Unique Capabilities of Gas Chromatography –

Vacuum Ultraviolet Spectroscopy

Kevin A. Schug, Ph.D.

Department of Chemistry & Biochemistry,

The University of Texas at Arlington, Arlington TX

Disclaimer: KAS is a member of the Scientific Advisory Board for

VUV Analytics, Inc.

Characteristics of VGA-100 for GC-VUV

Make-up gas mitigates/alleviates band-broadening

Nondestructive; could be placed in-line with MS

Full range 120 – 240 nm data acquisition at up to 100 Hz

VUV/UV source lamp (D2); stable signal and robust

Thermostatted flow cell (up to 320 ᵒC)

Carrier and make-up gases (He, H2, N2, Ar) largely VUV transparent.

Post-run processing for universal or selective detection; library spectral matching; etc.

Analyte-specific absorption based on Beer’s Law principles; Qualitative and quantitative analysis (wide linear range)

Schug et al., Anal. Chem. 2014, 86, 8329-8335.

What Has Been Published?Intro/Gasoline, Anal. Chem. 2014, 86, 8329.

Permanent Gases, J. Chrom. A 2015, 1388, 244.

Pesticides, J. Chrom. A 2015, 1389, 120.

FAMEs, Food Chem. 2016, 194, 265; J. Agric. Food Chem. 2016, 64, 1422 (Armstrong); J. Chromatogr. A 2017, In Press (Mondello GCxGC)

Time Interval Deconvolution/Gasoline PIONA, Polychlorinated biphenyls, Anal. Chem. 2016, 88, 11130; J. Chromatogr. A 2017, 1490, 191.

Dimethylnaphthalenes, Limits of Deconvolution, Jet Fuel, and Computation, Anal. Chim. Acta 2016, 945, 1-8

Diesel, Anal. Chem. 2016, 88, 3031 (Zimmermann GCxGC); Anal. Chem. 2016, 88, 5809 (Harynuk);

Breath Volatiles, J. Chrom. A 2016, 1464, 141 (Zimmermann GCxGC)

Pseudo-Absolute Quantification, Anal. Chim. Acta 2017, 953, 10.

Designer Drugs and Computation, Anal. Chim. Acta 2017, 971, 55.

Water in Solvents, The Column (LCGC) Feb. 17, 2017, 9-13.

GC-VUV Review, J. Sep. Sci. 2017, 40, 138.

Key Features Highlighted• Unique, but class-similar spectra• Excellent complementarity to MS

– Isomers/isobars, cis-/trans-, labile, low m.w.

• Universal and selective detection– Full acquisition Spectral filters

• Deconvolution of coeluting analytes– Additive absorption– Automated speciation and classification

• Respectable quantitative performance– Low/mid-pg on column– Pseudo-absolute quantitation

• Supported with theoretical computations

Paraffins (C5-C9)

Isoparaffins

Naphthenes

Fuels Analysis

(linear alkanes)

(branched alkanes)

(cyclic alkanes)

Absorption profiles from 125 – 240 nm shown

Olefins(unsaturated alkanes)

Aromatics

Gasoline Proficiency Standards

30 m nonpolar column Oven ramp: 30 0C 10min, 7 0C/min 200 0CInjector temperature: 250 0C Injection volume: 0.3 uLSplit Ratio: 50:1 Carrier flow rate: 1 mL/min

125 – 160 nm170 – 200 nm

Spectral Filters

Samples courtesy of Valero

DeconvolutionWalsh et al., Anal. Chem. 2016, 88, 11130-11138

PIONA Analysis of GasolineMass % or Volume % of … ASTM Method(s)

Paraffins

ASTM D6839

ASTM D6730

Isoparaffins

Naphthenes

Olefins ASTM D6550

ASTM D1319Aromatics ASTM D5580, D5769

Total Saturates

Oxygenates ASTM D4815 ASTM D5599 ASTM D5845

Benzene

ASTM D5580

ASTM D5769 ASTM D3606Toluene

Ethyl Benzene

Xylenes

GC-VUV can determine all in one 35 min analysis using TID

Time Interval Deconvolution (TID)

Automated Compound Classification and Speciation from Complex Mixtures

Finished Gasoline Characterization (PIONA analysis)ASTM D8071 (March, 2017)Walsh et al., Anal. Chem. 2016, 88, 11130-11138

Polychlorinated Biphenyls in Aroclor MixturesQiu et al., J. Chromatogr. A 2017, 1490, 191-200.

