ICR cell.

The instrument included an external cluster ion source. The cluster ion

source produces laser ablated clusters in the presence of a continuous

helium gas stream. The carbon clusters experience supersonic

111

expansion into an optics lens stack constructed with a mechanical 10°

offset from the z-axis (bore axis of the magnet). Figure A.2 is a diagram

of the optics.

Source

Potential

(5-50 V)

Extraction

Potential

(-100 to -900 V)

X – Y Deflection Potentials

Center Einzel Lens

Common

Figure A.2. Ion optics lens stack. This lens stack is mounted to the source block. The first electrode (labeled source potential) is physically connected to the source block and, therefore at the same potential as the source. Note the mechanical 10° offset of the final two electrodes.

The first electrode is electrically connected to the source block and the

conical shape protrusion comprises the exit wall (when mounted to the

source block) of the cluster formation chamber. The source electrode

orifice is 1 mm in diameter, and other electrodes with larger orifices were

manufactured (1.5 mm and 2 mm diameter) but not installed. All

electrodes are mutually insulated. Nominal electrode potentials are as

follows: source, +20 V; extraction lens, -110 V; center Einzel lens, -150

V; all other electrodes are held at ground potential. The mechanical 10°

offset prevents a pathway for the cluster neutral beam to the ICR cell.

The instrument was not configured with neutral beam ionization

capability.

112

10-6 Torr 10-7 Torr 10-7 Torr 10-9 Torr 10-10 Torr

ICR Cell

Cell Pulse Gas

Transfer Octopole

Accumulator Octopole

Conductance Limits 1, 2, and 3

Laser Port

Carbon Rod

Gas Valves Einzel Lens

Carbon Laser Vaporization

FT-ICR MS

Cluster Source Existing 9.4 Tesla FT-ICR MS

2

1

Figure A.3. Ion optics and differential pumping diagram. The zoom inset details the source block and static potential optics. Conductance limits 2 and 3 are held at trapping potentials during external ion accumulation.

113

Cluster Source Coupled to Existing 9.4 T FT-ICR Mass Spectrometer

Figure A.3 is a diagram of the cluster source chamber coupled to

the existing 9.4 Tesla FT-ICR mass spectrometer.40 The original cluster

source chamber was configured with three Edwards 250M diffusion

pumps (ion source chamber) and a Varian (model unknown) diffusion

pump for the second source chamber. Two source chamber ports were

sealed with iso-250 blank flanges. The third source port and second

chamber port were adapted for Pfeiffer Balzer turbo molecular vacuum

pumps. When not in operation (no helium gas flow) and under vacuum,

the mass spectrometer’s pressure is indicated in Figure A.3.

Figure A.4. Interface octopole ion guide. The octopole operated at 1.4 - 2.6 MHz and ~300 volts peak-peak amplitude with a -30 V DC offset. The overall length was ~27 inches.

114

Figure A.4 is a diagram of the interface ion optics that coupled the

cluster chamber to the mass spectrometer. The cluster source lens stack

was positioned .030 inches from conductance limit 1 (CL1) orifice. The

octopole shell is supported in two locations. The first support allows

z-axis translation and x-y plane alignment and a set screw for a ridged

mount near CL1. The second support, is a slip fit mount that allows z-

axis translation and adjustment in the x-y plane without a set screw.

The end of the octopole (opposite CL1) was positioned .050 inches from

CL2. Interestingly, after installation of the interface octopole (A.4), the

system was evacuated for the first time. The outer wall of the source

chamber (surface facing the mass spectrometer) is constructed of 3/4

inch stainless steel. With the system under vacuum, the interface

octopole rods contacted CL2. The 3/4 inch thick steel wall had deformed

at least .050 inch and, therefore, translated the octopole toward CL2.

The octopole was positioned an additional .030 inches (total .080 inch)

from CL2 to compensate.

The source target (carbon) rod (1/4 inch diameter, 5 inch length) is

simultaneously rotated and translated. The original drive motor failed.

A replacement motor was purchased from MicroMo Inc. (part number,

1516E012ST+15/8 1670:1+X0583). The motor rotates the rod at

~300 mHz and a translation distance of one inch. Micro limit switches

positioned on the source reverse the motor direction, and thus, the motor

drive system provides continuous rotation and translation of the target

rod.

An Nd:YAG laser (2nd harmonic) produces 25 mJ pulses (1-15 Hz)

to ablate the rod. The laser head is rigidly mounted, and an array of

mirrors and a 500 mm focal length lens focused the laser on the target

rod. Without rod rotation, the laser was fired multiple times to ablate a

hole into the rod. The diameter of the hole was .035 inches.

115

Extraction -110 V, Source +30 V

0

100

200

300

400

500

600

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125

CL2 potential, Volt

Pic

oam

pe

re

CL1 - 160 V

CL1 - 110 V

CL1 - 60 V

Retarding Potential

Extraction -110 V, CL1 -161 V

0

100

200

300

400

500

600

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 110 120 130 140 150

CL2 potential, Volt

Pic

oa

mp

ere

Source Potential +40 V




CL1 -160 V, Source +30 V

0

100

200

300

400

500

600

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 110 120 130 140 150

CL2 potential, Volt

Pic

oam

pere

Extraction Potential -50 V



Figure A.5. Retarding potential profile. Total ion current (y-axis) is measured on accumulator octopole rods and CL2 potential (x-axis) is varied. CL2 is the accumulator entrance lens. Source, extraction, and CL1 potentials are plotted to investigate ion kinetic energy.

116

Retarding Potential Study

The laser optics were adjusted to maximum ion current measured

on the common lens (see Figure A.2, common). With continuous laser

shots (10 Hz) and a continuous stream of helium into the source block,

the maximum obtainable current (on the common electrodes) was 1.5

nano-amperes (measure with a Keithley pico-ampere meter). For this

measurement, the extraction lens was held at -110 volts, and the helium

gas leak rate was increased until the pressure in the source chamber

was 1 x 10-4 Torr.

For the retarding potential study, the pico-ampere meter was

connected to the accumulator octopole rods. Source, extraction and CL1

potentials were varied sequentially (two potentials held constant and one

varied) and pico-ampere (collected on the accumulator rods) versus CL2

potential were recorded.

The source potential has the greatest affect for ion current

collected on the accumulator octopole rods (Figure A.4 (top)). The source

potential sets the initial ion kinetic energy. The extraction and CL1

potential have minimal (if any, Figure A.4 middle and bottom)) affect on

accumulator ion current. However, the accumulator ion current is the

total ion current composed of a broad cluster mass range.

Experimentally, to optimize instrument parameters for a desired mass

range, a source potential of 30-40 volts was not always optimal. The

average kinetic energy of the ion clusters is ~60 eV.

Cluster Spectra

Mass Range

117

The detected mass distribution can be altered by rf-octopole

parameters and ICR cell trap plate timing. Preferred m/z ion abundance

m/z1,2001,1201,040960880800720640560480400320

Carbon Laser Ablation FT-ICR MS

Jeremiah Purcell

Don Smith

John Quinn

Carbon Target Rod

10 Acquisitions summed

200 Laser Pulses/Acquisition

Continuous Helium Stream

C60C50

Figure A.6. Carbon cluster broadband FT-ICR mass spectrum. Spectra was collected on the initial day of instrument operation. Additional instrument parameter are reported in Table A.1.

