AN AMPEROMETRIC MICROSENSOR FOR THE DETERMINATION OF H2S IN AQUATIC ENVIRONMENTS

A new amperometric microsensor for detection of dissolved H2S in aquat ic environments was developed. The design of the microsensor is based on the same principle as the Clark-type oxygen microsensor. The sensor is equipped with a glass-coated platinum working electrode and a plat inum guard electrode positioned in an outer glass casing (tip diameter 20-100 mu m). Both working electrode and guard electrode were polariz ed at a fixed value in the range from +85 to +150 mV with respect to a counter electrode. The outer casing is sealed with a thin silicone me mbrane and filled with a buffered electrolyte solution containing ferr icyanide (K-3[Fe(CN)(6)]) as redox mediator. Hydrogen sulfide penetrat es the silicone membrane and is oxidized by K-3[Fe(CN)(6)], resulting in the formation of elemental sulfur and ferrocyanide (K-4-[Fe(CN)(6)] ). The latter is electrochemically reoxidized at the exposed end of th e platinum working electrode, thereby creating a current that is direc tly proportional to the dissolved H2S concentration at the sensor tip. The sensor was characterized and calibrated in a flow-through cell co mbined with a coulometric sulfide generator. Difficult studies includi ng the determination of H2S with high spatial and temporal resolution seem to be possible.