2
Broad Scope Pesticide Screening in Food Using Triple Quadrupole GC-MS
Overview
Purpose:
To demonstrate two different ways to perform targeted and non-targeted
screening of pesticides in one analytical run
Methods:
Screening for 600 pesticides in selected reaction monitoring (SRM) mode or
a smaller subset in selected reaction monitoring/ full scan (SRM/FS) mode
Results:
Either method can be used to analyze targeted and non-targeted compounds
with little loss of sensitivity
Introduction
The increased accessibility of high selectivity GC-MS has enabled more generic
sample preparation in pesticide testing, allowing consolidation of multiple analyte lists
and matrices into one method. GC-MS/MS is well suited to multi-residue analysis in a
diverse range of matrices. However, as the number of targeted compounds increases,
the complexity of method optimization increases and analytical performance becomes
compromised. Furthermore, there is a desire to look beyond targeted lists for other
potentially harmful food contaminants. Presented here is the use of smart instrument
control and data processing software applied to GC-MS/MS analysis of 600 pesticides
in matrix to mitigate analytical performance degradation through MS duty cycle
optimization. Also discussed is the combining of this optimized targeted quantitation
with general unknown analysis through full scan/SRM.
Method 1 – Screening For 600 Pesticides
Sample Preparation
Lettuce was purchased from a local grocery store and was extracted with 1:1 ethyl
acetate/cyclohexane following the QuEChERS method of extraction and clean-up, then
5 mL of solvent exchanged into 1 mL of hexane:acetone (9:1). The concentrated
extract was spiked with various mixes of calibration standards.
Gas Chromatography
The Thermo Scientific™ TRACE™ 1310 GC was equipped with both an SSL and PTV
inlet. A 1 µL injection was performed on the PTV inlet. The liner was a Siltek™
deactivated baffled liner (Thermo Scientific part number 453T2120). Chromatographic
separation was achieved by using a 5% diphenyl/95 % dimethyl polysiloxane column
(30 m x 0.25 mm 0.25 µm). See Table 1 for the parameters for the PTV and oven.
TABLE 1. PTV and Oven Parameters.
Results
Quantitative performanc
screening for all 600 pe
Curves were generated
replicates of a 40 ppb m
capability, a few additio
been part of the calibrati
The average concentrat
Figure 5 shows the qua
ppb spiked sample that
the ability of the method
samples for which the in
TABLE 2. 40 ppb Stan
Mass Spectrometry
The targeted screenin
Thermo Scientific™ T
determined in full scan
(SRM) was constructe
transitions were entere
Compound Database.
instrument method thr
was set to 250 C, and
SRM (t-SRM) which all
good sensitivity.
FIGURE 1. Small Sect
Compound Name
Acibenzolar-S-methyl
Azinphos-methyl
Azoxystrobin
Benalaxyl
Bendiocarb
Bitertanol
Boscalid (Nicobifen)
Buprofezin
Carbaryl
Carbofuran
Carboxin
Carfentrazon-ethyl
Clethodim
Cyprodinil
Diethofencarb
Difenoconazole peak 1
Difenoconazole peak 2
Dimethomorph-1
Dimethomorph-2
Ethofumesate
Fenamidone
Fenbuconazol
Fenoxycarb
Flonicamid
Fludioxonil
Flusilazole
PTV
Mode
Temp
Split
Flow Splitless Time Purge Flow
Splitless
75
50
2.00
5.00
Flow Ramps
Rate
Flow Hold
(mL/min)
(ml/min)
(min)
1.2
30
2
3
7.2
Injection phases Pressure Rate
Temp
Time
Flow
(kPa)
(°C/sec)
(°C)
(min)
(mL/min)
Injection
70
0.1
50
Transfer
210
2.5
300
3.00
Cleaning
14.5
330
20
75
Oven Program Ramp
Rate
Temp Hold Time
(°C/min)
(°C)
(min)
Initial
90
5
1
25
180
0
2
5
280
0
3
10
300
5
