Tetrachloro-ortho-Benzoquinone as Catalyst for Electrocatalytic Oxidation of Sulfite in Acidic Media and its Analytical Application

A chemically modified carbon paste electrode (MCPE) with tetrachloro-orthobenzoquinone (TOB) was employed to study the electrocatalytic oxidation of sulfite in aqueous solution using cyclic voltammetry (CV) and double-potential step chronoamperometry. It has been found that under an optimum condition (pH 2.0), the oxidation of sulfite at the surface of MCPE occurs at a potential of about 700 mV less positive than that of an unmodified CPE. The diffusion coefficient (D) for sulfite was found as 8.2×10-6 cm2 s-1 by chronoamperometry. The electron transfer coefficient, a, was estimated to be 0.4 and 0.24 for the oxidation of sulfite at the surface of MCPE and unmodified CPE, respectively. The electrocatalytic oxidation peak currents showed a linear dependence on the sulfite concentration in the range of 1×10-4 M -4.2×10-3 M with detection limit (3s) 5.7×10-5 M by CV. This method was also used for selective determination of sulfite in weak liquor