Traceability of pH Measurements

Abstract

The free acidity of an aqueous solution is expressed in terms of its pH, a measure of the hydrogen ions activity. Being the most often measured chemical parameter, pH is used in the assessment of other chemical species and in comparative exercises. The validity of conclusions requires that the values of pH measurements are traceable to common references and ultimately to the SI. Measurements are recommended 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 of low ionic strength, I≤ 0.1 mol kg-1. This chain of operations is supported on the quality associated with, namely, buffers, electrodes, procedures, calculations and model assumptions. An overview is given of recent fundamental and applied studies addressing these various issues, for the particular case of highly saline waters approaching the complex composition of seawater.