Charging current polarographic wave

Clearly, the HMRDE curve gives a cleaner polarographic wave than does the RDE, the latter showing, in particular, a larger slope in the region of the limiting current, an effect directly connected to the double layer charging. 

Differential pulse voltammetry (DPV) is essentially an instrumental manipulation of chronoamperometry. It provides very high sensitivity because charging current is almost wholly eliminated. More important for CNS applications, it often helps to resolve oxidations which overlap in potential. The method combines linear potential sweep and square-wave techniques. The applied signal is shown in Fig. 16A and consists of short-duration square-wave pulses (<100 msec) with constant amplitude (typically 20 or 50 mV) and fixed repetition interval, superimposed on a slow linear potential scan. The Fapp waveform can be generated with a laboratory-built potentiostat, but most DPV work is done with a commercial pulse polarograph (see Appendix). The inset of Fig. 16A shows an enlargement of one pulse. The current is measured just before the pulse... 

The realization that current sampling on a step pulse can increase the detection sensitivity by increasing the faradaic/charging ratio is the basis for the development of various pulse voltammetric (or polarographic) techniques. Also, the pulses can be applied when it is necessary and can reduce the effect of diffusion on the analyte. Figure 18b. 11 shows the waveform and response for three commonly used pulse voltammetric techniques normal pulse voltammetry (NPY), differential pulse voltammetry (DPV), and square-wave voltammetry (SWV). 

A solvent, in addition to permitting the ionic charges to separate and the electrolyte solution to conduct an electrical current, also solvates the discrete ions, by ion-dipole or ion-induced dipole interactions and by more direct interactions, such as hydrogen bonding to anions or electron-pair donation to cations. Lewis acidity and basicity of the solvents affect the latter. The redox properties of the ions at an electrode depend on their being solvated, and the solvation effects electrode potentials or polarographic half-wave potentials. 

The voltammetric method, developed at ORNL for determination the [U(1V)]/[U(111)] ratio in the MSBR fuel salt [47], is based on measuring of the difference between the redox potential of the melt Feq and 1/2, the voltammetric equivalent of the standard redox potential of the U(1V)AJ(111) couple, at [U(IV)] S> [U(Ill)]. In conditions of linear voltammetry, at a stationary electrode and a reversible charge transfer of the melt-soluble oxidized and reduced forms of uranium, is approximately equal to the polarographic half-wave potential 1/2 and corresponds to the potential in the voltammogram, at which the current accounts for 85.2% of the peak current. The relationship between eq, 1/2 and [U(lV)]/[U(in)] ratio is given by the Nernst equation ... 

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