BACKGROUND: Thiamethoxam (3-[(2-chloro-5-thiazolyl)methyl]tetrahydro-5-methyl-N-nitro-4H-1,3,5-oxadiazin-4-imine) belongs to a relatively new class of insecticides known as neonicotinoids, which can block irreversibly nicotinic acetylcholine receptors of the nervous system of insects. Its determination at trace levels is an acute analytical problem. Therefore, chromatography, spectroscopy, and electrochemical technics were reported. These last have several advantages (simple sensitive and less expensive). This work investigated the electro-reduction of Thiamethoxam using simple and rapid method in real samples using metallic silver electrode. RESULTS: Silver particles, known as effective catalysts in the reduction of nitro groups, were studied to explore their roles in the shift of thiamethoxam peak potential. Cyclic voltammetry, Tafel plot and electrochemical impedance spectroscopy analysis suggest that metallic silver electrodes have a significantly greater electrocatalytic activity in thiamethoxam electroreduction than glassy carbon electrodes and carbon paste electrodes. The electrocatalytic activity of metallic silver electrodes in thiamethoxam reduction was investigated by cyclic voltammetry and chronoamperometry. A linear variation in cathodic current with the square root of the scan rate was observed, suggesting that the process is diffusion controlled. Several supporting electrolytes were tested, and the best results were obtained with Britton-Robinson (BR) buffer, pH 10.4. A linear relationship between peak current and concentration was found in the range from 1.0 × 10 −5 to 1.0 × 10 −4 mol L −1 using square wave voltammetry (SWV) with a correlation coefficient of 0.994. The detection limit and quantification limit were 5.49 × 10 −6 and 1.83 × 10 −5 mol L −1 , respectively. CONCLUSION: Silve metallic electrode exhibits efficient catalytic activity towards the Thiamethoxam reduction. The proposed electrode was then used for the determination of thiamethoxam in tomato anad orage juice samples.

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BACKGROUND The aim of this work is the detection and quantification of bioaccumulated thiamethoxam (THM) in Zea mays at a silver electrode using square‐wave voltammetry. Thiamethoxam bioaccumulation and plant development were followed for 10 days from germination to seedling growth. Germination rate, accumulation rate, root length, and plant length were used as indicators. All experiments were carried out using several concentrations of THM (5.0 × 10−4, 1.0 × 10−3, 5.0 × 10−3, 3.4 × 10−2 and 5.0 × 10−2 mol L−1). RESULTS The results confirm that Zea mays was sensitive to this insecticide and that germination and growth inhibition were dose dependent. The efficiency and utility of the proposed method were discussed. The current intensity increases linearly with an increase in the THM bioaccumulated in Zea mays. After 10 days,the recovery results of the extraction of THM from zea Mayes samples spiked with different concentrations were encouraging. The detection and quantification limits were found to be 9.58 × 10−6 mol L−1 (3*SD/B) and 3.13 × 10−5 mol L−1 (10*SD/B). The precision was 2.67% for eight repetitions in a solution of 3.5 × 10−4 mol L−1 THM. Histological tests were also performed to confirm the effect of THM on the plant and showed that exposure to THM induced a net histological modification in the primary root tissue of Zea mays. CONCLUSION The use of THM can affect the quality of the plant crop yield, and its accumulation in edible plants could pose a potential risk for human and animal health if the insecticide intake were to exceed the recommended tolerable limits. © 2019 Society of Chemical Industry

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This work describes the catalytic property of silver nanoparticles decorated graphite electrode (Ag−CPE) for the thiamethoxam reduction. The prepared powders were characterized by X-ray diffraction (XRD), and the crystallite size of silver nanoparticles was calculated by the Scherrer equation. On the other hand, the electrochemical techniques were employed to study the nanoparticles size effect on the electrocatalytic reduction of thiamethoxam (TMX). The reduction current was proportional to thiamethoxam concentration in the range of 1.0 × 10 −4 to 1.0 × 10 −3 mol l −1 with a detection limit of 3.6 × 10 −5 mol l −1 . The modified electrode exhibited excellent reproducibility, accuracy and long-term stability of usage in water samples.