Multilayer potassium sensor based on solid-state coextraction

A highly selective solid state multilayer sensor is presented which enables fluorescence optical determination of potassium ions. It is based on co-extraction using valinomycin along with a fluorescent anion, both contained in different layers. The sensor membrane is composed of two layers of highly different lipophilicity. The lipophilic phase contains the carrier valinomycin whilst the hydrophilic phase contains the anionic fluorophore sulforhodamin B. On exposure to potassium ions, the lipophilic phase becomes fluorescent after coextraction of both potassium ions and the anionic fluorophore. To prevent leaching of th-dye, an additional blocking layer (nafion) was spread on the sensor. The dynamic range is from 0.1 to 50 mmol/l K+ with very low cross-sensitivity to pH and ionic strength. The response times vary from 1 to 2 h.