High Precision Pesticide Analysis in
Produce using GC Triple Quadrupole
and U-SRM Mode
Inge de Dobbeleer, Joachim Gummersbach, Hans-Joachim Huebschmann, Anton Mayer,
Thermo Fisher Scientific, Dreieich, Germany
Application Note 52279
Key Words
1 ppb Levels, Challenging Compounds, Pesticide Analysis, PTV Backflush,
U-SRM Mode, Selected Reaction Monitoring, Selectivity, Timed-SRM
Introduction
Pesticides are widely used in agriculture to protect crops
and to improve efficiency of production. Consequently,
governments, food producers and food retailers have the
duty to ensure that any residues occurring in foods for
human consumption are at or below Statutory Maximum
Residue Levels (MRLs). Regulation EC 396/2005 adopted
in the European Union sets MRLs for more than 500
different pesticides in over 300 different food commodities.
1
Many of these MRLs are set at a default value of
0.01 mg/kg, the typical limit of determination of routine
analytical methods. Thus, there is a requirement for food
safety laboratories to test a wide array of foods for a large
number of pesticide residues at concentrations at or below
0.01 mg/kg, with low costs and fast turnaround times
(often <48 hours). For the efficient control of the regulated
MRL levels, the overall method sensitivity in matrix is
required to be a factor of 10 lower. This is most often
achieved using multi-residue methods based on the use of
a combination of LC-MS/MS and GC-MS techniques to
determine pesticide residues in a single generic solvent
extract of the sample. One such example is the QuEChERS
(Quick, Easy, Cheap, Effective, Rugged and Safe) procedure,
which is based on acetonitrile extraction and dispersive
solid phase extraction.
2
After the QuEChERS extraction,
a solvent exchange was made to facilitate the GC injection.
The productivity benefit of using the QuEChERS extraction
technique is the fast turnaround time for a large number of
samples with small sample volumes in the range of 10 g.
Limitations of this approach are typically arising from
the heavy matrix load of QuEChERS extract requiring
increased robustness of the GC inlet system and increased
selectivity offered by using a MS/MS analyzer. This
application note describes the high quality and low level
analysis of pesticides in produce samples using the Thermo
Scientific TSQ Quantum XLS Ultra GC-MS/MS system.
For most of the pesticide compounds included in the
method, the complete list of the compounds with their
respective SRM transitions have been downloaded from
the Pesticides Method Reference CD (provided with the
manual p/n 120390) into the instrument acquisition method.
Each transition has been determined for optimal sensitivity
and selectivity, with the complete list documented for
TSQ Quantum XLS users.
Over 400 pesticides have been monitored in several
matrices such as wheat, blackcurrants and cucumber;
the results of the most challenging pesticides in terms of
activity and response are highlighted, showing calibration
curves, repeatability and ion ratio stabilities.
The TSQ Quantum XLS Ultra
™
is able to perform SRM
with a higher mass resolution (0.1 Da) setting thus allowing
for better selectivity. Not all pesticides in all matrices
benefit from a higher mass resolution setting, but depending
on the matrix and the compound analyzed, there can be
a significant improvement on the signal to noise ratio.
Some examples are shown in the ‘Advanced GC-MS/MS
Experiment’ section of this application note.
