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Platinum Metals Rev., 1991, 35, (3), 137

Iridium Oxide Device for Coulombic Titrations


When determining the acidity or basicity of a solution by coulombic titrations, an actuator electrode is positioned close to the pH sensitive gate of an ion sensitive field effect transistor. The ISFET acts as the indicator electrode to establish the equivalence point in the titration. However, in this system, the operating potentials of the actuator electrode are such mat any other redox couple in the solution, or any chloride ions present, will interfere.

Now, however, an all iridium oxide sensor-actuator system has been proposed by researchers at the University of Twente, The Netherlands, and tested for such titrations (W. Olthuis, J. C. Van Kerkhof, P. Bergveld, M. Bos and W. E. Van Der Linden, Sens. Actuators B, 1991, 4, (1&2), 151–156). Since the reversible redox reaction at an iridium oxide electrode functions at a favourable potential, it is suitable for use as the actuator electrode, with a pH sensitive iridium oxide sensor determining the equivalence point. Such a system eliminates interference from any chloride ions present. The preparation of this system is reported to be easier than the preparation of conventional ISFET-based devices.

The authors go on to describe a new current-pulse method of producing iridium oxide where the growth parameters are independent of the pH of the growth solution.