Detection of coumaphos in honey using a screening method based on an electrochemical acetylcholinesterase bioassay

An analytical protocol based on an electrochemical assay for the detection of acetylcholinesterase (AChE) inhibitors has been optimised for the detection of coumaphos in honey. Coumaphos is a phosphotionate insecticide requiring transformation in the corresponding oxo-form to act as an effective AChE inhibitor. The inhibition assay was based on the electrochemical detection of the product of AChE, choline, via a choline oxidase biosensors obtained using prussian-blue modified screen printed electrodes. A simple procedure for the oxidation of coumaphos via N-bromosuccinimide (NBS) and AChE inhibition was optimised. A calibration curve for coumaphos (8-1000 ng/ml) was obtained in buffer; the intra electrode CV ranged between 8 and 12% whereas the inter electrode CV was comprised between 12 and 14%. A detection limit (LOD) of 8 ng/ml was achieved, with an I(50%) of 105 ng/ml. The assay was then applied to detect coumaphos in honey samples. Despite the solubility of the samples in buffer, the assay was affected by many electrochemical interferences present in this sample matrix A simple C18 based solid phase extraction procedure has been then optimised and used for the assay. This allowed to eliminate all the electrochemical interferences with a satisfactory coumaphos recovery (around 86%) for a final LOD of 33 ng/g. The developed assay applied to detect coumaphos in different honey samples gave data well correlated with LC-MS detection.