Oxidation Pretreatment to Improve the Sensitivity of Acetylcholinesterase-Based Detection of Thioorganophosphates.

Bioassays based on the determination of acetylcholinesterase (AChE) activity are used for the detection and neurotoxicity evaluation of organophosphate insecticides. However, AChE bioassays are convenient for oxo and iso forms, whereas the limits of detection (LODs) of thio forms, being used as commercial insecticide preparations are significantly higher. In this study various malathion concentrations (1 × 10^–9–5 × 10^–4 mol/L) were treated with the oxidizing agent, N-bromosuccinimide (NBS) in concentration ratios: 1 : 1, 1 : 2, 1 : 10, and 1 : 20 to find efficient oxidation resulting in as possible as lower LODs of the used assays based on electric eel AChE (20 min-preincubation) and immobilized AChE incorporated in flow-injection analysis (FIA) system. Malathion–NBS ratio of 1 : 10 was found as the most efficient and resulted in a decrease of LOD about 100 times for both AChE bioassays. In the case of free AChE the obtained LOD values after the NBS-induced oxidation of thioorganophosphates (1 : 10), malathion, diazinon, and chlorpyrifos were as follows: 1.0 × 10^–8, 1.3 × 10^–8, and 1.0 × 10^–8 mol/L, respectively. In addition, LOD values for the FIA-AChE system involving a pre-step with NBS induced the following LOD values: 7.2 × 10^–7, 1.3 × 10^–6, and 1.8 × 10^–7 for malathion, diazinon, and chlorpyrifos, respectively. Furthermore, IC₅₀ values of the corresponding oxo forms were found to be similar to those for the studied thioorganophosphates, which indicates a potential stoichiometric conversion of the thio to oxo forms under the established oxidation conditions. [ABSTRACT FROM AUTHOR]