RAPID CLEANUP OF FAT EXTRACTS FOR ORGANOPHOSPHORUS PESTICIDE-RESIDUE DETERMINATION USING C-18 SOLID-PHASE EXTRACTION CARTRIDGES

Commercial solid-phase extraction (SPE) cartridges with C18 bonded silica packings effectively cleaned up acetonitrile extracts of 3-g samples of fats and oils for determination of organophosphorus pesticide residues by gas chromatography with flame photometric detection. Cartridges from three different sources were tested and found to differ in lipid capacity and inertness (free silanol activity). Consequently, the amount of packing (i.e., number of cartridges) and/or the choice of eluent used were adjusted for each brand of cartridge to achieve optimum clean-up and analyte recovery. Seven pesticides with a wide range of polarity (acephate, azodrin, chlorpyrifos, diazinon, malathion, methamidophos and methyl parathion) were separated from coextracted lipids by elution with either acetonitrile or methanol, depending on the brand of cartridge used. Cartridges were regenerated by purging lipids with dichloromethane and were reused numerous times without apparent loss of effectiveness. Recoveries from vegetable oils and butterfat fortified with the seven compounds at levels of 0.05-0.87-mu-g g-1 ranged from 80 to 103%. Practical limits of determination range from 0.01 to 0.08-mu-g g-1, depending on analyte response.