Ion Mobility - Mass Spectrometry
as a new approach for the screening
of pesticide residues in food
Laure Joly
Séverine Goscinny, Romain Touilloux, Edwin De Pauw and Gauthier Eppe
Mass Spectrometry Laboratory, Department of Chemistry, University of Liège, Belgium
Service Denrées Alimentaires, Scientific Institute of Public Health, Belgium
Euroanalysis 16, September 2011
Pesticides
Ø Rich in diversity Chemical structure, solubility, volatility…
= substances or mixture intended for preventing, destroying,
repelling or mitigating any pest
Ø Currently, there are more than 1,055 pesticides registered1
1 U.S. Environmental Protection Agency
2
Challenge for the analyst:
Ø Hidden in complex food matrices
Methods
3
Have to be viable for the lab
Multiresidue Methods • Generic • Easy • Fast
Selected Reaction Monitoring
(using triple quadrupole)
• Quantitative
• Simultaneous determination
of a restricted number of
compounds
• Only used with target pesticide
0
10
20
30
40
50
60
70
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Num
ber o
f con
curr
ent t
rans
ition
s
Time (min)
ESI+ ESI-
UPLC, column Waters Acquity BEH C18 (2.1 * 100 mm I.D., 1.7µm)
But demands for new pesticides detection is constantly growing …
4
Screening method (ToF-MS)
• Qualitative
• Simultaneous determination of unlimited number of compounds
• High resolution technique and excellent sensitivity in full scan mode
• Enables to non-target analysis (identification of unknown peaks in the sample)
• No univocal identification
• Qualitative data (present or not) requiring a high level of confidence
How can we improve screening efficiently?
However
Methods
By using a 3rd dimension of separation:
ION MOBILITY
5
Extended
Compact
Ion Mobility (IM)
Traditional ion mobility cell
Electric field
Focusing rings
Ions enter cell
To detector
Extended slow
Compact fast
Drift time or
mobility time
6
Separation is driven by an electric field applied to an ion mobility cell
which contains a neutral gas at a controlled pressure (~3.0 mbar)
7 7
Triwave ion guide
.
Ring electrode
Transmission and resolution are not compromised
Giles, K., et al., RCM, 2004. 18(20): p. 2401-14.
Ion propulsion is produced by superimposing
- a radially confining RF voltage generate a trap along the z-axis
- a travelling voltage wave on which the ions can surf
travelling voltage wave
• Potential difference CE1 • Potential difference Bias
• Potential difference CE2
Wave Amplitude Wave velocity Collision gas Pressure of the collision gas
The Q-TOF type instrument (Synapt G2)
within IM
CE1 BIAS CE2 IMS
Trap Transfer
P ≈ 10-2 mbar P ≈ 5.10-1 mbar P ≈ 10-2 mbar
9
Synapt G2 HDMS @ Waters
Ion mobility cell
ESI
Quadrupole + Ion Guide
ToF
6.0 6.5 7.0 7.50.0
0.2
0.4
0.6
0.8
1.0
Temps de mobilité (ms)
Quinalphos
Phoxim
Quinalphos + Phoxim
Ω = 125 Å2
Ω = 122 Å2
C12H15N2O3PS
10
Discrimination between isomers
Mobility time (ms)
In this case parameters will optimized to separated these 2 molecules
m/z = 299.0619
6.0 6.5 7.0 7.50.0
0.2
0.4
0.6
0.8
1.0
Temps de mobilité (ms)
Quinalphos
Phoxim
Quinalphos + Phoxim
6.0 6.5 7.0 7.50.0
0.2
0.4
0.6
0.8
1.0
Temps de mobilité (ms)
Quinalphos
Phoxim
Quinalphos + Phoxim
11
Bias
Helium cell Pressure IMS cell pressure
Determination of used gas travelling voltage wave
Wave height Wave velocity
Optimization of mobility cell parameters
Plackett-Burman experimental design followed
by a Central Composite Design were carried out
on most influential parameters
3 responses Intensity Resolution Relative drift time
Selection of 4 representative pesticides
12
Separation of 2 main pesticide classes
Two classes of pesticides were found to form characteristic mobility-mass correlation curves
0.00
2.00
4.00
6.00
8.00
130.0 180.0 230.0 280.0 330.0 380.0 430.0m/z
Carbamates
Organophosphates
Mob
ility
tim
e (m
s)
Ion mobility Pesticide screening
13
a. Does ion mobility have the potential to separate target ions from matrix interferences?
b. Can we consider mobility time as an additional information point?
UPLC - IM - MS
2.28e4
8.20e3
Thiabendazole
Retention time (min)
692.4049
m/z
202.0466
m/z
202.0531
2.05 ms
14
4.45 min
10 ng/g of coriander
Retention time (min)
LC-MS
4.45 min
LC-IM-MS
+ IM Mobility time (ms)
a. Does IMS have the potential to separate target ions from matrix interferences?
15
b. Can we consider mobility time as an additional information point?
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
150.0000 350.0000 550.0000 750.0000
Tem
ps d
e m
obili
té (m
s)
m/z
Temps de mobilité du 2 marsTemps de mobilité du 9 mars
Mobility times are reproducible
2 March 2011
9 March 2011
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
150.0000 350.0000 550.0000 750.0000
Tem
ps d
e mob
ilité
(ms)
m/z
Temps de mobilité du 2 marsTemps de mobilité du 9 mars
Mob
ility
tim
e (m
s)
0
1
2
3
4
5
6
150.0 200.0 250.0 300.0 350.0
Mob
ility
tim
e (m
s)
m/z
Solvent
Lettuce
Strawberry
10ppb+60% matrice
Time4.00 4.25 4.50 4.75 5.00 5.25 5.50 5.75 6.00 6.25 6.50 6.75 7.00 7.25 7.50
%
0
100
4.00 4.25 4.50 4.75 5.00 5.25 5.50 5.75 6.00 6.25 6.50 6.75 7.00 7.25 7.50
%
0
100
4.00 4.25 4.50 4.75 5.00 5.25 5.50 5.75 6.00 6.25 6.50 6.75 7.00 7.25 7.50
%
0
100110521-Mix10A-fraise-04b_dt_01 Sm (Mn, 2x2) 1: TOF MS ES+
336.1014.74e3
5.74
110521-Mix10a-salade-05b_dt_705 Sm (Mn, 2x2) 1: TOF MS ES+ 336.093.10e4
5.74
110414-705-01 Sm (Mn, 2x2) 2: TOF MS ES+ 336.033_336.107
5.84e65.70
No matrix effect on mobility time
Fenamiphos sulfone
Solvent
16
b. Can we consider mobility time as an additional information point?
5.72 ms
Mobility time (ms)
17
To sum it up
ION MOBILITY is a powerful tool to
Ø Separate
q Compounds with the same mass
q Target ions from matrix interferences
Ø Identify
q mobility time could be considered as an additional IP
according to SANCO/10684 requirements
q UPLC IM MS should reduce the rate of false positive and
false negative samples
18
The best performance is obtain with Nitrogen
methamidophos m/z = 141.0013 dichlorvos
m/z = 219.9459
mepanipyrim m/z = 223.1109
spinosad m/z = 731.4608
19
Choice of separation gas
Drift time (ms)
20
21
Identification pesticides (Guidance criteria SANCO/10684)