Table A.1. Spectra Instrument Parameters

Fig. A.5 Fig. A.6 Fig. A.7 Source, Volt 5 20 20 Extraction, Volt -100 -110 -110 Einzel Lensa, Volt -100 -150 -150 CL1, Volt -60 -40 -45 RF Oct 1, MHz 2.0 (1 V) 1.4 (1 V) 2.2 (1 V) RF Oct 2, MHz 2.0 (1 V) 1.4 (1 V) 3.2 (1.6 V) RF Oct 3, MHz 2.0 (1 V) 1.4 (1 V) 2.2 (1 V)

a Center Einzel lens

118

m/z4,6004,4004,2004,0003,8003,6003,4003,2003,0002,8002,600

m/z3,3463,3443,3423,3403,3383,3363,334

12C278+�

12C27513C3

+�

Single Acquisition

5 Laser Pulses


Figure A.7. Broadband carbon cluster mass spectrum (2600 ≤ m/z ≤ 4600). Instrument parameters favored accumulation and transfer of high m/z ions. The zoom inset shows the C278 monoisotopic peak and its isotopic variants.

can be increased with longer accumulation times and instrument

parameter adjustments.

Figure A.6 is a representative spectrum acquired on the first day of

operating the instrument. Spectral peaks at m/z 600 (C50) and m/z 720

(C60) are enhanced. Other instrument parameters for Figure A.6 (and

other spectra figures) are reported in Table A.1.

Figure A.7 is a high m/z broadband mass spectrum and was

acquired by adjusting instrument parameters to optimize accumulation

and transfer of high m/z ions. Note that Figure A.7 is a single

acquisition mass spectrum, and Figure A.6 is 10 acquisitions summed.

Both display similar signal-to-noise ratios. Furthermore, the spectrum

119

in Figure A.6 was acquired with an ion population from 200 laser pulses

and Figure A.7 from 5 laser pulses. With the instrument configured for

continuous helium sweep gas, the bulk of the ion population formed is

high m/z ions.

Nevertheless, with the instrument in a continuous gas stream

configuration, a significant low m/z ion population could be

preferentially accumulated. Figure A.8 is an example of the low m/z ion

population centered at m/z 336 (C28). Although the spectrum is a single

acquisition, it required 400 laser pulses.

m/z650600550500450400350300250200

C28+�

Single Acquisition

400 Laser Pulses


Figure A.8. Low mass carbon cluster mass spectrum. Although this is a single acquisition, 400 laser pulses were required to accumulate this ion population.

In-Cell Gas-Phase Ion-Molecule Reactions

In-cell ion-molecule reactions were accomplished by SWIFT (stored

waveform inverse Fourier transform) isolation followed by cell pulse gas

events. Lecture bottles of nitric oxide and chlorine were purchased from

Sigma Aldrich and fitted with a regulator. The output of the regulator

120

was connected to a gas bomb with Sulfurinert® 1/16 inch o.d. tubing.

The gas bomb (~5 Torr gas pressure) was connected to the ICR cell region

through a pulse valve (General Valve Co.).

Figure A.9 represents the in-cell gas phase reaction of C28 with

nitric oxide (NO). The addition of one NO adduct to C28 is seen at m/z

366. Other experiments with longer (and multiple) pulse gas duration

m/z

380370360350340330320310300

[C28]+�

[C28NO]+�m/z

314313312311310

[C26]+�

C28 SWIFT Isolated

30 msec Pulse NO gas

Figure A.9. SWIFT isolated C28 with a 30 msec NO pulse gas event. The [C28NO]+� spectral peak magnitude is 13% relative abundance. The loss of C2 ([C26]+�) spectral peak is 1 % relative abundance.

(20 ≤ msec ≤ 50) showed no increase in the relative abundance (RA) of

the [C28NO]+� species. Additionally, the mass spectral peak

corresponding to [C28H1(NO)2]+� at m/z 397 was detected at 1 % RA. The

source of the hydrogen impurities are unknown.

As stated earlier, the theoretical stable structure of fullerene C28

contains four carbons atoms at the vertices of triple pentagon structures

(Figure A.10). The reaction of fullerene C28 at the four reactive carbon

121

sites (Figure A.10) should be exothermic.88 Furthermore, the

experimental conditions for Figure A.9 were such that the pulse gas

event resulted in a momentary spike in the pressure to ~1 x 10-6 Torr

(from 2 x 10-10 Torr). At this pressure, the C28 clusters undergo hundreds

of collisions with NO molecules. However, in Figure A.9 the predominate

reaction product is the addition of only one

Figure A.10. Theoretical stable structure of fullerene C28. The four red carbon atoms are at the vertices of triplet pentagons. In this isomer form, the red atoms have sp3 orbitals with a lone electron.

adduct (NO) and not multiple additions of NO. Furthermore, a large

percent of the parent ion ([C28]+�) remains unreacted.

Figure A.11 A (top) is the spectrum of a double resonance SWIFT

isolation experiment. C28 was SWIFT isolated in the ICR cell, reacted with

NO gas (30 msec pulse at 5 Torr), followed by another SWIFT isolation of

C28 and another pulse gas event. The reaction products of the first pulse

gas event are ejected from the ICR cell by the second SWIFT isolation

event. The second pulse gas event should produce more product

[C28NO]+� if more reactive species are present. However, only a small

122

m/z

380370360350340330320310300

m/z

380370360350340330320310300

[C28]+�

[C28]+�

SWIFT Isolation

Double Resonance

NO Pulse Gas

SWIFT Isolation

Without Pulse gas

m/z

368367366365364

[C28NO]+�

1 % RA

m/z

368367366365364

[C28NO]+�

2.5 % RA

a

b

Figure A.11. Double resonance SWIFT isolation of C28 with NO pulse gas. Experimental sequence spectrum A (top): SWIFT isolation C28, 30 msec NO pulse gas event, SWIFT isolation C28, 30 msec NO pulse gas event. Spectrum B (bottom) was recorded immediately (2 minutes) after spectrum A without NO pulse gas.

123

amount (2.5 % RA) of reaction product was detected after the second

pulse gas event in contrast to 13 % RA for the first pulse gas event

(Figure A.9). Even so, there is a small amount of reaction product in

Figure A.11(top). A few minutes after the experiment (depicted in Figure

A.11 top) was complete, the spectrum in Figure A.11 (bottom) was

acquired (no pulse gas). The relative abundance of [C28NO]+� had

decreased to 1 % RA. Subsequent experiments without a reaction gas

showed the species [C28NO]+� diminished to undetectable as the residual

reaction gas evacuated the ICR cell.

These results suggest the C28 cluster is present in the ICR cell in

two structural forms: one that reacts with NO and the other is non-

reactive (or a slower reaction rate constant). Bowers et al. performed

similar gas phase reactions for Cn (3 ≤ n ≤ 15) clusters.93 He noted fast

reacting rate constants for linear chain clusters (Cn, 3 ≤ n ≤ 10) and the

larger cyclic clusters (C11, C14, and C15) to be a factor of 10 slower.

Unfortunately, he reported no other cluster reactions for larger species.

Xie et al. reported isolation of fullerene C50 as C50Cl10.95 From Xie’s

work, it was concluded that one isomer of the C50 fullerene family has 10

reactive carbons. Figure A.12 is the mass spectrum of C50 reacted with

NO under the same conditions as cluster C28 (Figure A.8). Additional

reactions of other clusters with nitric oxide were also accomplished.

