Glass electrode half-cells for measuring unified pH in ethanol–water mixtures

Abstract. The acidities of any given solvent or mixtures thereof can be compared by pH measurements on a unified scale, so-called pH abs H 2 O measurements. The method is quite new and has not been characterized with respect to metrological criteria to date. Metal solid-contact glass electrode half-cells, three commercial, conventional glass electrode half-cells with inner liquid filling and one pair of combined electrodes were used to investigate the stability of the measurement and the reproducibility of pH abs H 2 O results of ethanol mixtures with water. All electrodes are suitable for unified acidity measurements in standard aqueous buffers. In ethanol mixtures, the combined electrodes were found to be unsuitable. The half-cell electrodes can be reasonably used only in buffered solutions.