How to Use TOF and Q-TOF Mass Spectrometers - Agilent to Use TOF... · How is accurate mass used?...

How to Use TOF and Q-TOF

Mass Spectrometers

October 2011

What do TOF and Q-TOF offer?

TOF • Fast scanning of full spectrum

• High resolution full scan spectra

• Accurate mass measurements

Q-TOF • Fast scanning of full spectrum

• High resolution full scan spectra

• Accurate mass measurements

• MS/MS product ion spectra

• Full scan product ion spectra with high resolution and accurate

mass

How is accurate mass used? Extracted ion chromatograms - EIC

Each point of EIC represents

the sum of ions in mass peak

within a specified mass range

Mass peak

m/z

m2

Chromatogram – EIC m1

m1-extracteded

Extraction window

Crude oil target analysis – target analysis

Problem: identify and quantify dibenzothiophene

Interferences

TIC

Mass extraction window:

+/- 0.5 Da.

= +/- 2717 ppm

EIC 184.0341 dibenzothiophene

Resolution 12,000


+/- 0.00092 Da.

= +/- 5 ppm

EIC 184.0341 dibenzothiophene

TIC



Resolution 12,000

dibenzothiophene


+/- 5 ppm

EIC 184.0341

TIC



Resolution 12,000

• No interferences

• Better low level peak integration

• Better quantitation

• Better confirmation

Fast scanning of full spectrum “Speed” enhances deconvolution

Time

Deconvolution Requires: • Retention time difference to > (1/10) W1/2

• At least one mass that is different for each component

• Peak sampled < to/2

to

Example:

• W1/2 = 1 second

• to > 0.1 second

• Peak sampled < 0.05 second

= 20 spectra/second

High data rate = better deconvolution

Slow data rate will not

pick each peak apex Time Fast data rate will allow

deconvolution of closely

eluting peaks

Time

High resolution, mass accuracy and scan speed Using factional masses for deconvolution

TOF and Q-TOF

• Fast scan rates >50 spectra/second facilitate deconvolution of peaks with

small retention time differences

• Using high mass accuracy spectra with fractional masses rather than

integer masses provides:

• more masses that are distinct between the two co-eluting compounds

• better deconvolution particularly at low levels

• better sensitivity

Deconvolution – identify unknown residues Jalapeno Pepper Extract – GC/TOF Analysis

Unknowns analysis – one page for everything

TIC & component chromatograms for hits

List of hits after deconvolution

and library searching

(no RT filtering)

TIC and extracted

ions of o-phenylphenol

Data file

Retention time

of deconvoluted

components

Deconvoluted spectrum

of o-phenylphenol

Library spectrum

Measured spectrum

240.1218

240.0785

Flurenol methyl ester

m/z = 240.0781

Mass error = 1.7 ppm

Dimetilan

m/z = 240.1217

Mass error = 0.4 ppm

~13,500 resolution FWHM

How much resolution is enough? Relative abundance of co-eluting compounds affects the result

Dm = 0.043 Da.

240.1184

240.0780


m/z = 240.0781

Mass error = -0.4 ppm

Dimetilan

m/z = 240.1217

Mass error = -13.7 ppm

A resolution of 13,500 is not

enough - larger ratios require

more mass resolution, MS/MS

or better GC separation

How much resolution is enough? Abundance Ratio - flurenol methyl ester:Dimetilan = 10:1

• Large shifts in measured mass reduces value for

confirmation – necessitates larger extraction windows

• Large shifts in measured mass changes EIC as peak elutes

because the ratio of analyte to matrix changes and therefore

the mass shift changes

What occurs when the measured mass shifts

• MS/MS product ions are generally well separated in mass

• Therefore - product ion masses do not shift due to lack of

resolution

• Why use Q-TOF rather than triple quadrupole?