Table A.2 is a compilation of the reaction products (percent relative

abundance, RA). The relative abundance was normalized to the highest

spectral peak (the parent carbon cluster). In the addition column, the

((NO)2 + H) category is the mass spectral peak corresponding to 61

Dalton higher than the parent carbon cluster. The odd carbon clusters

reaction products did not contain this species (61 Da more than parent),

but did form species 60 Da higher in mass.

124

Table A.2. Percent Relative Abundance of Cluster Reaction Products

Addition, % RA Loss, % RA

(NO) (NO)2 ((NO)2 + H) C1 C2 C4 C6 C20 0.9 0.4 0.4 C22 4.1 0.8 C24 8.7 1.1 0.4 C26 15.7 1.3 0.8 C28 13.1 1.2 0.2 0.9 0.2 C29 6.8 3.3 C30 24.3 2.0 C31 25.7 10.3 C32 16.6 1.5 C34 11.2 1.3 1.1 C50 3.6 0.8 1.6 19.1 3.8 0.8

m/z640620600580560540520500

[C50]+�

[C44]+�

[C46]+�

[C48]+�

[C50NO]+�m/z534532530528526524

Figure A.12. Reaction of carbon cluster C50 with NO gas. The cluster (spectral peak at 600 m/z) was SWIFT isolated and reacted with a 30 msec NO gas pulse. The reaction product [C50NO]+� was detected at 3 % RA. The reaction also showed a strong loss of C2.

125

Additional pulse gas experiments were conducted with chlorine

gas. Two carbon clusters (C28 and C50) were SWIFT isolated and

subjected to a 30 msec pulse of chlorine gas before ICR excitation and

detection. The addition of one chlorine atom was detected for both

species, however, at low relative abundance (1-2 % RA).

Chlorine is a more polar compound than nitric oxide. The 30 msec

pulse of gas for chorine required an extensive (5-10 minutes) pump down

delay before ICR excitation and detection. Furthermore, after several

pulse gas events, the pressure in the ICR cell could not fully recover to

normal operating pressure (3 x 10-10 Torr). Therefore, excitation of ions

to detectable ICR radii resulted in more than desirable collisions and

possible loss of reaction products.

Conclusions

In the current configuration, the laser ablation of carbon in a

continuous helium steam produced a large m/z range ion population

(200 ≤ m/z ≤ 5000). The bulk of the ion population consist of higher

mass ions (> 1000 Da). In-cell gas phase reaction results (with nitric

oxide) indicate that the C28 carbon cluster is present in the form of at

least two chemical structures. Overall, instrument parameters do not

produce predominant spectral peaks for 720 Da and 840 Da (known

masses which correspond to stable fullerenes). Although, the spectrum

in Figure A-5 does show a larger relative abundance for C50 and C60.

Other reports92, 96 show enhanced formation of magic fullerene

masses (C28, C50, and C60). These experimental apparatus were

configured for a pulsed gas (helium) event (not continuous gas stream)

coincident with each laser shot. Additionally, the neutral cluster beam

was photoionized before mass detection. Hence, the current

configuration of this instrument differs substantially from earlier reports.

126

A helium pulse valve was installed at the source and tested (gas

valve 1, Figure A.3) at two mounting locations. The first valve was

installed approximately 1 meter from the target rod and external to the

source vacuum. Another experiment included a pulse valve mounted in

the source vacuum and approximately one-half meter distance from the

target rod. Both configuration allowed for diffusion of the gas pulse and

produced poor ion populations.

Further research will include modification of the source block to

mount a pulse valve within centimeters of the target rod (valve 2, Figure

A.3). Also, incorporation of General Valve Iota One pulse valve drivers

will enable a short pulse event (200-600 µsec) at high pressure.

Modifications will also include photoionization of the ablated neutral

beam.

127

APPENDIX B. REACTION OF HYDROGEN GAS WITH C60 AT ELEVATED PRESSURE AND TEMPERATURE: HYDROGENATION AND

CAGE FRAGMENTATION

The summary and introduction are presented in whole. The

results and discussion incorporate only the APPI FT-ICR MS analysis

accomplished at the NHMFL. Please refer to references 109 through111

for a full description.

Summary

Products of the reaction of C60 with H2 gas have been monitored by

high-resolution atmospheric pressure photoionization Fourier transform

ion cyclotron resonance mass spectrometry (APPI FT-ICR MS), X-ray

diffraction, and IR spectroscopy as a function of hydrogenation period.

Samples were synthesized at 673 K and 120 bar hydrogen pressure for

hydrogenation periods between 300 and 5000 min, resulting in the

formation of hydrofullerene mixtures with hydrogen content ranging from

1.6 to 5.3 wt %. Highly reduced C60Hx (x > 36-40) and products of their

fragmentation were identified in these samples by APPI FT-ICR MS. A

sharp change in structure was observed for samples with at least 5.0

wt % of hydrogen. Low-mass (300-500 Da) hydrogenation products not

observed by prior field desorption (FD) FT-ICR MS were detected by APPI

FT-ICR MS and their elemental compositions obtained for the first time.

Synthetic and analytical fragmentation pathways are discussed.

Introduction

Hydrofullerenes are products of C60 reaction with hydrogen.

Starting from the simplest hydrofullerene C60H2,97 many hydrofullerenes,

C60Hx, with various numbers of hydrogen atoms, 2 < x <44, have been

128

synthesized.98-102 Hydrogen reaction with C60 occurs by addition of H2 at

a C=C double bond, which results in formation of two C-H bonds.

Therefore, only an even number of hydrogen atoms is expected in neutral

C60Hx molecules. Of the several methods reported for synthesis of

hydrofullerenes, the most important are Birch reduction,98 reaction with

molten dihydroanthracene (transfer hydrogenation),99 and reduction by

zinc and hydrochloric acid.100 Typically, the two most abundant

hydrofullerene molecules from these reactions are C60H18 and C60H36

and, consequently, most hydrofullerene studies have been limited to

those products. Numerous characterization methods (X-ray diffraction

(XRD), NMR, IR, Raman spectroscopy, etc.)103-106 have been employed to

characterize those products. The high selectivity in synthesis of C60H36 is

explained by an inability of the above-mentioned synthesis methods to

reduce unconjugated double bonds (e.g., the minimum number of

hydrogen atoms required to leave unconjugated double bonds in each of

the pentagons of C60 is 36). Recently, it was discovered that

hydrofullerenes of the type C60Hx with x = 38-44 can be synthesized by a

Benkeser reduction (reduction by lithium in ethylenediamine).102 Highly

reduced C60 (with more than 44 hydrogen atoms attached) has never

been obtained in solid state. Until recently, there were relatively few

reports of C60 reacting directly with hydrogen gas. That reaction requires

elevated temperature (~573-673 K) and a hydrogen pressure of 50-120

bar and yields mixtures of hydrofullerenes with variable composition.107-

110 The resultant mixture is rather complex, and simple characterization

methods (such as IR spectroscopy and XRD) cannot speculate on the

reaction products. The maximum overall hydrogen content achieved after

prolonged hydrogenation (at 673 K and 100 bar H2) is ~5 wt %. Upon

prolonged hydrogenation, the sample weight initially increases due to

hydrogen addition and after reaching some maximum, starts to decrease

due to partial cage collapse.110 We recently showed that the final

products of C60 collapse are likely polycyclic aromatic hydrocarbons

129

(PAH).109, 110 Surprisingly, not only collapse but also fragmentation of the

cage structure was found under conditions of prolonged hydrogenation.

