Selective extraction of pyrethroid pesticide residues from milk by solid-matrix dispersion

A rapid procedure has been developed that allows a single-step, selective extraction and clean-up of pyrethroid (PYR) pesticide residues from milk dispersed on solid-matrix diatomaceous material filled into disposable cartridges and eluted by means of light petroleum saturated with acetonitrile and ethanol. The extract was cleaned up by high-performance size-exclusion chromatography. Determinations were carried out by gas chromatography with electron-capture detection. Recovery experiments were carried out on homogenized commercial milk (3.6% fat content) that was spiked with solutions of 14 PYR pesticides, viz., tefluthrin, tetramethrin, cyphenothrin, cyfluthrin, flucythrinate, fluvalinate, deltamethrin, bioallethrin, fenpropathrin, lambda-cyhalothrin, permethrin, alpha-cypermethrin, esfenvalerate and tralomethrin, at levels ranging from 0.04 to 0.41 mg/kg for the different PYR pesticides. Average recoveries were in the range 60-119% for the different PYR pesticides, with relative standard deviations from ca. 2.5 to 14.4%. Coextracted fatty material amounted to an average of ca. 5 mg/ml of milk. The sole extraction step requires about 30 min. The main advantages of the procedure are that extraction of PYR pesticides (with a minimum carry over of fat) is performed in a single step, emulsions do not occur, several samples can be run in parallel by a single operator, reusable glassware is not needed and simple operations are required.