A metal-catex composite electrode for determination of paraquat in various samples by Ad-differential pulse cathodic...

In this work, a novel kind of metal-catex composite electrode for determination of paraquat (PQ) by adsorptive differential pulse voltammetry is introduced. The metal-catex composite electrode was fabricated by cathodic electropolymerization of p-nitrophenol and p-nitrobenzoic acid in the presence of tin (II) chloride as a scaffold for composite structure on prepared glassy carbon electrode. Electropolymerization was carried out in sodium acetate medium. The surface of the fabricated electrode was characterized with field emission scanning electron microscope and energy-dispersive X-ray spectrometry. The obtained results show that there are Sn nanoparticles in the structure of the catex-composite. Chemical structure of metal-catex composite electrode was investigated using FTIR (ATR), ¹³C NMR, H NMR and a suitable mechanism for electropolymerization has been proposed. This metal-catex composite electrode was applied for determinations of PQ using sodium acetate buffer solutions at pH = 6.5 as an electrolyte solution. All parameters influencing the performance of the fabricated electrode were studied and optimized. The proposed electrode exhibits good linearity versus PQ concentration in the range of 3.8 × 10^-8 to 7.7 × 10^-7 mol L^-1 and shows a manifold increase in sensitivity (more than 30 times) as compared to the glassy carbon electrode. The LOQ of this electrode was 7.78 × 10^-9 mol L^-1, which is comparable with that of other electrochemical methods. The mean, standard deviation and relative standard deviation for seven repetitive determinations of paraquat (7.78 × 10^-8 mol L^-1) were measured to be 7.75 × 10^-8 mol L^-1, ±0.29 × 10^-8 mol L^-1, and 3.75% respectively. This electrode was applied for the determination of paraquat in natural water, natural juice, potatoes and onions. The introduced electrode shows good stability with repeated use and over long periods (about 20 days). There is a good agreement between the results for water analysis by this method and the standard method.