Coulometric micro-titrator with a ruthenium dioxide pH-electrode

A coulometric diffusional titrator with a ruthenium dioxide pH-sensing electrode for the end-point detection in acid-base titrations is presented. The device was prepared by galvanic deposition of noble metals onto electrodes etched on a copper clad printed circuit board. Five electrodes were employed: three gold electrodes (two actuator and one counter) for the coulometric production of the titrating protons or hydroxide ions, and a RuO2-electrode and Ag/AgCl pseudo-reference electrode pair for the end-point detection. The RuO2-electrode for pH-measurements showed a linear response to the variation of the pH-value in the range from 2 to 12 pH-units and was useable for a period of 3 months. The device was found to yield linear relationships between the analyte concentration and the equivalence time for concentration ranges of acetic acid and ammonia between about 0.1 and 100 mM. (C) 2000 Elsevier Science B.V. All rights reserved.