Requirements for TID

• Reference library spectra for analytes of interest

– e.g. PIONA molecules

– Segregated by class

– Some unknowns allowed

• Assigned retention index for each compound

• Assigned relative response factor for each compound/class

Walsh et al., Anal. Chem. 2016, 88, 11130-11138

TID Workflow

Set Retention Index Tolerance

(e.g. ± 25 – 40)

Set Time Interval for TID Analysis

(e.g. 0.03 min)

Calculate total absorbance of 1st TI

(note RI)

Select reference library in RI window

Perform tiered library search (1, 2, 3…

components) and deconvolution

Assign area response to class/species and proceed to next TI

Calculate mass % using relative response factors (RRF) for each class/species detected

OUTPUT

Time Interval Deconvolution

Walsh et al., Anal. Chem. 2016, 88, 11130-11138

GC-VUV vs. ASTMWalsh et al., Anal. Chem. 2016, 88, 11130-11138

GC-VUV Analysis of Commercial Aroclors

Aroclor 1254

Aroclor 1242

Qiu et al., J. Chromatogr. A 2017, 1490, 191-200.

209 Congeners

PCB Congener Mix (EPA Method 525.2)

• Distinctive absorbance, 185-210 nm and 140-150 nm

• Increasing λmax with increasing chloro-substitution

Qiu et al., J. Chromatogr. A 2017, 1490, 191-200.

Homologue Composition of Aroclors by TID

Chlorinated Biphenyl 1221 1232 1016 1242 1248 1254 1260 1262

Mono 62.957 37.92 1.149 1.12 0.294 0 0.035 0.011

Di 33.375 27.346 22.124 19.229 3.626 0.18 0.056 0.54

Tri 2.711 20.19 50.351 42.481 24.943 0.887 0.108 1.5

Tetra 0.369 11.711 25.023 28.854 49.608 16.214 0.694 0.964

Penta 0.483 2.718 1.343 8.018 20.134 55.318 14.23 4.854

Hexa 0.105 0.108 0.01 0.298 1.287 25.312 47.819 34.145

Hepta - 0.007 - - 0.101 2.079 31.401 43.626

Octa - - - - 0.007 0.01 5.276 13.116

Nona - - - - - - 0.381 1.245

Deca - - - - - - - -

Total chlorine (%)

20.39 (21)

31.77 (32)

40.97 (41)

42.50 (42)

47.71(48)

55.02 (54)

60.28 (60)

61.43 (62)

Qiu et al., J. Chromatogr. A 2017, 1490, 191-200.

Pseudo-Absolute Quantitation

Absorption cross-section is a physical property of a molecule

GC Injection DiagnosticsBai et al., Anal. Chim. Acta 2017, 953, 10-22.

Pseudo-Absolute Quantitation• Based on analyte cross-section (120 – 240 nm)• Beer’s Law principles

• Peak area (PA) depends on:– Amount of analyte placed on column (Ncol) ?– Cross-section over wavelength range (Σav) ✓

– Total flow rate through the cell (F) ✓

– Detector sampling rate (R) ✓

– Cell volume and path length (d) ✓

colav

m

j

j NF

dRAPA

)10ln(

1

1

int,

Bai et al., Anal. Chim. Acta 2017, 953, 10-22.

A = εbc

Absorption Cross Sections

19

Benzene

Bai et al., Anal. Chim. Acta 2017, 953, 10-22.

GC DiagnosticsErrors in sample introduction for GC

20

Variables Split/Splitless

Values

Syringe size Splitless 10 µL, 0.5 µL

Injection volume Splitless 0.1, 0.4, 0.6, 0.8, and 1 µL

Sampling time Splitless 0.25, 0.5, 1.0 and 1.5 min

Septum purge flow rate Splitless 1.0, 3.0, and 5.0 ml/min

Split ratio Split 2:1, 5:1, 10:1, 20:1, 100:1, and 200:1

Benzene/Toluene mixture

Bai et al., Anal. Chim. Acta 2017, 953, 10-22.

