RAPID-DETERMINATION OF METHYL PARATHION AND METHYL PARAOXON IN MILK BY GAS-CHROMATOGRAPHY WITH SOLID-PHASE EXTRACTION AND FLAME PHOTOMETRICDETECTION

Methyl parathion (MPT; O,O-dimethyl-O-4-nitrophenyl phosphorothioate) and its active metabolite, methyl paraoxon (MPO; O,O-dimethyl-O-4-nitr ophenyl phosphate), were isolated from raw milk by solid-phase extract ion (SPE) and determined by gas chromatography with flame photometric detection, The SPE method was compared with a traditional liquid-liqui d extraction (LLE) procedure to determine whether SPE had suitable sen sitivity and better efficiency in extracting MPT and MPO from milk of cows and goats, Method detection limits were higher for SPE, but the d ifferences were not significant (t-test), Recoveries of MPT and MPO fr om raw milk samples spiked at 0.05, 0.5, and 5.0 mu g/mL ranged from 8 0.0 to 118%, and the coefficients of variation were usually less than 10% for both methods, LLE required more organic solvents and was more time consuming compared with SPE.