GC Determination of Residual Amounts of Pyrethroid Pesticides in Vegetables

Edible parts of 1.0 kg of vegetable were taken,cut up and sampled by quartering.An appropriate amount of the sample was pounded thoroughly to prepare the sample for analysis.25.00 g of the sample was extracted with 50 mL of acetonitrile for 3-5 min by high speed homogenization,and 40-50 mL of the filtrate was salted out by shaking with 5 g of NaCl.An aliquot of 10 mL of the supernatant was taken and blown to dryness with nitrogen at 80℃over a water-bath.The residue was taken up with 2 mL of n-hexane.which was purified on Florisil column.The column was eluted twice with 5 mL of mixed solvent of acetone-n-hexane(1+9),and the eluates were combined and blown to dryness by nitrogen at 50℃on a water bath.The residue was taken up with 2.0 mL of n-hexane,and 1μL was taken from it for GC analysis using Varian CP-Sil 5CB capillary column for separation and ECD for determination.Five pyrethroid pesticides were satisfactorily separated under this condition. Linearity ranges between values of peak area and mass concentration of the pesticides were found same between 0.01 and 1.0 mg·L~(-1),with detection limits(3S/N) in the range of 1.6-2.0μg·kg~(-1).Recovery and precision were tested by standard addition method at 3 concentration levels(0.02,0.01,0.50 mg·kg~(-1)),giving results of recovery in the range of 90.5%-106.4%and RSD's(n = 6) ranged from 0.98%to 6.3%.