Non-enzymatic electrochemical detection of paraoxon ethyl by differential pulse voltammetry using a disposable graphite pencil electrode

This work exhibits a nonenzymatic, sensitive, and simple electrochemical determination of paraoxon ethyl (PO-Et) at a bare graphite pencil electrode (GPE), which has several advantages, such as disposability, commercial availability, cost-effectiveness, and no requirement for long-time polishing and preparation steps. Cyclic voltammetric results show that the electroactive aromatic nitro group (Ar-NO2) in the structure of PO-Et is irreversibly reduced to N-hydroxyl amine (Ar-NHOH) by accepting 4e-and 4H+ at-700 mV vs. Ag/AgCl(sat. KCl) in a pH 10.0 Britton Robinson buffer (BRB) solution containing 0.10 M KCl. After that, the produced Ar-NHOH is reversibly oxidized to a nitroso group (Ar-N=O) by giving 2e-and 2H+ at a formal potential of-225 mV. The differential pulse voltammetric method has been proposed for sensitive and selective determination of PO-Et by evaluation of both irreversible nitro group reduction (RedI) and reversible N-hidroxyl amine group oxidation (OxII)/nitroso group reduction (RedII) of PO-Et for the first time. Two linear calibration curves for each peak were obtained with a detection limit of 17.0, 8.0, and 9.0 nM for OxII, RedII, and RedI, respectively. The application of the proposed voltammetric method has been performed in the three different real samples, such as water, soil, and tomato juice, and recovery results close to 100 % demonstrate an acceptable accuracy of the method. In addition, the PO-Et levels in the spiked real samples were determined with a standard spectrophotometric method, and the results have found a good agreement between the proposed electrochemical and standard UV-Vis spectrophotometric methods.