The multiresidue extraction was done following a modified QuEChERS method (Anastassiades
et al. 2003), where the samples are cut into pieces and macerated with a mixer grinder. A 15-g
macerated sample is then weighed into a 50-mL centrifuge tube along with 30 mL acetonitrile
and shaken well for 1 min in a vortex shaker. The supernatant is transferred quantitatively to a
second centrifuge tube containing 4 g anhydrous MgSO4 and 1 g NaCl. The tube was then
shaken vigorously again for 1 min in a vortex shaker and centrifuged at 3,000 rpm for 5 min. A8-
mL extract of this sample is added to a 15-mL centrifugetube that contains 1.2 g anhydrous
MgSO4 and0.4g primary secondary amine, shaken vigorously for 1 min in the vortex shaker, and
centrifuged at 3,000 rpm for 5 min. A 2-mL extract sample is pipette out into a glass tube and
the solvent is evaporated usinga Turbo Vap evaporator at 30 °C using 10 psi N2 gas over15 min.
The residues are reconstituted using n-hexanefor final GC and GC/MS analysis.
The detection and quantification of different pesticide compounds was carried out by injecting
1 μL of the extract into the gas chromatograph (GC-Shimadzu GC-2010) equipped with both an
electron capture detector and a flame thermionic detector. The residue levels were estimated
by comparing the peak areas of the samples to those of standards run under identical
conditions. Any detected residues were confirmed using GC/MS (GC/MS-TQD Brukers) to avoid
the misinterpretation of any results. Three vegetable samples with no residues were spiked
with 0.01 ppm levels of organochlorines, 0.05ppm for organophosphorus, and 0.1 ppm for
Synthaticpyrethroids compounds and separately analyzed following the same procedure. More
than 80 % recovery was obtained for the spiked samples and results were reported as such with
no correction for recovery rate. The average pesticide residue contents in the vegetable
samples were calculated using the equation given by Poulsen et al. (2007).