Simultaneous determination of malathion, permethrin, DEET (N,N-diethyl-m-toluamide), and their metabolites in rat plasma and urine using high performance liquid chromatography

A method was developed for the separation and quantification of the insecticide malathion (O,O-dimethyl-S-(1,2-carbethoxyethyl) phosphorodithioate). its metabolite malaoxon (O,O-dimethyl-S-(1,2-carbethoxyethyl) phosphorothioate), the insecticide permethrin (3-(2,2-dichloro-ethenyl)-2,2-dimethylcyclopropanecarboxylic acid(3-phenoxyphenyl)methylester), two of its metabolites m-phenoxybenzyl alcohol and m-phenoxybenzoic acid, the insect repellent N,N-diethyl-m-toluamide (DEET), and its metabolites m-toluamide and in-toluic acid in rat plasma and urine. The method used high performance liquid chromatography (HPLC) with reversed phase C-18 column, and UV detection at 210 nm. The compounds were separated using gradient of 45-99% acetonitrile in water (pH 3.5) at a flow rate ranging between 0.5 and 2 ml/min in a period of 15 min. The retention times ranged from 7.4 to 12.3 min. The limits of detection ranged between 20 and 100 ng/ml, while limits of quantitation were 50-150 ng/ml. Average percentage recovery of five spiked plasma samples were 80.1 +/- 4.2, 75.2 +/- 4.6, 84.5 +/- 4.0, 84.3 +/- 3.4, 82.8 +/- 3.9, 83.9 +/- 5.5, 82.2 +/- 6.0, 83.1 +/- 4.3, and from urine 78.8 +/- 3.9, 76.4 +/- 4.9, 82.3 +/- 4.5, 82.5 +/- 3.9, 81.4 +/- 4.0, 83.9 +/- 4.3, 81.5 +/- 5.0, and 84.5 +/- 3.8 for, malathion, malaoxon, DEET, m-toluamide, ni-toluic acid, permethrin, m-phenoxybenzyl alcohol, and m-phenoxybenzoic acid, respectively. The method was reproducible and linear over range between 100 and 1000 ng/ml. This method was applied to analyze the above chemicals and metabolites following combined dermal administration in rats. (C) 2001 Elsevier Science B.V. All rights reserved.