Abstract

Hydrogen ions are involved in a wide variety of chemical and biochemical reactions, the equilibria and kinetics of which are directly affected by the activity of these ions. This activity, expressed in terms of pH, is therefore of fundamental importance in many areas of science and technology; the determination of pH is one of the most widely performed analytical measurements, ranging in application from research and clinical laboratories to monitoring industrial processes.

Of the two methods for measuring pH, electrometric and chemical indicator (optical), the most common is based on the pH glass electrode used in combination with a reference electrode and pH meter. The indicator method, using pH-sensitive dyes, can be combined with optical readout devices, such as fiber optics and photometers, or simply by visual color comparison. The pH scale is defined by a series of reference buffer solutions which are used to calibrate the pH measurement system. Although pH measurements are among the most specific with respect to possible interferences, there are a number of potential sources of error that can affect the accuracy of the measurements. These errors, which include fouling of the electrodes, flow variations, suspended matter, temperature variation, and dehydration of the glass membrane in nonaqueous media, are discussed.