Indirect electrochemical oxidation of organophosphorous pesticides for efficient detection via acetylcholinesterase test

Abstract

Organothiophosphorous pesticides diazinon, malathion, chlorpyrifos, azinphos-methyl and phorate, have been indirectly electrochemically oxidized in aqueous media using anodically evolved Cl2, Br2 or I2 as a pre-step for their detection via acetylcholinesterase-based test. The presence of single oxidation product, corresponding oxo-form, was confirmed by UPLC analysis, as well as its stability with respect to hydrolysis. Comparing different halogens, the best results were obtained using Br2 as the oxidant due to high reactivity of HOBr, which is formed upon chemical reaction of anodically formed Br2 with water. Limits of detection of five analyzed pesticides were lowered upon indirect electrochemical oxidation with Br2 for two orders of magnitude or more, comparing to unoxidized parental thio-forms. In fact, the lowest possible detection limits for all five pesticides using proposed analytical procedure were achieved, as being determined by detection limits of corresponding oxo forms. Comparison of here proposed electrochemical oxidation pre-step with earlier reported ones is provided and discussed. © 2012 Elsevier Inc.