Construção de Eletrodos de Pasta de Carbono Modificados com Silsesquioxano e AuNPs Aplicados na Determinação de Sulfito

Silsesquioxane materials have been applied in several fieldsof Chemistry, with strong emphasis in Analytical Chemistry, as modified electrodes have been commonly developed[1-3]. Thus, we prepared gold nanoparticles stabilized with silsesquioxane polymer to modify carbon paste electrodes. The application of this new sensor(CPE/Au-Si4Pic+Cl-)is focused in the electroreduction of sulfite in acid media. According to the equilibria distribution of sulfur containing species, in very low pH the electroactive specie present in aqueous solution is dissolved SO2[4]. It was observed an electrochemically and chemically reversible redox couple with Erpat -0.35 V vs.SCE and a peak-to-peak separation close to 60 mVwhen CPE/Au-Si4Pic+Cl-is employed. Compared to bare CPE and the silsesquioxane (CPE/Si4Pic+Cl-) modified electrode there is a displacement of 20 mV(-0.55 V)for the reduction process, denotingthat AuNPs may electrocatalyze the reaction.Electrochemical Impedance Spectroscopy (EIS) measurements show thatRctofCPE/Au-Si4Pic+Cl-is lower when compared to others two electrodes, facilitating the electron transfer by a diffusional process. Thereduction peak was investigated by square wave voltammetry (SWV) and under optimized conditions; the calibration curve showed a linear range from 2.54 to 48.6 mg L-1of dissolved SO2 with a limit of detection of 0.88 mg L-1.The sensor demonstrated selectivityand stability, fairlyintra-day and inter-day repeatability and electrode-to-electrode repeatability, with relative standard deviations of 3.56 %, 4.23 % and 3.98 %, respectively. The proposed modified sensor was successfully applied to the determination of SO2 and sulfite in real samples as white wine and coconut water and the results were in agreement with those obtained using the iodimetric titration method. Recoveries of 98.1 to 103.5% were obtained, demonstrating the suitability of the proposed method to real sample analysis.