An Amperometric microsensor for the determination of H2S in aquatic environments

Abstract

A new amperometric microsensor for detection of dissolved H2S in aquatic 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 platinum guard electrode positioned in an outer glass casing (tip diameter 20-100 µm). Both working electrode and guard electrode were polarized 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 membrane and filled with a buffered electrolyte solution containing ferricyanide (K3[Fe(CN)6]) as redox mediator. Hydrogen sulfide penetrates the silicone membrane and is oxidized by K3[Fe(CN)6], resulting in the formation of elemental sulfur and ferrocyanide (K4[Fe(CN)6]). The latter is electrochemically reoxidized at the exposed end of the platinum working electrode, thereby creating a current that is directly proportional to the dissolved H2S concentration at the sensor tip. The sensor was characterized and calibrated in a flow-through cell combined with a coulometric sulfide generator. Difficult studies including the determination of H2S with high spatial and temporal resolution seem to be possible.