RAPID PRECONCENTRATION METHOD FOR THE DETERMINATION OF PYRETHROID INSECTICIDES IN VEGETABLE-OILS AND BUTTER FAT AND SIMULTANEOUS DETERMINATION BY GAS-CHROMATOGRAPHY ELECTRON-CAPTURE DETECTION AND GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

A simple and rapid solid-phase extraction (SPE)-GC method for the prec oncentration and quantification of pyrethroids at low nanogram levels in oils and high fat content samples is presented. The method was stud ied using seven highly persistent pyrethroid insecticides, viz.,cyperm ethrin, deltamethrin, fenvalerate, cyfluthrin, allethrin, cyhalothrin and permethrin. Preconcentration was achieved by treating the oil samp les with methyltrioctylammonium chloride and subsequent elution of the pyrethroid molecules from a graphitised carbon black SPE cartridge us ing 5 mi of acetonitrile. Pyrethroid quantification was achieved by GC with electron-capture detection. Recoveries of the pyrethroids at for tification levels of 0.05-0.5 ppm were 94-105%. Storage on graphitised carbon black for 30 d lowered the recovery of the pyrethroids by only 3-6%. The method compared well with results obtained by a GC-MS metho d. The relative standard deviation at a concentration level of 0.05-0. 2 mu g ml(-1) ranged from 1.31 to 5.16%. The limit of detection achiev ed was 0.002 mu g ml(-1) without any additional clean-up and with litt le interference from lipids during analysis.