Introduction to Time-of-Flight Mass Spectrometry and DeconvolutionSpectrometry and Deconvolution

&

Nicholas Hall – SpeakerMark Libardoni, Pete Stevens, Joe Binkley

Life Science & Chemical Analysis CentreSt. Joseph, Michigan, USA

e-Seminar Goals

• Overview of a Time-of-Flight mass spectrometer– Comparison to scanning instruments– LECO’s TOF MS Instruments

• Spectral reproducibility• Fast spectral acquisition rates • Increased linear dynamic range

• Deconvolution OverviewDeconvolution Overview• Experimental Studies for:

– Sampling Rate– Deconvolution Capability– Usage as a High-Speed GC and GCxGC detector

Time-of-Flight Mass Analyzerg yA Time-of-Flight (TOF) is a non-scanning mass analyzerwhich emits pulses of ions (or transients) from the source.These pulses are accelerated so that the ions have equal

LECO’s Pegasus TOFMSThese pulses are accelerated so that the ions have equalkinetic energy as they are directed into a flight tube. Sincekinetic energy is equal to 1/2 mv2, where m is the mass ofthe ion and v is the ion velocity, the lower the ion's mass, thegreater the velocity and shorter its flight time. The travel timefrom the ion source through the flight tube to the detector,measured in microseconds, can be transformed to the m/zvalue through the relationships described above. Becauseall ion masses are measured for each transient, TOF massspectrometers offer high sensitivity as well as rapidacquisition. A non-scanning instrument such as TOF MSoffers many advantages including fast acquisition ratesoffers many advantages including fast acquisition rates,exceptional dynamic range, spectral continuity, the ability toacquire full mass range spectra without sacrificing speed orsensitivity, and capability to perform quantitative analysesacross a wide dynamic range in the presence of complexmatrices.matrices.

Quadrupolep

The strength and frequency of the RF field determines whether or not an ion of a certain mass passes through

Molecules

Quadrupole Ion Analyzer

Successful Ion Path

Detector

whether or not an ion of a certain mass passes through the rods (and is counted by the detector) or smashes into a nearby surface. For example, in a 120 volt field at a radio frequency of 2 MHz, only ions of 16 Daltons (Da) will navigate through the rods and into the detector. Heavier or lighter ions do not survive the journey to the

Ion Path

Electron Ion Beam

The quadrupole mass spectrometer is made with 4 rods of hyperbolic surfaces A direct current field is

g j ydetector. In this manner, you can control the mass of the ions that the detector collects.

rods of hyperbolic surfaces. A direct current field is applied to 2 rods and a radio frequency (RF) field is applied to the other 2 rods. These rods generate an electric field through which the ions can move.

Benefits of Quads and TOFsBenefits of Quads and TOFs• Quadrupole • Time-of-Flight

– Inexpensive

Robust

– Excellent Qualitative and Quantitative results in single run

– Robust

– Good for Qualitative and Quantitative work

– No Spectral Bias (skewing)

– Excellent Detection LimitsQuantitative work

– Enhanced Detection Limits when operating in SIM

Excellent Detection Limits

– Very Fast acquisition rates (up to 500 spectra/s)p g ( p p )

Sampling Ratep gQuadrupoles Time-of-Flight

• Scanning Instrument at 10,000 u/sec (~20 Hz)

Duty Cycle Time

• Non-Scanning Instrument– Full Mass Range Acquisition

All Masses are Collected– Duty Cycle Time

• Increase Scan Rate by Limiting Mass Range

– All Masses are Collected– Acquisition Rates up to 500

spectra/s (500 Hz)Limiting Mass Range– (40 – 200 amu)

Sampling Rate is important for properly defined peaks and deconvolution

Proper Sampling Ratesp p g• Literature defines the proper sampling rate of a

chromatographic detector to have an acquisition speed g p q pcapable of delivering at least 10 points across a fully resolved peak to deliver accurate quantitative data

• Therefore if you have a:– 1 second wide peak, you will need a detector speed of 10 Hzp , y p 0– 0.5 second wide peak (500 ms), you will need 20 Hz– 0.2 second wide peak (200 ms), you will need 50 Hz

