Coulometry is an absolute method of ion generation. Provided that (1) the stoichiometry of the electrode reaction is known, (2) no side reactions occur, and (3) the current efficiency of the electrode reactions is close to 100%, the relation between the number of coulombs applied to the actuator and the amount of generated ions is fixed. Hence, the sensor signal can be adjusted to yield the read-out appropriate to the defined change in concentration by the generated ions. Note that this method of calibrating a pH sensor depends on the buffer capacity of the solution.