In our previous study, we reported synthesis of C59Hx and C58Hx as major

products after hydrogenation at elevated temperature/pressure: two

samples with relatively high degree of hydrogenation were analyzed by

high-resolution field desorption Fourier transform ion cyclotron

resonance mass spectrometry (FD FT-ICR MS).40 However, such analysis

destroys highly unstable hydrofullerene molecules (highly reduced C56-

60). Therefore, a complementary method is required for analysis of

“superhydrogenated” samples. Furthermore, FD FT-ICR MS was

performed only on highly reduced samples and the degree of

hydrogenation required for the onset of fragmentation (from C60Hx to C56-

59Hx) was unknown.111 Here we present a systematic analysis of samples

synthesized by reaction of C60 with H2 gas. By variation of the

hydrogenation period, samples with a broad range of hydrogen content

(1.4 - 5.3 wt %) could be synthesized. The complex hydrofullerene

mixtures were studied by IR spectroscopy, XRD and high-resolution

atmospheric pressure photoionization Fourier transform ion cyclotron

resonance mass spectrometry (APPI FTICR MS). The recently developed

APPI FT-ICR MS method66 has been employed for the first time for

analysis of hydrogenated fullerenes and shows promise as less

destructive than FD FT-ICR MS.

Experimental Section

High-resolution mass spectrometry was performed with 9.4 T

Fourier transform ion cyclotron resonance mass spectrometers equipped

with atmospheric pressure photoionization and field

desorption/ionization sources. Samples were dissolved in toluene and

either delivered at a flow rate of 100 µL/min into the APPI ion source or

deposited in 20-40 nL amounts on the filament emitter of the FD ion

130

source in vacuo. The nebulizing gas was supplied to the APPI ion source

at 80 psi and the nebulizer temperature was operated in the range of

200-350 °C. APPI produces both radical cations (loss of an electron) and

protonated cations. Radical ion formation in the APPI source results from

10 eV photons emitted by a krypton vacuum UV lamp or charge

exchange reactions with toluene cations, whereas protonated cations are

formed via proton-transfer reactions with toluene cations.19, 21, 23 The

generated ions were accumulated in an external (to the magnetic field)

octopole ion trap for 0.1-2 s prior to injection into an open cylindrical

Penning ion trap located in a homogeneous 9.4 T magnetic field. To

increase signal/noise ratio, transient time-domain ICR signals were

summed prior to fast Fourier transformation and magnitude calculation.

The experimental event sequence for the FD FT-ICR MS experiment has

previously been described in detail.111

Results and Discussion

APPI FT-ICR MS of Hydrogenated Samples

High-resolution APPI FT-ICR mass spectra were recorded from five

samples of C60 with different degrees of hydrogenation (Figure B.1) and a

non-hydrogenated reference C60 sample (data not shown). Note that

prior to analysis, the samples were dissolved in toluene and only

molecules soluble in that solvent will be detected. Due to the difference

in solubility for different hydrofullerenes as well as differences in

ionization efficiency, the relative ion abundances in the mass spectrum

may not correlate to the abundances of the corresponding neutral

synthesized hydrofullerenes. The ultrahigh resolution and ultrahigh

mass accuracy of FT-ICR MS allow for the unique elemental composition

assignment of each peak in a complex mass spectrum.

131

m/z 800750700

m/z 800750700

m/z 800750700

m/z 800750700

m/z 800750700

5.3 Wt%

3.4 Wt%

5.0 Wt%

3.8 Wt%

1.6 Wt%

Figure B.1. APPI FT-ICR mass spectra of C60 samples with different degrees of hydrogenation.

132

APPI FT-ICR mass spectra of pure C60 and low hydrogen content

(1.6 and 2.6 wt %) hydrofullerene mixtures demonstrated the presence of

only C60Hx species with no fragmented fullerenes. The 1.6 wt % sample

consists mostly of C60H18, C60H10, C60H6 and C60. Most likely,

hydrofullerenes with 2-10 hydrogens are less soluble in toluene; thus

their concentration in the initial powder is likely much higher than the

corresponding relative ion abundances in B.1. Note that the 1.6 wt %

sample was much less soluble than other samples. In good agreement

with IR spectroscopy data, MS analysis of 2.6 wt % (data not shown) and

3.4 wt % (Figure B.1) samples shows that they are composed mostly of

C60H18 (observed as protonated [C60H18 + H]+). The most abundant ions

in Figure B.1 for 3.4 wt % sample can be interpreted as protonated

molecules originating from C60H24, C60H30, C60H34, C60H42 and C60H50. An

increase in the degree of hydrogenation to 3.8 wt % results in a

significant increase in relative abundances of ions with hydrogen

numbers x > 24, especially for C60H34 molecular ions ([C60H34 + H]+); see

Figure B.2. Moreover, some low abundance ions from C59Hx and C58Hx

with x > 28 appear.

Fragmentation increases markedly in the samples hydrogenated to

5.0 and 5.3 wt % (Figure B.3). Major peaks in the spectrum of the 5.3 wt

% sample are from highly hydrogenated C60 with hydrogen numbers

above 40, with the highest relative abundance for C60H51+ ions (Figure

B.3 b). The most abundant fragmented fullerenes seem to follow two

different pathways. Several signals can be explained by CH2 loss from

C60H51+ ions, whereas some others, for example, C59H43

+ and C58H43+,

differ by the mass of one carbon.

The most important question arising from Figure B.3 is how to

relate a mass spectrum to the chemical composition of the sample: is the

fragmentation reaction a result of instrument induced effects or are

fragmented hydrofullerenes the result of synthesis? It is clear that more

133

m/z

780760740720700

C60H19+

C60H35+

C60H43 +

C60H51+

C60H31+

C60H25+

Figure B.2. APPI FT-ICR MS from the 3.8 wt % sample. The most abundant ions are assigned.

than one mechanism of fragmentation can be deduced from Figure B.3 a

and b, and the data analysis is further complicated by formation of both

radical cations and protonated molecules.

Mass scale-expanded segments demonstrate the resolved isotopic

cluster and increased abundance of fragmented fullerene ions (C58H43+

and C59H31+) generated from samples with higher hydrogen content

(Figure B.4). The absence of ions originating from the C60H18 molecule

([C60H18 + H]+) in the high hydrogen content sample is due to higher

degree of hydrogenation during synthesis.

Elemental compositions were assigned for all APPI FT-ICR mass

spectra obtained from samples with different degrees of hydrogenation.

The results of such analysis are shown in B.5.

134

m/z

780760740720700680660

C60H51+

C60H43+

C59H49+

C59H45+

C58H43+

C58H47+

C57H41+

C56H39+

C60H47+

(A)

m/z780760740720700680660

C60H51+

C59H49+

C58H47+

C59H43+

C58H43+

C57H45+

C60H47+

C60H43+

(B)

Figure B.3. APPI FT-ICR mass spectra from the samples with maximum hydrogenation (5.0 wt % (top) and 5.3 wt % (bottom)).