0 1 second wide peak (100 ms) you will need 100 Hz– 0.1 second wide peak (100 ms), you will need 100 Hz– 0.05 second wide peak (50 ms), you will need 200 Hz

LECO Separation SciencesDelivering the Right Results

P 4D d HT T TOF HTPegasus 4D and HT- Fastest GCMS Available- Market’s only GCxGC-TOFMS

TruTOF HT- 2nd Fastest GCMS Available- All the advantages of TOF at quad

prices

Proper Sampling Ratesp p g• Most samples are complex and do not contain fully resolved

chromatographic peaks – therefore some method of deconvolution i d dis needed.

• LECO has published results showing that 18-20 data points are necessary for accurate quantitative deconvolution of overlapped peaks.

Spectral Bias (Skewing)

500

750

1000

Abu

nd.

4000

6000

8000

ensi

ty

500

750

1000 A

bund

.GC PeakTOFMS Scanning MS

60 80 100 120 1400

250

500

Rel

.

m/z

42.5 43.0 43.50

2000

4000

Inte

Time (sec)60 80 100 120 140

0

250Rel

.

m/z

1000

250

500

750

1000

Rel

. Abu

nd.

2000

4000

6000

8000

Inte

nsity

250

500

750

1000

Rel

. Abu

nd.

60 80 100 120 1400

m/z

750

1000

nd.

42.5 43.0 43.50

Time (sec)

6000

8000

60 80 100 120 1400

m/z

750

1000

nd.

60 80 100 120 1400

250

500

50

Rel

. Abu

n

/

42.5 43.0 43.50

2000

4000

6000

Inte

nsity

Time (sec)60 80 100 120 140

0

250

500

Rel

. Abu

m/z m/z( )m/z

Proper Sampling Ratep p g

Metolachlor 238Malathion 158

40 spectra/s

9 peaks locatedMalathion 158Fenthion 278Chlorpyrifos 199Parathion 291

9 peaks located

DCPA 301Cyanazine 68Isodrin 193T i hl t 269Trichloronat 269

Proper Sampling Ratep p g10 spectra/s

6 peaks located6 peaks located

Proper Sampling Ratep p g5 spectra/s

5 peaks located5 peaks located

Proper Sampling Ratep p g2 spectra/s

0 peaks located0 peaks located

40 spectra/s9 peaks located

10 spectra/s6 peaks located

2 spectra/s0 peaks located

True Signal True Signal DeconvolutionDeconvolutionA correlated set of ionsA correlated set of ions reaches the detector

erC

alip

True Signal Deconvolution

erC

alip

e

True Signal Deconvolution

erC

alip

e

T Si l D l tiA new correlated set of i h th d t t

True Signal Deconvolution

ions reaches the detector

erC

alip

e

T Si l D l ti

The first pack of correlated ions have apexed

True Signal Deconvolution

p pChromaTOF lays down a peak marker

erC

alip

e

T Si l D l tiTrue Signal Deconvolution

erC

alip

e

T Si l D l ti

The second pack of correlated ions have apexed

True Signal Deconvolution

p pChromaTOF lays down another peak marker

erC

alip

e

T Si l D l tiTrue Signal Deconvolution

erC

alip

e

T Si l D l tiTrue Signal Deconvolution

erC

alip

e

CoelutionCoelution of 3 Pesticidesof 3 Pesticides

Fenthion 278Chlorpyrifos 199Parathion 291

< 550 ms >

Spectral Spectral CoelutionCoelution of Pesticidesof Pesticidespp

* *FenthionChlorpyrifosParathion*

*

* ** ***

*

**

**

Spectral Spectral DeconvolutionDeconvolution of Pesticidesof Pesticides

Deconvoluted SpectraDeconvoluted Spectraof Chlorpyrifos

NIST Library Spectraof Chlorpyrifos

For More InformationFor More Information

Contact LECO at:

World Headquarters/United StatesIn United States: 800-292-6141 or 269-985-5496

Outside U.S.A.: 269-983-5531

Email: info@leco comEmail: info@leco.comwww.leco.com