Nonclassical Potentiometric Indicator Electrodes with Dual Sensitivity

Classically all titrations are divided into four groups: acid-base, redox, precipitation and complexometric. Correspondingly, four kinds of potentiometric indicator electrodes can be distinguished: pH, redox, anionic and cationic. By deliberate exploitation of the mixed conductivity of conducting polymers, a new class of indicator electrodes has been designed. With these electrodes, unique potentiometric titrations can be performed with titration jumps that originate from a change in redox potential and a change in ion activity and monitored by the same indicator electrode in the course of titration. The mechanism of the indicator electrode with dual sensitivity is discussed, the theoretical implications of the application of such electrodes in stepwise titrations are outlined, and model experimental titrations, including an unusual redox-precipitation titration, are presented.