PH determination on a carbonate buffer by Harned cells of different designs

Abstract

The carbonate solution is one of seven primary standard buffers set recently by the International Union of Pure and Applied Chemistry (IUPAC) recommendations (Buck et al., Pure Appl Chem 74:2169–2200, 2002). The peculiarity of the pH measurement of this buffer in a traditional Harned cell (classic cell) is due to the loss of carbon dioxide with hydrogen flow and the ensuing change of its chemical composition. This results in a continuous increase of the recorded electromotive force (E) of the cell. Therefore, almost all National Metrology Institutes (NMIs) are now using the extrapolation of measured E data to zero time point in order to find the initial pH. The National Metrology Institute of Japan (NMIJ) has developed a different design of Harned cell (NMIJ cell) with compensation of the lost carbon dioxide from the intermediary saturation vessel. The results of the study of the NMIJ cell are presented, together with those of the trilateral NMIJ–PTB–ZMK (NMI of Japan with the NMI of Germany [Physikalisch-Technische Bundesanstalt, PTB] and the German Centre for Measurements and Calibrations [Zentrum fur Messen und Kalibrieren GmbH, ZMK]) comparison of pH values for the carbonate solution in different designs of Harned cell.