Oxidation as a Pre-Step in Determination of Organophosphorus Compounds by the AChE-Tls Bioassay

Laboratory for Environmental Research, Nova Gorica Polytechnic, Vipavska 13, P. O. Box 301, 5001-SI,
Nova Gorica, Slovenia

Abstract
The oxidation efficiency of N-bromosuccinimide (NBS), hypochloride and other oxidants such as m-CPBA, Oxone, CAN, iodine water, hydrogen peroxide in aqueous solution and juice samples spiked with four model thio-organophosphorus compounds (thio-OPs): azinphos-methyl, chlorpyrifos, diazinon and malathion, was studied. The complete conversion into oxons was noticed within five minutes in case of NBS, a partial conversion in case of sodium hypochlorite, and no oxo-products were observed using other oxidants. Since the NBS is efficient in acidic conditions and hypochlorite in alkaline media, the hydrolysis during the oxidation process can be significantly avoided using appropriate pHs. All oxidation experiments were verified using GC-MS analysis. Compounds of interest were quantified by using standard solutions of thio-OPs and identification of formed oxo-OPs was based on MS spectra. The formed oxo-analogs were detected using AChE-bioassay with TLS detection, which enabled determination of parent thio-compounds at ppb levels. With a rapid (5 min) oxidizing pre-step the AChE-bioassay can serve as a fast pre-screening test (15 min) to identify samples that contain AChE inhibitors, including the thio-OPs.

Key words: organophosphorus pesticides, oxidation, AChE-TLS bioassay