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

Abstract

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.