pH calibration of tetroxalate, tartrate and phthalate buffer solutions at above 100°C

Abstract

The pH_S of three standard buffer solutions has been measured using a hydrogen electrode against a silver–silver chloride electrode in a cell nominally without a liquid–liquid junction. The measurements have been carried out at 95–120°C in 0.05 mol kg^–1 potassium tetroxalate, 100–160°C in saturated (25°C) potassium hydrogen tartrate and 100–200°C in 0.05 mol kg^–1 potassium hydrogen phthalate solution. It has been shown that the method cannot be used to calibrate phosphate or borate buffers at >100°C because of excessive reduction of silver chloride by hydrogen, although such solutions remain useful buffers at elevated temperatures.