Semiautomatic multiresidue gas chromatographic method for the screening of vegetables for 25 organochlorine and pyrethroid pesticides

A method for multiresidue screening of lyophilised vegetables for up to 25 pesticides (16 pyrethroids and 9 OCPs) permitted in the European Union was systematically developed on the basis of solid-phase extraction and gas chromatography with electron capture detection. The residues of pesticides were extracted from the lyophilised sample with n-hexane by mechanical shaking; the organic phase containing the pesticides was aspirated into a continuous module which comprises a laboratory-made silica column for analyte preconcentration and sample matrix clean-up. The method provides excellent clean-up despite the complexity of the matrices involved thanks to the lyophilisation process which also helps to sample preservation without losses of the selected relatively non volatile analytes. Detection limits were about 1-10ng/g, except for lindane and captan (30ng/g) thus allowing their determination at concentrations lower than their maximum residue limits with good precision (ca. 5%). The accuracy of the quantitative determination measured in terms of average percentage recovery of the 25 compounds in eight different vegetables was 93±3, bifenthrin and deltamethrin excepted. The proposed method was applied to the screening of about 100 vegetables for the selected pesticides, being the positive findings further confirmed by GC/MS.