Which of the following measurements is performed using potentiometry?

Potentiometry is a technique that measures the voltage of a solution to determine the concentration of ions in that solution. It is particularly well-suited for pH measurement, which reflects the hydrogen ion concentration. The pH meter operates using a glass electrode that responds to hydrogen ions, providing a voltage output that correlates to the pH level. This direct relationship enables accurate and quick pH determinations, which are crucial in various clinical and environmental samples.

In contrast, enzyme activity is typically measured through kinetic assays that assess the rate of product formation or substrate consumption, which does not involve potentiometric principles. Specific gravity is determined by comparing the density of a substance to that of water, often using hydrometers or densitometers rather than electrical measurements. Thermal analysis involves measurements of physical or chemical changes as a function of temperature and does not relate to voltage or ion concentration.

Thus, the choice pertaining to pH measurement is the clear example of potentiometry in action, highlighting its applicability in clinical chemistry.