Electrooxidation of Sulfite Ions on a Composite Carbon-Containing Electrode Modified with Submicron Gold Particles

Abstract

Regularities of the electrooxidation of sulfite ions in an alkaline medium (рН ≥ 8; LiClO4, KNO3, Na2SO4, NaOH) on a composite carbon-containing electrode modified by submicron (300 nm or smaller) gold particles are studied using cyclic voltammetry. The electrocatalytic nature of the analytical signal is substantiated; a scheme of the oxidation process is proposed. A procedure for the preliminary electrochemical treatment of the modified electrode, ensuring an increase in the substrate oxidation current and consisting in the anodic polarization of the electrode in the potential range 0.9–1.4 V (Ag/AgCl reference electrode) in a supporting electrolyte is optimized. The essence of activation is an increase in the surface area of gold particles participating in the catalytic generation/reduction cycle of gold (hydr)oxides and providing an increase in the value of the analytical signal. The proposed approach ensures a significant increase of the sensitivity of the voltammetric method for determining sulfite ions. The concentration dependence of the analytical signal is linear in the concentration range of $${\text{SO}}_{3}^{{2 - }}$$ -ions 1 × 10–7–2 × 10–4 М (limit of detection 5.5 × 10–8 M). The results of the determination of sulfite ions in wines, beer, and juices indicate a higher accuracy of the voltammetric method compared to the standard iodometric procedure.