135

m/z739.901739.738739.574739.41739.246739.082

m/z739.738739.574739.41739.246739.082

m/z739.901739.738739.574739.41739.246739.082

m/z739.154739.133

APPI, 300 min

APPI, 1300 min

APPI, 5000 min

C60H19C59H1813C

C59H1813C2

C60H19

C58H43

C59H31

(A)

(B)

(C)

m/z739.901739.738739.574739.41739.246739.082

m/z739.738739.574739.41739.246739.082

m/z739.901739.738739.574739.41739.246739.082

m/z739.154739.133

APPI, 300 min

APPI, 1300 min

APPI, 5000 min

C60H19C59H1813C

C59H1813C2

C60H19

C58H43

C59H31

(A)

(B)

(C)

5.3 Wt%

3.4 Wt%

1.6 Wt%

C58H43+

C58H43+

C59H31+

C60H19+

C60H19+

C58H1713C2

+

C59H1813C+

Figure B.4. Scale-expanded m/z segment, 739-740 Da, for samples with different hydrogen contents.

136

52 54 56 58 60 62

15

20

25

30

35

40

45

50 3.8 Wt%

Hydro

gen n

um

ber

Carbon number

52 54 56 58 60 62

15

20

25

30

35

40

45

50

3.4 Wt%H

ydro

gen

Carbon

52 54 56 58 60 62

30

35

40

45

50

55

5.0 Wt%

Hydro

gen n

um

ber

Carbon number

52 54 56 58 60 62

38

40

42

44

46

48

50

52

54

565.3 Wt%

Abundance

Carbon number

3.4 Wt%

3.8 Wt%

5.0 Wt%5.3 Wt%

Carbon number Carbon number

Carbon numberCarbon number

Hyd

r og

en

nu

mb

er

Hyd

rog

en

nu

mb

er

Hyd

rog

en

nu

mb

er

Hyd

rog

en

nu

mb

er

Figure B.5. Carbon and hydrogen compositions obtained from APPI FT-ICR mass spectra (for mass spectral peaks with S/N > 7).

Fragmentation is clearly observed only for hydrofullerenes with a

high number of hydrogen atoms (more than 28). That observation is in

good agreement with our previous FD FTICR MS results. The second

observation is the chain of fragmentation products is not long: no

hydrofullerenes with fewer than 54 carbons were observed. The presence

of ions with composition C61Hx is most likely explained by addition of CH2

ions formed during fragmentation of some molecules. Similar addition of

C2 units was observed during fragmentation of pure C60 by a C2 loss

mechanism. Interestingly, the longest chain of fragmentation is not

observed for the sample with the highest degree of hydrogenation (see

also Figure B.3). Also note that the most abundant ions for the 5.0 wt %

sample originate from C59Hx with x = 44-48, whereas for the sample with

the highest degree of hydrogenation they originate from C60H50 by

137

formation of [C60H50 + H]+. The increased amount of highly hydrogenated

ions ([C60H50 + H]+) is in a good agreement with stronger hydrogenation of

this sample.

APPI versus FD FT-ICR MS

The 5 wt % sample was also analyzed by FD FT-ICR MS and the

results are compared to the APPI mass spectrum in Figure B.5. The mass

scale-expanded segments of similar mass spectra demonstrating resolved

isotopic patterns can be found in the inset of Figure B.4a of the present

paper (APPI) and in Figure 4 of the previous publication (FD).

Conditions for the FD FT-ICR mass analysis were optimized to

minimize fragmentation. Indeed, the chain of fragmentation products is

much shorter in Figure B.5 compared to our previously published

spectra for a sample of similar hydrogen content.111

The two mass spectra in Figure B.5 demonstrate some general

similarity but also major differences in relative ion abundances. For

APPI FT-ICR MS, the presence of mostly odd number of hydrogens, x, in

C60Hx is explained by the dominance of protonation over radical cation

formation. The most abundant ions in both mass spectra are C59Hx. The

FD mass spectrum shows maximum abundance for species with 42 and

44 hydrogen atoms, whereas the APPI mass spectrum has a maximum at

44 (taking into account that one hydrogen in APPI MS is from

protonation). Similarly, good agreement is observed for C58

hydrofullerene ions. Note that “parent” ions from C60H42-44 are present in

both spectra and show similar abundances relative to fragmentation

products.

The most prominent difference between the two observations is for

C60Hx with x > 50. The APPI mass spectrum shows a very high magnitude

peak corresponding to [C60H50 + H]+ ions, whereas the corresponding

138

m/z820800780760740720700680660

C59H42+

C60H42+

C60H46+

FD FT-ICR MS

of 5 Wt% sampleC58H42

+

C59H44+

m/z 820800780760740720700680660

C59H45+

C60H51+

C59H49+

C58H43+

C60H43+

APPI FT-ICR MS

of 5 Wt% sample

m/z820800780760740720700680660

C59H42+

C60H42+

C60H46+

FD FT-ICR MS

of 5 Wt% sampleC58H42

+

C59H44+

m/z 820800780760740720700680660

C59H45+

C60H51+

C59H49+

C58H43+

C60H43+

APPI FT-ICR MS

of 5 Wt% sample

Figure B.6. FT-ICR mass spectra 5.0 wt % samples: (top) FD; (bottom) APPI.

139

species in the FD mass spectrum is much lower in abundance. The APPI

mass spectrum also shows major peaks from ions likely produced as a

result of [C60H50 + H]+ fragmentation by a CH2 loss mechanism (see

Figure B.3a).

We propose the following interpretation of the data shown in

Figures B 3-5. Some of the fragmented fullerenes C58Hx and C59Hx are

produced during synthesis after prolonged hydrogenation periods, as

previously proposed.111 That is why the most abundant ions in both FD

and APPI FT-ICR mass spectra originate from C59H42-44 molecules.

Instrument-induced fragmentation is relatively weak in our new

optimized experiments (Figure B.5) for ions with fewer than 44 hydrogen

atoms but is seen for ions with a higher number of hydrogen atoms. For

example, [C60H50 + H]+ ions in Figure B.5 undergo fragmentation by CH2

loss. Note that this mechanism (CH2 loss) is clearly different from that

observed by FD FT-ICR MS (in which fragmentation occurred by loss of

C2H2 units111). The difference is most likely due to specific features of

each method: different ionization mechanism/ions, different pressure

and temperature conditions.

Low Mass Ions

APPI mass spectra of samples with 5 and 5.3 wt % also exhibit low

mass ions, 300 < m/z < 600. Most likely these ions form hydrocarbon

molecules as a result of C60 cage collapse. Partial collapse of

hydrofullerenes during prolonged hydrogenation was reported in our

previous publications, but analysis of fullerene fragments was limited to

IR spectroscopy and low-resolution matrix assisted laser

desorption/ionization time-of-flight mass spectrometry (MALDI TOF

MS).110 Because the sample synthesis was performed under conditions of

carbon-hydrogen reaction, relatively large fullerene fragments terminated

140

by hydrogen atoms could survive from the collapse. Most likely, these

molecules consist of hexagons and pentagons, but rings with seven and

eight carbons could appear as previously discussed.109

An APPI mass spectrum recorded with instrumental parameters

that provide significant enhancement of sensitivity in the low-mass

region is shown in Figure B.7. In general, the mass spectrum shows very

good agreement with MALDI-TOF mass spectra obtained previously for

one of HPLC fractions separated from a highly hydrogenated sample.

