STEPPED-POTENTIAL VOLTAMMETRIES AT STATIONARY ELECTRODES .2. NORMAL PULSE VOLTAMMETRY AND RELATED METHODS

Normal pulse voltammetry (NPV) and related methods at stationary elect rodes are reviewed. These methods involve the application to the same electrode of a sequence of potential steps occurring between a constan t potential and another which is gradually incremented. The voltammogr ams are obtained by taking the difference between the currents sampled near the end of two consecutive potentials steps. When the reaction r esulting from the return to the constant potential behaves reversibly, whatever the duration of the pulses, a depletion effect is not observ ed on the differential current. Therefore any value for the constant p otential can be chosen for a fast electrochemical system, whereas for a slow system this value must be sufficiently far from EO. For experim ental convenience and particularly to avoid the contamination on the e lectrode, the voltammograms must be obtained as quickly as possible us ing pulses of short and equal duration. Under these conditions, the di fferential current for a reversible system in NPV is 1.2 times the cor responding current at a renewable electrode. It seems that, for an irr eversible system, this factor is the same at any potential, as was fou nd by comparing irreversible waves for U(VI) in carbonate medium at a static and a renewable mercury drop electrode.