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

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Abstract
A simple and rapid solid-phase extraction (SPE)–GC method for the preconcentration and quantification of pyrethroids at low nanogram levels in oils and high fat content samples is presented. The method was studied using seven highly persistent pyrethroid insecticides, viz., cypermethrin, deltamethrin, fenvalerate, cyfluthrin, allethrin, cyhalothrin and permethrin. Preconcentration was achieved by treating the oil samples with methyltrioctylammonium chloride and subsequent elution of the pyrethroid molecules from a graphitised carbon black SPE cartridge using 5 ml of acetonitrile. Pyrethroid quantification was achieved by GC with electron capture detection. Recoveries of the pyrethroids at fortification 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 method. The relative standard deviation at a concentration level of 0.05–0.2 µg ml–1 ranged from 1.31 to 5.16%. The limit of detection achieved was 0.002 µg ml–1 without any additional clean-up and with little interference from lipids during analysis.

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