Colorimetric determination of methyl parathion and oxygen analog

A simple, sensitive, and rapid colorimetric method is described for determining methyl parathion (O,O-dimethyl-O-p-nitrophenyl phosphorothioate) and methyl paraoxon (O,O-dimethyl-O-p-nitrophenyl phosphate), using p-nitrobenzene diazonium fluoroborate as the chromogenic salt. This colorimetric method is more sensitive than are other colorimetric methods based on non-enzymatic reactions. Pig liver acetone powder cholinesterase was found to be sensitive to methyl parathion. Inhibition can be detected at picogram levels, and 50-80 ng methyl paraoxon and 1-9 micrograms methyl parathion can be estimated.