Electrochemistry Theory And Practice

An electrochemical cell for pH measurement always consists of an indicating electrode whose potential is directly proportional to pH, a reference electrode whose potential is independent of pH, and the aqueous sample to be measured. If all three parts are in contact with each other, a potential can be measured between the indicating electrode and the reference electrode, which depends on the pH of the sample and its temperature.

Because of the complexity of a pH measurement, the combination of indicating and reference electrode must be calibrated in advance, to compensate for slight changes over time. See chapter “calibration”.