The common feature of these mass spectra is a sharp reduction in

abundance of ions with molecular weight below ~350 Da. Because the

synthesis of this sample was performed at high temperature (673 K), all

light hydrocarbons with low melting points (and high vapor pressures)

had evaporated. Preserved hydrocarbons show a broad distribution of

different compositions with a maximum near ~380-420 Da and the

highest abundance for C31H15+. In general, the highest abundance is

observed for the ions with an approximate carbon/hydrogen ratio of 2:1

(Figure B.7, inset).

m/z800720640560480400320

25 30 35 40 45 50

10

20

30

40

Hydro

gen

Carbon

Hyd

rog

en

nu

mb

er

Carbon number

Figure B.7. APPI FT-ICR MS of the 5.3 wt % sample under conditions that favor higher abundance of low-mass ions. Filled triangles denote higher-abundance species.

141

IR spectra recorded from this sample (not shown) show some

specific features in the region typically associated with C-H vibrations of

polycyclic aromatic hydrocarbons (PAH). Perhaps some of the peaks

shown in Figure B.7 originate from flat molecules. It is also likely that

collapse of C60 forms fragments with both pentagons and hexagons in the

structure. In that event, molecules with some curvature must form.

“Bowl-like” molecules similar to corannulene (C20H10) but of a larger size

are probably a significant part of the studied sample.

Elemental Composition of Hydrofullerene Mixtures

Considering the remarkably high stability and selectivity of C60H18

and C60H36 molecules during synthesis by chemical reduction methods,

one might anticipate that reaction of C60 with H2 gas would also lead to

formation of relatively high amounts of C60H18 and C60H36. That

prediction appears to be only partly true: both IR spectroscopy and APPI

FT-ICR MS show high selectivity for the synthesis of C60H18 (hydrogen

composition for the C60H18 compound is estimated to be ~2.4 wt %) only

on the initial stages of hydrogenation. In fact, the toluene-soluble

portion of the samples with 2.6 and 3.4 wt % of hydrogen appears to be

essentially pure C60H18 (see Figure B.1 for 3.4% sample analysis). That

result is especially interesting because C60H36 (~4.76 wt % of hydrogen)

was not especially abundant in samples with higher degree of

hydrogenation. That composition (C60H36) is limiting for several

hydrogenation methods; for example, Birch reduction does not produce

any hydrofullerenes with a higher number of hydrogen atoms.98 For

high-temperature reaction of C60 with hydrogen gas, the limitation is

obviously not valid and hydrofullerenes with hydrogen atom numbers up

to ~52-56 are formed. IR spectra of these complex mixtures are devoid of

sharp peaks and show only broad and poorly resolved features (not

142

shown). These highly hydrogenated species are less stable and mass

spectrometric analysis of samples that contain C60Hx with x > 36 is

complicated by significant fragmentation induced during mass analysis.

Remarkably, the fragmentation mechanism observed by APPI FT-ICR MS

(loss of CH2 units) is different from the dominant C2H2 loss previously

reported for FD FT-ICR MS.111 A similar fragmentation mechanism was

previously reported for C60H36,112 but the low resolution of their methods

did not allow the exact determination of the number of hydrogen atoms

in CHx units. The true mechanism of CH2 unit loss is not yet clear:

obviously only C-H units are present in C60Hx molecules. The source of

the second hydrogen atom and how the CH2 units are formed will be a

subject of future experiments. Probably the presence of not only radical

cations but also protonated molecules in APPI MS can lead to a different

fragmentation pathway.

In our prior studies, we also suggested that some fragmentation

with loss of CH units could occur during the synthesis of hydrofullerenes

under prolonged hydrogenation. Hydrogenated fragmented fullerenes,

C56-59Hx, are proposed to be present in our 5.0 and 5.3 wt % samples,

but analysis of those fragmentation products is further complicated by

fragmentation of highly reduced hydrofullerene ions during MS

experiments.

As seen in Figure B.3, the main fragment species are C59H43+ and

C59H49+ (which correspond most likely to protonated C59H42 and C59H48).

Both hydrofullerenes show their own set of fragmentation products

differing by increments of CH2. The C59H49+ ion could be a fragmentation

product from C60H51+ originating from fragmentation during MS analysis.

Conclusion

In summary, XRD, IR spectroscopy, and high-resolution mass

spectrometry serve to characterize the composition of samples obtained

143

from C60 hydrogenation over a broad range of reaction periods. For the

initial hydrogenation stages (hydrogen content in product molecules is

less than 3 wt %) mostly C60H18 species are found. Increased

hydrogenation period results in formation of hydrofullerenes with higher

number of hydrogens, such as C60H36. Prolonged hydrogenation

(formation of products with hydrogen content of ~5 wt %) demonstrates

the presence of highly reduced species (C60Hx with x > 40). Due to lower

stability of hydrofullerenes with high hydrogen content, molecular ions

from not only the highly reduced species but also from fragmented

fullerenes C54-59Hx were observed in the mass spectra. The origin of the

observed ions is not completely understood. Fragmentation of

hydrofullerenes could occur during the synthesis and during mass

spectrometric analysis. Unlike FD FT-ICR MS, fragmentation of

hydrofullerene ions in APPI follows a CH2 loss pathway. Nonetheless, we

believe that some of the hydrogenated fullerenes with fragmented cages

are formed during synthesis. Analysis of low mass ions (products of

fullerene cage collapse) revealed abundant hydrocarbon molecules with

carbon number of 25-45 and carbon number/hydrogen number ratio of

2/1.

The advent of APPI FT-ICR mass spectrometry for analysis of

hydrofullerene mixtures presents several significant advantages over

traditionally employed pulsed ionization techniques (electron impact

ionization, field desorption and MALDI). Instrument-induced

fragmentation in the APPI ion source should be minor relative to other

ionization methods. Both radical and protonated cations are formed in

the APPI ion source with the latter as the dominant ionization channel.

144

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52. Altgelt, K. H.; Boduszynski, M. M., Composition and analysis of heavy petroleum fractions. ed.; Marcel Dekker: New York, 1994; 'Vol.' p. 53. Chen, L.; Cottrell, C. E.; Marshall, A. G., Effect of Signal-to-Noise Ratio and Number of Data Points upon Precision in Measurement of Peak Amplitude, Position, and Width in Fourier Transform Spectrometry. Chemom. Intell. Lab. Syst. 1986, 1, 51-58. 54. Talyzin, A. V.; Tsybin, Y. O.; Purcell, J. M.; Schaub, T. M.; Shulga, Y. M.; Noreus, D.; Sato, T.; Dzwilewski, A.; Sundqvist, B.; Marshall, A. G., Reaction of Hydrogen Gas with C60 at Elevated Pressure and Temperature: Hydrogenation and Cage Fragmentation. J. Phys. Chem. A 2006. 55. Zhan, D. L.; Fenn, J. B., Electrospray mass spectrometry of fossil fuels. Int. J. Mass Spectrom. 2000, 194, (2-3), 197-208. 56. Rodgers, R. P.; Hendrickson, C. L.; Emmett, M. R.; Marshall, A. G., Reading Chemical Fine Print: Resolution and Identification of 3000 Nitrogen-Containing Aromatic Compounds from a Single Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrum of Heavy Petroleum Crude Oil. Energy & Fuels 2001, 15, (2), 492 -498. 57. Rudzinski, W. E.; Aminabhavi, T. M.; Sassman, S.; Watkins, L. M., Isolation and characterization of the saturate and aromatic fractions of a Maya crude oil. Energy Fuels 2000, 14, (4), 839-844. 58. Emmett, M. R.; Caprioli, R. M., Micro-electrospray mass spectrometry: ultra-high-sensitivity analysis of peptides and proteins. J. Am. Soc. Mass Spectrom. 1994, 5, (7), 605-613. 59. Rapp, U.; Staab, H. A.; Wunsche, C., Gas Phase Ion Energetics Data. NIST: 2005 60. Hagman, C.; Tsybin, Y. O.; Hakansson, P., Solution-phase deuterium/hydrogen exchange at a specific residue using nozzle-skimmer and electron capture dissociation mass spectrometry. Rapid Commun. Mass Spectrom. 2006, 20, (4), 661-665. 61. Loo, J. A.; Edmonds, C. G.; Smith, R. D., Tandem mass-spectrometry of very large molecules - serum-albumin sequence information from multiply charged ions formed by electrospray ionization. Anal. Chem. 1991, 63, (21), 2488-2499.

