Amperometric sulfur dioxide gas sensor with dimethyl sulfoxide as solvent for internal electrolyte solution

An amperometric sensor for atmospheric sulfur dioxide based on a classical three-electrode cell configuration equipped with a microporous Teflon membrane is presented. The measured current, directly associated with oxidation of SO2 on a gold electrode, is related to the SO2 level. Various electrolyte solutions, including aqueous H2SO4, HClO4, HClO4–H2SO4 mixtures and Li2SO4 and also solutions of H2SO4 and HClO4 in dimethyl sulfoxide (DMSO)–water solvent mixture, were tested. The high sensitivity, up to 45 nA ppm–1 (0.9 µA cm–2 ppm–1) SO2, was achieved when the sensor was filled with 5 M H2SO4 in DMSO–H2O with an H2O:DMSO mole ratio of 2. The respective value for standard 5 M H2SO4 electrolyte solution was only 0.5 nA ppm–1 SO2. The high sensitivity and advantages resulting from the use of an organic solvent (DMSO) are discussed.