potentiometrically

Potentiometrically is an adverb used to describe measurements or analyses conducted by potentiometry, the electrochemical method that determines the electric potential difference between a working electrode and a reference electrode under negligible current. In potentiometric measurements, the measured potential is related to the activity of a specific ion or redox couple in the solution, rather than to the rate of electron transfer.

Principle: Potentiometry relies on the Nernst equation, which links electrode potential to the activity (effective concentration) of the ion of interest. With a suitable ion-selective or reference electrode, the resulting potential changes in a predictable way as ion activity changes. The measurement is typically conducted with high input impedance to minimize current flow, ensuring near-equilibrium conditions.

Instrumentation and methods: Common setups include a reference electrode (such as Ag/AgCl or saturated calomel) and a selective working electrode or glass pH electrode. A high-impedance voltmeter records the potential; temperature control and proper calibration with standards are important for quantitative work. Potentiometric titration uses a similar arrangement with a titrant added and the endpoint determined from a characteristic potential change.

Applications and limitations: Potentiometric methods underpin pH measurement, ion-selective electrode analysis for ions such as K+, Na+, Ca2+, and redox potential measurements. Advantages include simplicity, speed, and little sample consumption. Limitations involve electrode selectivity, junction potentials, temperature sensitivity, and the need for stable reference electrode conditions. Interfering species and activity coefficients can affect accuracy.