Absolute salinity determination by oscillation-type densimetry and refractometry

The determination of salinity values from SI traceable densimetry and refractometry measurement results enable SI traceability of the former. In this work, a short study of the metrological compatibility of salinity determinations via these two methods for sodium chloride in ultrapure water solutions and two different standard seawaters (OSIL and ERM) solutions, in the [35.0; 215.0] g kg−1 interval, is presented. It evidenced the metrological compatibility of the salinity determinations in the referred interval. The largest salinity values enabled to test the matrix effect upon the determinations and concluded the preferable use of densimetry technique, when occurring

Symmetric Potentiometric Cells for the Measurement of Unified pH Values

A unified pH scale of absolute values (pHabs scale) enables the comparison of acidities in different solvents. To date, very few different experimental setups have been used for the measurement of values on this scale. The article describes the design and performance of the different symmetric cells used for unified pH measurement by several institutions. Well-established and reliable standard aqueous buffer solutions are the first step of method validation necessary to achieve a robust metrological level for more complex media. The pH of aqueous standard buffers was measured by differential potentiometry, where the potential between two glass electrodes is measured directly. All the tested electrochemical cells prove to be suitable for unified pH measurements. This validation highlights that the method is, to a large extent, independent of the used equipment, including the cell geometry. The inherent symmetry of the cell design helps to reduce the experimental workload and improve the accuracy of obtained results