Traceability of pH Measurements

The free acidity of an aqueous solution is usually expressed in terms of its pH, a measure of the hydrogen ions activity. Being the most often measured chemical parameter, pH values are meant to be used either in the assessment of other chemical species or in comparison exercises. The validity of conclusions requires that the values of pH measurements are linked through common references. Measurements are performed in pH meters submitted to prior calibration with reference pH buffers whose pH values have been established against conventionally assigned pH values of primary pH buffer standards. This chain of operations is supported on the quality associated with, namely, buffers, electrodes, procedures, calculations and model assumptions.

An overview will be given on recent fundamental and applied studies addressing these various issues, for the particular case of highly saline waters approaching the complex composition of seawater.