Selective enrichment of 17 pyrethroids from lyophilised agricultural samples

The screening of agricultural samples to determine 17 synthetic pyrethroids was investigated. Samples were lyophilised without losses of the insectici des, and then extracted with n-hexane. A simple, continuous preconcentratio n-elution system was developed, which included a silica sorbent column (pac ked with 50 mg) and used an air stream to carry the eluent (ethyl acetate) which minimised the eluate volume thus increasing the preconcentration fact or; so no evaporation step was required. Pyrethroids were determined by gas chromatography-electron capture detection (GC-ECD) by using a 5% phenylmet hylpolysiloxane-coated fused-silica capillary column; gas chromatography-ma ss spectrometry was used to identify the pyrethroids detected by GC-ECD mon itoring. Limits of detection varied between 0.1 and 0.8 ng/ml (except for p iperonyl butoxide, 25 ng/ml) with linear ranges from 1 to 200 ng/ml; the pr ecision of the method was high (3-6%). Recoveries of 17 insecticides from 1 4 different agricultural samples fortified at levels of 20-100 ng/g ranged from 66 to 102% (bifenthrin and deltamethrin were those providing the lowes t values, 66-87%). Pyrethroids were detected in eight samples (from the 100 unfortified agricultural samples tested) at concentrations lower than the established maximum residue limits (MRLs). (C) 2001 Elsevier Science B.V. A ll rights reserved.