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BIOGRAPHICAL SKETCH

April 3, 1961 Born, Itazuke A.F.B., Fukuoka Japan Jan 1983 - Jan 2003 Active Duty United States Air Force May 2003 B.S., Analytical Chemistry Valdosta State University, Georgia March 2007 Ph.D., Analytical Chemistry Florida State University

Curriculum Vitae Jeremiah M. Purcell

Education

B.S., Analytical Chemistry, Valdosta State University, Valdosta, Georgia 2003 Ph.D., Analytical Chemistry, Florida State University Advisor: Professor Alan G. Marshall 2007

Teaching CHM 1045 General Chemistry I Lab, Florida State University Fall 2003 CHM 1045 General Chemistry I Recitation, Florida State University Spring 2004

Awards Senior Analytical Chemistry Award, American Chemical Society, Division of Analytical Chemistry 2003 Certified Analytical Chemistry B.S., American Chemical Society 2003 Senior Chemistry Student Award, Valdosta State University, Georgia 2003 Magna Cum Laude 2003 Gamma Sigma Epsilon Honor Society 2002

Professional Associations

American Chemical Society American Society for Mass Spectrometry

156

Publications and Scientific Activities Peer-Reviewed Publications

(1) Purcell, J.M.; Hendrickson, C.L.; Rodgers, R.P. and Marshall, A.G., Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry for Complex Mixture Analysis, Anal. Chem., 78, 5906-5912 (2006) (2) Fu, J.; Purcell, J.M.; Quinn, J.P.; Schaub, T.M.; Hendrickson, C.L.; Rodgers, R.P. and Marshall, A.G., External electron ionization 7 T Fourier transform ion cyclotron resonance mass spectrometer for resolution and identification of volatile organic mixtures., Rev. Sci. Instrum., 77, (22), 025102 (2006) (3) Talyzin, A.V.; Dzeilewski, A.; Sundqvist, B.; Tsybin, Y.O.; Purcell, J.M.; Marshall, A.G.; Shulga, Y.; McCammon, C. and Dubrovinsky, L., Hydrogenation of C60 at 2 GPa Pressure and High Temperature, Chem. Phys. Lett., 325, 445-451 (2006) (4) Talyzin, A.V.; Tsybin, Y.O.; Purcell, J.M.; Schaub, T.M.; Shulga, Y.M.; Noreus, D.; Sato, T.; Dzwilewski, A.; Sundqvist, B. and Marshall, A.G., Reaction of Hydrogen Gas with C60 at Elevated Pressure and Temperature: Hydrogenation and Cage Fragmentation, J. Phys. Chem. A, 110, 8528-8534 (2006) (5) Manning, T.J.; Land, M.; Rhodes, E.; Rudloe, J.; Phillips, D.; Lam, T.K.; Purcell, J.; Cooper, H.J.; Emmett, M. R. and Marshall, A.G., The Role of Extractions and Analysis in Identifying Bryostatins and Potential Precursors from the Bryozoan Bugula neritina, Natural Product Research, 19, (5), 467-491 (2005) (6) Wagberg, T.; Johnels, D.; Peera, A.; Hedenstrom, M.; Schulga, Y.M.; Tsybin, Y.O..; Purcell, J.M..; Marshall, A.G..; Noreus, D.; Sato, T. and Talyzin, A.V., Selective synthesis of the C3v isomer of C60H18, Organic Letters, 7, (25), 5557-5560 (2005) Presentations, Posters, and Abstracts (Presenter's name listed first) * Denotes Invited Talk *(1)Rodgers, R. P.; Smith, D. F.; Purcell, J. M.; Juyal, P.; Kim, D.-G.; Marshall, A. G., Recent Advances in the Characterization of Heavy Petroleum by FT-ICR Mass Spectrometry (oral) Molecular Structure of Heavy Oils and Coal Liquefaction Products, Lyon, France, 12-13 Apr (2007) *(2) Marshall, A.G.; Hendrickson, C.L.; Emmett, M.R.; Rodgers, R.P.; Nilsson, C.L.; Schaub, T.M.; Purcell, J.M. and Smith, D.F., High-Field Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: A Platform for "Omics", First International Symposium on Ultrahigh Resolution Mass Spectrometry for the Molecular Level

157

Analysis of Complex (BioGeo) Systems, GSF Neuherberg, Munich, Germany, November 6-7 (2006) *(3) Marshall, A.G.; Hendrickson, C.L.; Klein, G.F.; Purcell, J.M.; Schaub, T.M.; Smith, D.F.; Stanford, L A. and Rodgers, R.P., Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: The Platform for Petroleomics, 4th NCUT/WRI Conference on the Upgrading and Refining of Heavy Oil, Bitumen and Synthetic Crude Oil, Edmonton, Alberta, CANADA, September 25-27 (2006) *(4) Marshall, A.G.; Kim, D.-G.; Klein, G.C.; Stanford, L.A.; Purcell, J.M.; Schaub, T.M.; Smith, D.F.; Hendrickson, C.L. and Rodgers, R.P., Compositional Characterization of Petroleum by Ultrahigh-Resolution FT-ICR Mass Spectrometry with Multiple Ionization Sources, Symp. on Characterization, On-Line Monitoring and Sensing of Petroleum and Petrochemicals, 232nd Amer. Chem. Soc. Natl. Mtg., San Francisco, CA, September 10-14 (2006) *(5) Rodgers, R.P.; Klein, G.C.; Smith, D.F.; Purcell, J.M.; Schaub, T.M. and Marshall, A.G., Petroleomics and Mass Spectrometry, 17th Int'l Mass Spectrometry Conference, Prague, Czech Republic, August 27-September 1 (2006) *(6) Marshall, A.G.; Hendrickson, C.L.; Klein, G.F.; Purcell, J.M.; Schaub, T.M.; Smith, D.F.; Stanford, L.A. and Rodgers, R.P., Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: The Platform for Petroleomics, 7th Int'l Conf. on Petroleum Phase Behavior and Fouling, Asheville, NC, June 25-29 (2006) (7) Purcell, J.M.; Rodgers, R.P.; Hendrickson, C.L. and Marshall, A.G., Molecular Analysis of Asphaltenes by Negative Ion Atmospheric Pressure Photoionization (APPI) FT-ICR MS, 7th Int'l Conf. on Petroleum Phase Behavior and Fouling, Ashville, NC, June 25-29 (2006) *(8) Rodgers, R.P.; Kim, D.-G.; Purcell, J.M. and Marshall, A.G., Characterization of Sulfur Species in Petroleum Asphaltenes and Resins by FT-ICR Mass Spectrometry, 7th Int'l Conf. on Petroleum Phase Behavior and Fouling, Ashville, NC, June 25-29 (2006) (9) Purcell, J.M.; Rodgers, R.P.; Hendrickson, C.L.; Smith, D.F., and Marshall, A.G., Atmospheric Pressure Photoionization: Investigation of Proton Transfer in Complex Mixtures, 54th Amer. Soc. Mass Spectrom. Ann. Conf. on Mass Spectrometry & Allied Topics, Seattle, WA, May 27-June 2 (2006) (10) Kim, D.-G.; Purcell, J.M.; Rodgers, R.P. and Marshall, A.G, Isolation and Characterization of Crude Oil Asphaltenes and Coprecipitants by Negative-Ion Electrospray Ionization FT-ICR Mass Spectrometry, 54th Amer. Soc. Mass Spectrom. Ann. Conf. on Mass Spectrometry & Allied Topics, Seattle, WA, May 27-June 2 (2006)

