DETERMINATION OF MALATHION RESIDUES IN SOME MEDICINAL-PLANTS BY LIQUID-CHROMATOGRAPHY WITH GAS-CHROMATOGRAPHIC MASS-SPECTROMETRIC CONFIRMATION

A method for determining malathion residues by reversed-phase liquid c hromatography (LC) using methanol only as mobile phase is described. M alathion [diethyl(dimethoxyphosphinothiol)succinate] was applied on ma rjoram, mint, and chamomile, Residues were detected in fresh and dry c rops by LC and confirmed by gas-LC/mass spectrometry Average recovery of malathion was 85%, Residues detected in fresh marjoram, mint, and c hamomile were 0.18, 0.23, and 0.083 mg/kg, respectively. Residues dete cted in dry marjoram and mint were 0.024 and 0.050 mg/kg, respectively . No malathion residues were detected in dry chamomile, The minimum de tectable concentration with this method is 0.013 mg/kg, The study sugg ests it is safe to use malathion up to 2 sprays per season provided th e crop is harvested not less than 3 weeks from the last spray.