Acid or base concentrations can be determined by coulometric titration. A new all-iridium oxide sensor-actuator device is presented, of which the titrant is generated by a reversible redox reaction occurring in the electroactive iridium oxide actuator electrode, and the equivalence point in the titration curve is detected by the pH-sensitive iridium oxide sensor. The advantage with respect to the formerly used noble metal actuator electrode/ISFET sensor device is twofold: on the one hand, interference of Cl− ions, which oxidize at the noble metal actuator electrode during titration, is avoided and on the other hand, the preparation of the all-iridium oxide device is easier than of the ISFET-based devices. In addition to the conventional potential sweep method of oxide growth, a new current-pulse method is proposed, of which the parameters for optimal growth depend less on the pH of the solution.
Olthuis, W., van Kerkhof, J. C., van Kerkhof, J. C., Bergveld, P., Bos, M., & van der Linden, W. E. (1991). Preparation of iridium oxide and its application in sensor-actuator systems. Sensors and actuators. B: Chemical, 0(4), 151-156. https://doi.org/10.1016/0925-4005(91)80191-L