In automation-enabled electrolyte analysis using ion-selective electrodes, what do the sensors measure, and which matrix effects can compromise results?

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Ion-selective electrodes measure the electrical potential at the sensor, which reflects the activity of the target ion in the solution rather than its raw concentration. The membrane potential that the electrode develops is tied to ion activity through the Nernst relationship, so the reading can be influenced by how ions interact with other species in the sample. In automated electrolyte analysis, matrix effects that can compromise results include proteins binding the target ion or altering the electrode surface, variations in ionic strength that change activity coefficients, and lipid components that foul the membrane or hinder ion access. These factors shift the effective ion activity seen by the electrode, causing drift or bias if not properly addressed. The other sensing approaches described in the choices rely on colorimetric changes, redox currents, or gravimetric mass, which are different measurement principles than ion-selective electrodes.