Potenciometrie

Potentiometry is a branch of electrochemistry that measures the electric potential of an electrochemical cell to determine the activity of ions in a solution, without drawing significant current. The measurement relies on a sensing electrode whose potential responds to the target ion and a reference electrode that provides a stable, known potential. The pair is connected to a high-impedance voltmeter to ensure that virtually no current flows.

The principle is based on the Nernst equation, which relates the measured potential to the activity (effective concentration) of the ion of interest and to temperature. Common sensing electrodes include glass electrodes for measuring hydrogen ion activity (pH) and ion-selective electrodes for specific ions such as Na+, K+, Ca2+, Cl−, and others. Because potentiometry measures potential rather than current, changes in the electrode potentials reflect changes in ion activity rather than instantaneous concentrations.

Techniques and applications include pH measurement, general ion-selective electrode measurements, and potentiometric titration. In potentiometric titration, the potential is recorded as a titrant is added, and the endpoint is inferred from a characteristic change in the potential. Potentiometry is widely used in environmental monitoring, clinical chemistry, food and beverage analysis, and industrial process control.

Calibration and limitations are important considerations. Readings depend on ion activity and require temperature control and calibration with standard solutions. Potential issues include junction potentials, electrode selectivity and interference from other ions, drift and fouling of the electrode, and the stability of the reference electrode. Despite these challenges, potentiometry remains a fundamental, widely used analytical technique.