SELECTIVE EXTRACTION OF PYRETHROID PESTICIDE-RESIDUES FROM MILK BY SOLID-MATRIX DISPERSION

A rapid procedure has been developed that allows a single-step, select ive extraction and clean-up of pyrethroid (PYR) pesticide residues fro m milk dispersed on solid-matrix diatomaceous material filled into dis posable cartridges and eluted by means of light petroleum saturated wi th acetonitrile and ethanol. The extract was cleaned up by high-perfor mance size-exclusion chromatography. Determinations were carried out b y gas chromatography with electron-capture detection. Recovery experim ents were carried out on homogenized commercial milk (3.6% fat content ) that was spiked with solutions of 14 PYR pesticides, viz., tefluthri n, tetramethrin, cyphenothrin, cyfluthrin, flucythrinate, fluvalinate, deltamethrin, bioallethrin, fenpropathrin, lambda-cyhalothrin, permet hrin, alpha-cypermethrin, esfenvalerate and tralomethrin, at levels ra nging from 0.04 to 0.41 mg/kg for the different PYR pesticides. Averag e recoveries were in the range 60-119% for the different PYR pesticide s, with relative standard deviations from ca. 2.5 to 14.4%. Coextracte d fatty material amounted to an average of ca. 5 mg/ml of milk. The so le extraction step requires about 30 min. The main advantages of the p rocedure are that extraction of PYR pesticides (with a minimum carry o ver of fat) is performed in a single step, emulsions do not occur, sev eral samples can be run in parallel by a single operator, reusable gla ssware is not needed and simple operations are required.