Sampling Time (Splitless)(0.2 µL injection of a 150 ng/µL solution of benzene)

GC parameter settings Theoretical

mass (ng)

Actual mass

(ng)

Efficiency %

Sampling

Time

(1 ml/min purge flow)

0.25 min 30 14.7 ± 0.3 49± 1

0.50 min 30 29.0 ± 0.9 97 ± 3

1.00 min 30 32.3 ± 0.5 108 ± 2

1.50 min 30 33.4 ± 0.9 111 ± 3 21

Injection volume (Splitless)

(1 min sampling time with 10 µL syringe )

GC parameter settings Theoretical

mass (ng)

Actual mass

(ng)

Efficiency %

Injection volume

0.1 µL 15 19.2 ± 0.3 129 ± 2

0.4 µL 60 65.4 ± 0.4 109.0 ± 0.7

0.6 µL 90 103.7 ± 0.5 115.3 ± 0.6

0.8 µL 120 151.5 ± 15 126 ± 12

1.0 µL 150 185.1 ± 0.1 123.4 ± 0.722

Split ratio(0.6 µL injection volume of the 150 ng/µL benzene standard)

GC parameter settings Theoretical

mass (ng)

Actual mass (ng) Efficiency %

Split ratio

(0.6 µL

injection)

2:1 45 18.5 ± 0.4 42.0 ± 0.9

5:1 18 10 ± 1 57 ± 5

10:1 9 5.6 ± 0.3 62 ± 3

20:1 4.5 2.9 ± 0.3 65 ± 6

100:1 0.9 0.7 ± 0.1 84 ± 11

200:1 0.45 0.38 ± 0.05 84 ± 1023

Correction Curves

10 µL syringe in autosampler

Bai et al., Anal. Chim. Acta 2017, 953, 10-22.

Calibration Curve

Bai et al., Anal. Chim. Acta 2017, 953, 10-22.

Internal Standard-Based Pseudo-Absolute Quantitation

1,1,

2,2,

1

2

colav

colav

N

N

PA

PA

colav NF

dRPA

)10ln(

1

If we want to determine unknown compound 2 with known cross-section, include known compound 1 (IS) with known cross-section

IS-based Calibrationless QuantitationPrepared

benzene

concentration

25 ng/µL 50 ng/µL 100 ng/µL 150 ng/µL 200 ng/µL400

ng/µL

Expected

Benzene on

Column (ng)

5 10 20 30 40 80

Expected IS*

on Column (ng)30 30 30 30 30 30

Benzene in

Detector (ng)5.7 ± 0.1 11.7 ± 0.2 21.6 ± 0.3 32 ± 2 42 ± 2 87 ± 5

Toluene in

Detector (ng)33.0 ± 0.5 34.0 ± 0.4 33.0 ± 0.5 33 ± 2 33 ± 1 35 ± 2

Determined

benzene in

sample (ng/µL)

26.3 ± 0.7 51.8 ± 0.6 99.36 ± 0.07 144.1 ± 0.6 194.6 ± 0.4 378 ± 2

*Toluene IS Bai et al., Anal. Chim. Acta 2017, 953, 10-22.

FM-GCxGC-VUV of Complex Mixtures

Zoccali et al., J. Chromatogr A 2017, 1497, 135-143.

Biodiesel

12 mL/min to VUV

Cross-Sections

Compound Average Cross Section

(cm2/molecule)

Methyl butyrate 4.5 (±0.2) x 10-17

Methyl hexanoate 7.5 (±0.3) x 10-17

Methyl octanoate 8.1 (±0.3) x 10-17

Methyl decanoate 1.12 (±0.04) x 10-16

Methyl undecanoate 1.21 (±0.04) x 10-16

Methyl laurate 1.13 (±0.04) x 10-16

Methyl tridecanoate 1.86 (±0.06) x 10-16

Methyl myristate 1.28 (±0.04) x 10-16

Methyl myristoleate 1.05 (±0.03) x 10-16

Methyl pentadecanoate 1.07 (±0.04) x 10-16

Methyl cis-10-pentadecenoate 2.03 (±0.06) x 10-16

Methyl palmitate 1.54 (±0.06) x 10-16

Methyl palmitoleate 1.75 (±0.06) x 10-16

Methyl heptadecanoate 1.61 (±0.06) x 10-16

Methyl cis-10-Heptadecanoate 2.60 (±0.09) x 10-16

Compounds Average Cross Section

(cm2/molecule)

