Simplified design of the coulometric sensor-actuator system by the application of a time-dependent actuator current

Acid or base concentrations can be determined by performing an acid-base titration with coulometrically generated OH¿ or H+ ions at a noble metal actuator electrode in close proximity to the pH-sensitive gate of an ISFET. It is shown, both theoretically and experimentally, that the relation between the acid or base concentration and the time needed to reach the equivalence point in the resulting titration curve is linear in the case where the current through the actuator electrode varies with the square root of time. In addition, this square root of time-dependent actuator current results in an increased acid-to-base (and vice versa) transition speed at the equivalence point when compared to a constant actuator current pulse, enabling the equivalence point to be detected more accurately and easily.