Spectrophotometric determination of parathion and paraoxon using alkaline hydroxylamine solution for the liberation of 4-nitrophenol

Abstract

The half-time for the liberation of 4-nitrophenol from parathion (diethyl 4-nitrophenyl phosphorothionate) at 20 °C in the presence of 0.5 M sodium hydroxide solution is several hours, but this time can be reduced nearly a 1000-fold when the alkali is replaced with a mixture of 0.5 M sodium hydroxide solution and 0.67 M hydroxylamine solution. The reaction is almost instantaneous when the system also contains 33% of ethanol. A procedure is described, based on these findings, for the spectrophotometric determination of parathion and paraoxon via the 4-nitrophenol liberated. The method is simple and quantitative and does not involve the use of drastic chemical procedures such as those required for methods that are currently available. The sensitivity of the method is about 0.1 µmol of parathion. Mixtures of parathion and paraoxon can be determined by using a selective extraction procedure.