An Amperometric Microsensor for the Determination of H_2S in Aquatic Environments

摘要

A new amperometric micrdsensor for detection of dissolved H_2S 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 (K_3[Fe(CN)_6]) as redox mediator. Hydrogen sulfide penetrates 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 the platinum working electrode, thereby creating a current that is directly proportional to the dissolvedH_2S concentration at the sensor tip. The Sensor was characterized and calibrated in a flow-through cell combined with a cbulometric suffide generator. Difficult studies including the determination of H_2S with high spatial and temporal resolution seem to be possible.