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Comparing LC and GC Triple Quadrupole MS for the Screening of 500 Pesticides in Matrix
Overview
Purpose:
The goal of this project is to compare the screening of more than 500
pesticides in matrix by LC and GC triple quadrupole, and determine the value of a
comprehensive LC and GC screening approach.
Methods:
The methodology included the vegetable extraction by QuEChERS
followed by GC-MS/MS and LC-MS/MS analysis of over 500 pesticides in matrix.
Results:
The majority of compounds could be detected to levels acceptable by EU
standards by either GC/MS or LC/MS. All but eight pesticides could be determined to
acceptable levels by the combined GC/LC methodology.
Introduction
Modern pesticide analysis is extremely challenging due to the diversity of compounds
required to be reported, especially in the area of food safety control. Furthermore,
the pressure to report large numbers of pesticides quickly makes it attractive to use
large single injection methods. Triple quadrupole mass spectrometry has emerged as
a primary technique for screening large target lists of pesticides due to its high
sensitivity and selectivity against matrix. However, because of the chemical diversity
of pesticides, LC or GC introduction alone may not be ideal, or even sufficient for a
comprehensive analysis. Presented is a comparison of both LC and GC sample
introduction techniques coupled to triple quadrupole mass spectrometer for the
screening of more than 500 pesticides at ppb levels.
Methods
Sample Preparation
Pesticide standards were obtained from the U.S. Food and Drug Administration
(FDA). In order to determine detection limits of such a wide range of pesticides,
standards were prepared at multiple levels, enabling the selection of an appropriate
level to determine the detection limit of each compound.
.
Vegetable matrices were prepared for analysis by using a modified QuEChERS
(Quick, Easy, Cheap, Effective, Rugged, and Safe) method, which is a sample
preparation procedure used to extract pesticides from food
1
. The QuEChERS extracts
were obtained from California Department of Food and Agriculture. For the
QuEChERS extraction, 15 g of homogenized sample and 15 mL of acetonitrile were
used.
GC/MS Instrument Methodology
Gas Chromatograph Method Conditions
A method was developed for the Thermo Scientific™ TRACE™ 1310 Gas
Chromatograph and Thermo Scientific™ TSQ™ 8000 Mass Spectrometer. A
Programmable Temperature Vaporization (PTV) injector was used on the TRACE
1310. The ability to program a temperature ramp with this injector was utilized so that
thermally labile pesticides would be transferred to the analytical column at as low a
temperature possible.
Similarly, the oven on the TRACE 1310 gas chromatograph was ramped, volatilizing
pesticides on the column as their boiling points were reached. A slow ramp of 5 ºC/min
was employed between an oven temperature of 180 ºC and 280 ºC, which is the
range in which the majority of these pesticides are volatilized, to achieve optimal
separation during this most dense part of the chromatogram. Figure 1 shows the total
ion chromatogram resulting from the GC/MS method, and Figure 2 lists the GC
method parameters.
FIGURE 2. Gas Chro
FIGURE 3. GC-Mass
GC-Triple Quadrupol
Transitions for all pes
Pesticide Analyzer. T
AutoSRM software, w
energies optimized to
acquisition and proce
compounds from the
list in the instrument
Thermo Scientific™ T
compound was used
confirmation. Figure
FIGURE 1. GC/MS Total Ion Chromatogram.
The analytical column
with dimensions 30 m
Siltek™ deactivated i
