Ionenselektive

Ionenselektive is a term used to describe properties, materials, or devices that show a selective response to a specific ion in aqueous solution. In chemistry and analytical sensing, it is commonly associated with ion-selective electrodes and related membranes designed to target a single ion while suppressing interference from others. The concept underpins a range of sensors used for rapid, direct measurements of ionic species.

The core principle involves potentiometric sensing. An ion-selective electrode comprises a selective membrane separating a sample solution from an internal reference solution. The target ion interacts with the membrane (often via an ionophore or a charged additive), creating a potential difference at the interface. The measured potential follows a Nernstian response, typically about 59 mV per decade change in activity for monovalent ions at 25 °C. Selectivity against competing ions is quantified by selectivity coefficients, as described by the Nikolskii-Eisenman framework.

Materials and ionophores used in ionenselektive devices vary. Membranes are commonly polymeric, sometimes glassy or crystalline, and may incorporate ionophores such as valinomycin for potassium or crown ethers for sodium. These receptors confer high affinity for the target ion. Devices may be solid-state, coated-wire, or liquid-contact electrodes, and can be adapted for in situ or laboratory measurements.

Applications span clinical electrolyte analysis, environmental monitoring of water quality, soil and agricultural studies, and industrial process control. While ionenselektive sensors offer rapid, reagent-free measurements, they can be affected by interfering ions, ionic strength, temperature, and membrane aging, necessitating calibration and sometimes compensation for matrix effects.