• Sometimes qualifier ions have low abundance

• Accurate mass measurement of quantitation ion offers more

confirmatory information than using a low abundance qualifier ion

What to do when you run out of resolution? Use MS/MS



Flurenol methyl ester MS/MS 10 ev

4 x10

0

0.5

1

1.5

2

2.5

3

3.5

181.064470

153.069508 225.053192 208.051502

Counts vs. Mass-to-Charge (m/z) 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235 240

Dimetilan

MS/MS 10 ev

Dimetilan 5 x10

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9 72.044293

170.092686 95.059779

Counts vs. Mass-to-Charge (m/z)

55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235 240

mp = 240

mp = 240

MS/MS 10 ev

MS/MS 10 ev

Quant ion

Qualifier ion

Quant ion

Qualifier ion

Confirmation is limited by low

abundance of qualifier ion

4 x10

0

0.2

0.4

0.6

0.8

1

181.064586

72.044103 153.069718 208.052118 170.091272

Counts vs. Mass-to-Charge (m/z) 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240


Flurenol methyl ester + Dimetilan 1:1

Flurenol methyl ester +Dimetilan 10:1

MS/MS 10 ev

mp = 240

mp = 240

4 x10

0

0.2

0.4

0.6

0.8

1

1.2 72.044223 181.064453

170.092205 95.060038 153.069997 225.097591

Counts vs. Mass-to-Charge (m/z) 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235 240

Dimetilan

C3H6NO

Δ = -1.67 ppm

FME

C13H9O

Δ = 0.80 ppm

mp = 240

MS/MS 10 ev

Can use the quant ion

for confirmation and

better sensitivity

Crude oil: steranes – MS Problem: identify and quantify isomers

EIC 217.1951

EIC 400.4064

+/- 5 ppm

High resolution, accurate mass does

not always help to obtain required

selectivity

5 x10

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

+ESI EIC(217.1951) Scan Frag=180.0V crude_oil_spless_DG_08.d Smooth

4 x10

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4


Counts vs. Acquisition Time (min)

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 25 25.5 26 26.5 27 27.5 28 28.5 29 29.5 30 30.5 31 31.5 32 32.5

EIC 400.4064 +/- 5 ppm

Accurate mass does not

always provide the required

selectivity

EIC 217.1951 +/- 5 ppm Resolution 12,000

Crude oil: steranes – MS/MS Problem: identify and quantify isomers

MS: EIC 400.4064

MS/MS: 400 > 217.1951 • Better selectivity

• Improved S/N

Isomers

4 x10

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2


3 x10

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

+ESI EIC(217.1951) MS(all) Frag=180.0V crude_oil_MSMS400_spless_DG_01.d Smooth

Counts vs. Acquisition Time (min)

25.7 25.8 25.9 26 26.1 26.2 26.3 26.4 26.5 26.6 26.7 26.8 26.9 27 27.1 27.2 27.3 27.4 27.5 27.6 27.7 27.8 27.9 28

EIC 217.1951 +/- 5 ppm

MS/MS: 400 > 217.1951

Isomers

Resolution 12,000

Background

reduced

X5000

MS/MS accurate mass EIC 10 pg sample – resolution 13,000

EIC 192.9150 +/- 20ppm

die

ldrin

endrin

die

ldrin

EIC

262.8564 ±20 ppm

EIC

262.8564 ±0.5 Da.

Full scan MS

High resolution/accurate mass

MS/MS 263>192.9150

High resolution/accurate mass

Resolution and accurate mass are insufficient – MS/MS solves the problem

endrin

Summary

• The resolution and mass accuracy available from a TOF

instrument can solve many analytical problems

• For some analyte and matrix combinations there is not

enough mass resolution to confirm and quantify over the

required analyte/matrix concentration range

• Q-TOF MS/MS provides constant measured product ion

mass values over a larger analyte concentration range

than TOF alone when there is not enough resolution

Thank you for your attention

How to Use TOF and Q-TOF Mass Spectrometers - Agilent to Use TOF... · How is accurate mass used?...

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