AI10382-GC-MS-Food Safety-Analysis - page 10

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injected via autosampler for analysis. For recovery and
validation studies 15 g of the "churna" was fortified with
appropriate quantities of the pesticide standard mixture.
Calibration
Stock standard solutions of each pesticide compound
were prepared by weighing 10±0.1 mg, dissolving in
10 mL acetonitrile and storing the solution in amber-
colored glass vials at -20℃ . A total of ten intermediate
mixtures (each containing 15-20 compounds) of 10 mg/L
concentration were prepared by diluting an adequate
quantity of each compound in acetonitrile. A working
standard solution (1 mg/L) was prepared by mixing an
adequate quantity of intermediate standard solution
and dilution with acetonitrile and storing the solution at
-20℃ . The calibration standards at 2.5, 5, 10, 25 and
50 µg/L were freshly prepared for measurement of the
calibration curves. The calibration graphs (five points)
for all the compounds were obtained by plotting the
individual peak areas against the concentration of the
corresponding calibration standards.
Instrument and Method Setup
The analytical method comprises the sample handling
using the Thermo ScientificTM TriPlusTM RSH liquid
auto sampler, the Thermo ScientificTM TRACETM 1300
Series gas chromatograph equipped with a temperature
programmable PTV injector, and the Thermo ScientificTM
TSQ 8000TM triple quadrupole GC-MS/MS system. The
instrument method parameters are summarized in Table 1.
The Thermo ScientificTM TraceFinderTM software
was used for method setup and data processing. The
TraceFinder software provides a compound database of
pesticides compoundsof more than 800 compounds with
all required analytical details such as retention times and
the optimized SRM transitions for data acquisition and
processing. These software features were employed to
create the processing method for the screening a large
pesticides compound list [2].
For all pesticide compounds two SRM transitions were
chosen for the overall MRM acquisition method. The
first transition was used for quantitation, the second
transition for confirmation by checking the ion intensity
ratio by the TraceFinder software during data processing.
Retention times had been synchronized between data
processing of standards with the acquisition method for
the timed-SRM protocol (see Figure 2) in order to lock
all compound retention times for robustness independent
on the impact of the matrix carried by real life sample.
TABLE 1. Instrument method parameters.
TRACETM 1310 Gas Chromatograph Parameters
Carrier gas Helium
Injector PTV
Mode splitless
Splitless time 3 min, split flow: 30 mL/min
PTV program 87 ℃ , 0.3 min (injection)
14.5 ℃/min to 285 ℃ (transfer)
285 ℃ , 2.5 min (transfer)
14.5 ℃/min to 290 ℃ (cleaning)
290 ℃ , 20 min (cleaning)
Column Thermo Scientific TraceGOLDTM
TG-5 SilMS, 30 m x 0.25 mm x
0.25 µm (p/n 10177894)
Column flow 1.2 mL/min, constant flow
Oven program 70 ℃ , 2 min
10 ℃/min to 200 ℃
200 ℃ , 1 min
10 ℃/min to 28 ℃
285 ℃ , 8.5 min
Injection 3 µL by TriPlus RSH Autosampler
TSQ-8000 MS/MS Parameters
Ion source temperature 230 ℃
Interface temperature 285 ℃
Acquisition mode EI, 70 eV
MRM detection Timed SRM mode (see Figure 1)
Acquisition rate 500 ms
MRM parameter See Table 1
The timed-SRMacquisition method used with the TSQ 8000
MS avoids the laborious and time-consuming process of
segment creation and method maintenance.The scan times
are automatically calculated based upon the specified
cycle time so that uniform cycle times are obtained
for each mass transition, thus reducing the extensive
optimization process for scan times and data points
across a peak. The dwell times for data acquisition are
maximized independently for the number of compounds
in the MRM method. Table 2 lists the MRM parameters
for the compounds analyzed in this method.
The data processing and reporting was done using the
quantitation and reporting suite. The software allows
retention time locking by synchronization between
the data processing and the acquisition setup for all
compounds in the method.