GC Determination of Residual Amounts of Organophosphorus and Pyrethroid Pesticides in Wheat Flour

Gas chromatography was applied to the determination of residual amounts of organophosphorus and pyrethroid pesticides, i.e., phorate, chlorpyrifos, fenpropathrin and deltamethrin, in wheat flour. The pesticides were separated from wheat flour sample by extraction with acetonitrile and the extract was evaporated to near dryness under reduced pressure and then to dryness by N2-blowing. Two mL of mixed solvent of n-hexane and ethylacetate (9+1) were used to take up the residue and the solution was purified by passing through SPE column of neutral aluminum oxide. The eluate (together with the 10 mL of the same mixed solvent used as eluant to wash the column) was collected and evaporated to dryness by N2-blowing. The residue was taken up with 1.0 mL of n-hexane, which was used for GC analysis. HP-5 chromatographic column, electron capture detector and external standard method were used in the determination. Linearity ranges for the 4 presticides were found to be same between 50-1 000 μg·L-1, with same lower limit of determination (10S/N) of 10 μg·kg-1. Recovery was tested at 3 different concentration levels and values of recovery found were ranged from 85.4% to 95.9% with RSD′s (n=5) in the range from 2.6% to 5.5%.