pHmeters

A pH meter is a scientific instrument used to measure the acidity or basicity of a solution by determining its pH, a logarithmic measure of hydrogen ion activity. Modern pH meters consist of a pH-sensitive electrode, usually a glass combination electrode, connected to a high-impedance electronic meter, and often a reference electrode. The glass electrode develops a potential proportional to the hydrogen ion concentration, which is measured against the reference electrode; the instrument converts this potential into a pH value, typically with automatic temperature compensation.

Types and configurations include benchtop meters that offer high accuracy and stability, handheld meters for field use, and combination electrodes that integrate sensing and reference in a single probe. Specialized microelectrodes are used for small samples or viscous media.

Calibration and measurement involve using standard buffer solutions to set reference points, commonly pH 4, 7, and 10. Calibration can be two-point or three-point, and temperature compensation improves accuracy since readings depend on temperature. The electrode requires proper maintenance, including storage in suitable storage solutions when not in use and periodic recalibration.

Applications span chemistry, biology, medicine, food and beverage, environmental monitoring, agriculture, and education. Maintenance and performance depend on regular cleaning, proper storage, and timely replacement of worn electrodes. Typical commercial meters offer ±0.01–0.1 pH unit accuracy, influenced by probe quality and calibration conditions.

Standard methods and guidelines, such as ISO 10523, describe proper procedures for pH measurement with glass electrodes. Limitations include interference from colored or highly buffered solutions, high ionic strength, air bubbles, and electrode aging.