pH Analyzers

The concentration of hydrogen ion in aqueous solutions, or pH, is measured using pH analyzers (pH meters) in conjunction with electrochemical cells. This chapter provides an introduction to pH theory of aqueous electrolytes as it relates to the operational function of the pH electrode. The pH meter equation is introduced, and operational parameters that need to be controlled for accurate pH measurement are discussed in detail. Reference electrodes at either side of the pH membrane provide the electrolytic contacts necessary to allow measurement of the potential gradient across the membrane. A schematic diagram of a typical pH measuring cell is shown. Temperature affects electrometric pH measurement in two ways — through its effect on the electrodes and on the solutions. In clean solutions of nonaggressive chemicals at moderate temperature and pressure, pH probe reliability is measured in months. Finally, instrumental aspects of measurement amplifiers and intelligent pH analyzers are presented.