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 chromatography (LC) using methanol only as mobile phase is described. Malathion [diethyl(dimethoxyphosphinothiol)succinate] was applied on marjoram, mint, and chamomile, Residues were detected in fresh and dry crops by LC and confirmed by gas-LC/mass spectrometry Average recovery of malathion was 85%, Residues detected in fresh marjoram, mint, and chamomile were 0.18, 0.23, and 0.083 mg/kg, respectively. Residues detected in dry marjoram and mint were 0.024 and 0.050 mg/kg, respectively. No malathion residues were detected in dry chamomile, The minimum detectable concentration with this method is 0.013 mg/kg, The study suggests it is safe to use malathion up to 2 sprays per season provided the crop is harvested not less than 3 weeks from the last spray.