158

*(11) Marshall, A.G.; Purcell, J.M.; Rodgers, R.P.; Hendrickson, C.L.; Tsybin, Y.O. and Talyzin, A., Atmospheric Pressure Photoionization (APPI) Fourier Transform Ion Cyclotron Resonance Mass Spectrometry for Analysis of Non-Polar Complex Mixtures, Symp. on Atmospheric Pressure Photoionization Mass Spectrometry for LC/MS, 57th Pitt. Con., 2006 Orlando, FL, March 12-17 (2006) *(12) Rodgers, R.P.; Klein, G.C.; Schaub, T.M.; Smith, D.F.; Kim, S.; Purcell, J.M.; Hendrickson, C.L. and Marshall, A.G., Petroleomics: Mass Spectrometry Returns to Its Roots, Frontiers beyond Biopharma, LabAutomation 2006, Palm Springs, CA, January 21-25 (2006) (13) Shul'ga, Y.; Talyzin, A.V.; Tsybin, Y.O.; Peera, A.A.; Schaub, T.M.; Purcell, J.M.; Marshall, A.G.; Sundqvist, B.; Mauron, P.; Zuttel, A. and Billups, W.E., Fragmentation and Collapse of C60 by Reaction with H2 Gas at Elevated Temperature and Pressure, Seventh Int. Workshop on Fullerenes and Atomic Clusters, St Petersburg, Russia, June 27- July 1 (2005) *(14) Purcell, J.M.; Rodgers, R.P.; Hendrickson, C.L.; Tsybin, Y.O.; Talyzin, A. and Marshall, A.G., Atmospheric Pressure Photoionization (APPI) Fournier Transform Ion Cyclotron Resonance Mass Spectrometry for Analysis of Non-Polar Complex Mixtures. APPI Symp. (oral), 53rd Amer. Soc. Mass Spectrom. Ann. Conf. on Mass Spectrom. & Allied Topics, San Antonio, TX, June 4-9 (2005) *(15) Rodgers, R.P.; Klein, G.C.; Schaub, T.M.; Purcell, J.M.; Kim, S.; Hendrickson, C.L. and Marshall, A.G., Petroleomics and Mass Spectrometry (oral), 53rd Amer. Soc. Mass Spectrom. Ann. Conf. on Mass Spectrom. & Allied Topics, San Antonio, TX, June 4-9 (2005) (16) Hockaday, W.C.; Purcell, J.M.; Marshall, A.G. and Hatcher, P. G., Carbon- Normalized Double Bond Equivalents as a Structural Determinant for Black Carbon in Natural Organic Matter Examined by FT-ICR Mass Spectrometry (poster), 53rd Amer. Soc. Mass Spectrom. Ann. Conf. on Mass Spectrom. & Allied Topics, San Antonio, TX, June 4-9 (2005) (17) Purcell, J.M.; Rodgers, R.P.; Hendrickson, C.L.; Quinn, J.P. and Marshall, A.G., Atmospheric Pressure Photoionization (APPI) FT-ICR Mass Spectrometry for Analysis of Heavy Petroleum (Poster), 5th N. Amer. FT-ICR MS Conf., Key West, FL, April 17-20 (2005) *(18) Rodgers, R.P.; Klein, G.C.; Stanford, L.A.; Purcell, J.M.; Kim, S.; Schaub, T.M. and Marshall, A.G., Petroleomics: Recent Advances in FT-ICR MS Characterization of Petroleum- Derived Materials (Oral), 5th N. Amer. FT-ICR MS Conf., Key West, FL, April 17-20 (2005)

159

*(19) Marshall, A.G.; Kim, S.; Purcell, J.M.; Schaub, T.M.; Smith, D. and Rodgers, R.P., Characterization of Petroleum by High Resolution Field Desorption / Ionization and Atmospheric Pressure Photoionization FT-ICR Mass Spectrometry, Methods and Techniques in Analytical Characterization for Fuel Science, 229th American Chemical Society National Meeting (Oral) (Fuel 94), San Diego, CA, March 13-17 (2005) (20) Purcell, J.M.; Rodgers, R.P.; Hendrickson, C.L. and Marshall, A.G., Atmospheric Pressure Photoionization (APPI) Fourier Transform Ion Cyclotron Resonance Mass Spectrometry for Analysis of Nonpolar Hydrocarbons, 52nd American Society for Mass Spectrometry Annual Conference on Mass Spectrometry and Allied Topics, Nashville, TN, May 23-27 (2004) (21) Fu, J.M.; Purcell, J.M.; Quinn, J.P.; Hendrickson, C.L.; Rodgers, R.P. and Marshall, A.G., A New 7 T FT-ICR Mass Spectrometer with External EI Source for Analysis of Non-Polar Volatiles, 52nd American Society for Mass Spectrometry Annual Conference on Mass Spectrometry and Allied Topics, Nashville, TN, May 23-27 (2004) (22) Manning, T.J.; Land, M.; Rhodes, E.; Rudloe, J.; Phillips, D.; Lam, T.-K. T.; Purcell, J.; Cooper, H.J.; Emmett, M.R. and Marshall, A.G., Elemental Analysis and Nanoparticles in the Synthesis of Bryostatin. Is There a Connection?, 227th American Chemical Society National Meeting, Anaheim, CA, March 28-April 1 (2004) (23) Land, M.; Rhodes, E.; Manning, T.J.; Lam, T.K.; Purcell, J.; Marshall, A.G.; Emmett, M.R.; Cooper, H.J.; Rudloe, J.; Phillips, D. and Newman, D., The Role of FT-ICR, MALDI-TOF-MS, and ICP-MS in Obtaining Bryostatin from the Bryozoa, Bugula Neritina, 55th Southeast Regional Meeting of the American Chemical Society, Atlanta, GA, November 16-19, (2003) (24) Rhodes, E.; Manning, T.J.; Lam, T.K.; Purcell, J.; Marshall, A.G.; Phillips, D. and Newman, D., Are Precursors to Marine Natural Products Ubiquitous in the Ocean?, 55th Southeast Regional Meeting of the American Chemical Society, Atlanta, GA, November 16-19, (2003)

petroleum analysis by atmospheric pressure photoionization fourier transform ion cyclotron

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