how to use tof and q-tof mass spectrometers - agilent to use tof... · how is accurate mass used?...
TRANSCRIPT
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
Mass extraction window:
+/- 0.00092 Da.
= +/- 5 ppm
EIC 184.0341 dibenzothiophene
TIC
Crude oil target analysis – target analysis
Problem: identify and quantify dibenzothiophene
Resolution 12,000
dibenzothiophene
Mass extraction window:
+/- 5 ppm
EIC 184.0341
TIC
Crude oil target analysis – target analysis
Problem: identify and quantify dibenzothiophene
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
Flurenol methyl ester
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
What to do when you run out of resolution? Use MS/MS
Flurenol methyl ester
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
What to do when you run out of resolution? Use MS/MS
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
+ESI EIC(400.4064) Scan Frag=180.0V crude_oil_spless_DG_08.d Smooth
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
+ESI EIC(400.4064) Scan Frag=180.0V crude_oil_spless_DG_08.d Smooth
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