Abstract

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.

中文翻译：

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氧化预处理提高基于乙酰胆碱酯酶的硫代有机磷酸盐检测的灵敏度

摘要

基于乙酰胆碱酯酶 (AChE) 活性测定的生物测定用于有机磷杀虫剂的检测和神经毒性评估。然而，AChE 生物测定法适用于氧代和异构体，而用作商业杀虫剂制剂的硫代形式的检测限 (LOD) 则明显更高。在本研究中，使用氧化剂N-溴代琥珀酰亚胺 (NBS) 处理不同浓度的马拉硫磷 (1 × 10 ^–9 –5 × 10 ^–4 mol/L )，浓度比为：1 : 1、1 : 2、1 : 10和 1:20，以找到有效的氧化，从而使基于电鳗 AChE（预孵育 20 分钟）和流动注射分析 (FIA) 系统中的固定化 AChE 的所用测定的 LOD 尽可能低。马拉硫磷与 NBS 的比例为 1:10 被发现是最有效的，并且导致两种 AChE 生物测定的 LOD 降低约 100 倍。对于游离乙酰胆碱酯酶，硫代有机磷酸酯 (1:10)、马拉硫磷、二嗪农和毒死蜱经 NBS 诱导氧化后获得的 LOD 值如下：1.0 × 10 ^–8、1.3 × 10 ^–8和 1.0 × 10分别为^–8 mol/L。此外，涉及 NBS 预处理的 FIA-AChE 系统的 LOD 值得出以下 LOD 值：马拉硫磷、二嗪磷和毒死蜱为7.2 × 10 ^–7、1.3 × 10 ^–6和 1.8 × 10 ^–7 。分别。此外，发现相应的氧代形式的IC ₅₀值与所研究的硫代有机磷酸酯的IC 50 值相似，这表明在既定的氧化条件下，硫代化合物可能以化学计量转化为氧代形式。