Thin layer chromatographic determination of methyl parathion as paraoxon by cholinesterase inhibition

A simple, sensitive, and rapid method is described for the quantitative estimation of nanogram amounts of methyl parathion (O, O-dimethyl O-p-nitrophenyl phosphorothioate) as methyl paraoxon (O,O-dimethyl O-p-nitrophenyl phosphate) on thin layer chromatograms. Methyl paraoxon is detected by pig liver acetone powder cholinesterase inhibition, using p-nitrobenzenediazoniumfluoroborate as the chromogenic reagent. Commercial pig liver acetone powder is more advantageous than raw liver sources because it is readily available and can be preserved indefinitely. About 0.1 ng methyl parathion can be detected, and amounts from 5 to 50 ng can be quantitatively estimated.