Assessment of glass electrodes for determining pH in boiler feed water

Six types of commercial glass electrodes have been tested in the laboratory for their suitability for measuring pH in ammonia-dosed boiler feedwater of moderately low specific conductivity (about 5 µS cm–1). The electrodes were chosen to represent the range of pH-sensitive glasses available. All of the electrodes showed a near-theoretical sensitivity, had stable standard potentials and responded sufficiently quickly. In the dilute ammonia solutions, however, the electrodes indicated pH values that could differ by as much as 0.3 pH unit when the solution was flowing slowly through the measuring cell. When the solution was stirred the maximum bias was 0.05 pH unit. For most industrial purposes, the differences in performance between the various types of electrode are unimportant and glass electrodes are less of a problem than reference electrodes for pH measurements in this type of water.