Electrochemistry of sulfur dioxide, polyphenols and ascorbic acid at poly(3,4-ethylenedioxythiophene) modified electrodes

Cyclic voltammetry was used to investigate the electrochemistry of sulfur dioxide, polyphenols and ascorbic acid in a pH 3.3 model wine solution (0.033 M tartaric acid and 12 vol% ethanol) at conducting polymer electrodes. The oxidation of sulfur dioxide, an important wine preservative, was successfully achieved using poly(3,4-ethylenedioxythiophene) (PEDOT) as a redox mediator grown electrochemically on a gold electrode. The deposition conditions and the film thickness were investigated for their effects on the oxidation current due to free sulfur dioxide.The simultaneous detection of sulfur dioxide and wine polyphenols using voltammetry is challenging, as the oxidation potentials lie close to each other. Four representative white wine polyphenols were investigated in combination with sulfur dioxide. It was found that the oxidation current at a PEDOT covered gold electrode increased linearly at 760 mV (Ag/AgCl) with increasing sulfur dioxide concentrations, and largely independent of the earlier polyphenol oxidation peak at around 400 mV. Through the addition of acetaldehyde, a subtractive measure of free sulfur dioxide concentration was obtained. At the PEDOT electrodes, ascorbic acid oxidation with a 240 mV peak was well separated from the main polyphenol oxidation peak, and unlike the merging of peaks seen at glassy carbon electrodes.