Determination of Sulfur Dioxide by Reaction with Electrogenerated Bromine in a Thin-Layer Cell Having a Gas-Porous Wall

An electrochemical sensor is described for the determination of ambient sulfur dioxide by reaction with electrochemically generated bromine in a thin-layer cell. Sulfur dioxide in the gas phase diffuses through a porous, hydrophobic membrane into a thin layer of solution in which bromine is generated electrochemically. The quantity of bromine at the gas-solution interface is determined by reduction at a gold cathode situated on the solution side of the porous wall separating the gas phase from the solution phase. The diffusion of sulfur dioxide through the porous membrane into the thin-layer cell decreases the amount of bromine reaching the gold cathode. This decrease produces a change in current that Is proportional to the concentration of sulfur dioxide in the gas phase. The device was evaluated for sensitivity and stability for the determination of parts-per-million levels of sulfur dioxide.