Methyl octadecanoate 1.99 (±0.07) x 10-16

Methyl oleate 2.43 (±0.09) x 10-16

Methyl elaidate 1.92 (±0.08) x 10-16

Methyl linoleate 1.64 (±0.07) x 10-16

Methyl linolelaidate 1.63 (±0.07) x 10-16

Methyl linolenate 1.45 (±0.07) x 10-16

Methyl ɣ-linolenate 1.84 (±0.06) x 10-16

Methyl eicosanoate 1.92 (±0.07) x 10-16

Methyl cis 11 eicosenoate 1.91 (±0.08) x 10-16

Methyl cis 11,14 eicosadienoate 1.92 (±0.07) x 10-16

cis 11,14,17 eicosatrienoic acid

methyl ester 1.12 (±0.04) x 10-16

cis 8,11,14, eicosatrienoic acid

methyl ester 1.12 (±0.04) x 10-16

Methyl arachidonate 1.12 (±0.04) x 10-16

Methyl cis 5,8,11,14,17

eicosapentaenoate 1.12 (±0.04) x 10-16

Methyl cis 4,7,10,13,16,19

docosahexaenoate 1.12 (±0.04) x 10-16

Zoccali et al., J. Chromatogr A 2017, 1497, 135-143.

BAMEs and FAMEs in BiodieselBAMEs Bio-diesel

Compounds

Amount of mass at

detector (g)

Corrected

concentration in

injected sample (mg

L−1)

Amount of mass at

detector (g)

Corrected

concentration in

injected sample

(mg L−1)

Methyl undecanoate 1.39E-08 146.6

Methyl laurate 1.54E-08 162.8

Methyl tridecanoate 1.14E-08 120.8

Methyl myristate 1.60E-08 169.7

Methyl pentadecanoate 2.15E-08 226.9

Methyl palmitate 1.53E-08 162.1 1.57E-08 2814.3

Methyl palmitoleate 1.61E-08 170.3

Methyl heptadecanoate 1.82E-08 192.8

Methyl octadecanoate 1.34E-08 142.1 2.08E-09 374.9

Methyl oleate 9.15E-09 96.8 4.27E-08 7673.3

Methyl elaidate 1.27E-08 134.4

Methyl linoleate 1.58E-08 166.7 2.64E-08 4743.8

Methyl ɣ-linolenate 2.16E-09 387.9

Methyl eicosanoate 1.78E-08 188.0 8.95E-10 160.9

Methyl cis 11 eicosenoate 8.82E-10 158.7

Zoccali et al., J. Chromatogr A 2017, 1497, 135-143.

Summary• GC-VUV is a complementary tool to MS

• Unique class-specific signatures

• Isobars/Isomers – easily differentiated

• Beer’s law facilitates qualitative and quantitative analysis

• Deconvolution of co-eluting species– Less burden on separation

• Rapid compound classification and speciation of complex mixtures by TID

• Support by theoretical computations developing

The Next Generation: VGA-101

Wider spectral range 120 – 430 nm

The Next Generation: VGA-101

Wider spectral range 120 – 430 nm

Benzo(a)fluoranthene Benzo(b)fluoranthene

Benzo(b)fluoranthene Perylene

The Next Generation: VGA-101

Temperature stability increased to 430 oC

2 – 3x in sensitivity (IDL <10 pg on column)

Many Thanks!

VUV Analytics, Inc.:Clark JerniganSean Jameson

Dr. Dale HarrisonDr. Phillip Walsh

Dr. Jonathan SmutsJack Cochran

Dr. Hui FanDr. Doug D. Carlton, Jr.

Dr. Ines SantosDr. Changling Qiu

Dr. James MaoLing Bai

Jamie SchenkIan Sawicki

Courtney WestonAllegra Leghissa

Friends from CZ:Prof. Vladimir Havlicek

Prof. Karel LemrDr. Petr Frycak

Dr. Ludovit Skultety

GWU: Dr. Ira Lurie and students

Valero: Dr. Manuel Garbalena

Messina: Dr. Mariosimone Zoccali

Prof. Peter TranchidaProf. Luigi Mondello

UTA: Prof. Peter Kroll

Shimadzu:Dave JorissenDave Whitten