Technical Note: Measurement of pH in Concentrated Brines

To resolve reported discrepancies between pH values of concentrated brines measured in the laboratory and those predicted by thermodynamic models, extensive measurements have been carried out to compare the performance of several different types of a glass pH electrode against a standard hydrogen electrode (SHE). The results demonstrate that the use of glass electrodes to measure pH in concentrated sodium chloride solutions gives a misleadingly low indication of pH, and may introduce errors of up to 0.2 pH units. This small difference is usually not significant but if the target pH is near a step-change in corrosion behavior then consideration should be given to adopting the SHE as back-up.