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

Normal pulse voltammetry (NPV) and related methods at stationary electrodes are reviewed. These methods involve the application to the same electrode of a sequence of potential steps occurring between a constant potential and another which is gradually incremented. The voltammograms are obtained by taking the difference between the currents sampled near the end of two consecutive potentials steps. When the reaction resulting from the return to the constant potential behaves reversibly, whatever the duration of the pulses, a depletion effect is not observed on the differential current. Therefore any value for the constant potential can be chosen for a fast electrochemical system, whereas for a slow system this value must be sufficiently far from EO. For experimental convenience and particularly to avoid the contamination on the electrode, the voltammograms must be obtained as quickly as possible using pulses of short and equal duration. Under these conditions, the differential current for a reversible system in NPV is 1.2 times the corresponding current at a renewable electrode. It seems that, for an irreversible system, this factor is the same at any potential, as was found by comparing irreversible waves for U(VI) in carbonate medium at a static and a renewable mercury drop electrode.