SIMPLE AND RAPID SYSTEMATIC DETERMINATION OF VARIOUS PESTICIDES IN BROWN RICE BY GAS-CHROMATOGRAPHY

A simple and rapid systematic gas chromatographic determination of 43 organophosphorus, 24 organonitrogen, 14 organochlorine, and 11 pyrethroid pesticides in brown rice was developed. The pesticides were extracted from samples with acetonitrile, and this extract was evaporated to dryness. The residue was dissolved in acetone, and organophoshorus pesticides were directly determined by FPD-GC. Another part of the solvent was applied to a Sep-pak Florisil cartridge, and organonitrogen pesticides were eluted with 50% ethyl acetate in n-hexane and determined by NPD-GC. On the other hand, organochlorine and pyrethroid pesticides were eluted with 5% ethyl acetate in n-hexane and determined by ECD-GC. This simple method affords a high recovery of hydrophilic pesticides, allows rapid analysis, and is cheap to perform. Residual pesticides in brown rice (246 samples) imported from the U.S.A., China and Australia were investigated by the proposed method, and 0.01 similar to 0.1 ppm of malathion was found in 3 samples from the U.S.A., and 6 samples from China. The detection limit of the proposed method was 0.001 ppm for organophosphorus and organochlorine pesticides and 0.01 ppm for organonitrogen and pyrethroid pesticides.