Electrochemical reduction of sulfite based on gold nanoparticles/silsesquioxane-modified electrode

This paper reports the synthesis and characterization of the water-soluble form of 3-n-propyl(4-methylpyridinium) silsesquioxane chloride (Si4Pic+Cl−), which showed potential for application as a stabilizing agent for gold nanoparticles (AuNP). Dispersed and stable suspensions of nanoparticles, with an average diameter of 45 nm, were obtained. Carbon paste electrodes modified with gold nanoparticles and Si4Pic+Cl− were constructed and applied in the detection and quantification of sulfite in acidic medium. Under these conditions, sulfur is in the electroactive form (sulfur dioxide) with a typical reduction peak at ca. −0.35 V (vs. SCE). Considering the voltammetric signal for sulfite, the electrode modified with AuNP (CPE/Au-Si4Pic+Cl−) showed an electrocatalytic effect of ca. −0.20 V compared to the bare electrode. In the square-wave voltammetry analysis, under optimized experimental conditions, the reduction peak increased with an increasing concentration of sulfite in the range of 2.54 to 48.6 mg L−1. The calculated LOD and LOQ values for sulfite were 0.88 and 2.68 mg L−1, respectively. The proposed method was successfully applied to white wine and coconut water samples, and no matrix effects were noted. Validation was performed through a comparison with results obtained by iodimetric titration. In recovery tests, the percentage recovery varied from 98 to 103% (n = 3).

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