Conventional peak potential measurements

Using either X— Y or analog oscillographic recording, the location of the peak potentials during LSV or CV analysis cannot be determined much more precisely than 5 mV. Errors of such magnitude obviously can only be used for highly qualitative work and are totally unsuitable for electrode kinetic studies. 

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A study of the electrochemical oxidation and reduction of certain isoindoles (and isobenzofurans) has been made, using cyclic voltammetry. The reduction wave was found to be twice the height of the oxidation wave, and conventional polarography confirmed that reduction involved a two-electron transfer. Peak potential measurements and electrochemiluminescence intensities (see Section IV, E) are consistent vidth cation radicals as intermediates. The relatively long lifetime of these intermediates is attributed to steric shielding by the phenyl groups rather than electron delocalization (Table VIII). 

Fig. 7.52 Electrode reaction of azobenzene at HMDE. The dependence of the peak potential separation of conventional voltammograms (a) and potential-corrected voltammograms (b) on the amplitude, measured at different frequencies ...

Sometimes, and this is one of the disadvantages of conventional analysis of cyclic voltammograms, it is not possible to measure the baseline with sufficient precision in order to measure /p a. However, it is a good approximation to apply the following expression in terms of the peak current measured from the current axis (/p,a)o and the current at the inversion potential (/A)0 (see Fig. 9.2)... 

The manner in which kinetic data are treated in arriving at an electrode mechanism depends primarily upon whether the technique gives a direct measure of the response of the intermediate or an indirect measure, usually the effect of the chemical reaction on the electrode response of the substrate. In the former case, the conventional way of handling the data is to compare the experimental response with theoretical data in the form of a working curve and determine the mechanism from the best fit with theoretical data. The latter case usually involves the calculation of the electrode response to a particular mechanism and then comparing some measurable quantity, for example the sweep rate dependence of the peak potential, with the theoretical value. Which type of analysis is appropriate, direct or indirect, depends upon the... 

In conventional electrochemistry in solution, quantitation of analytes can be obtained by using several techniques. Thus, exhaustive electrolysis provides an absolute quantitation of an electroactive component in the sample. Voltammetric measurements (linear potential scan, cyclic, pulse, and square-wave techniques) can be used for determination of analytes in solution via calibration because peak currents (and peak areas) are usually proportional to the analyte concentration under fixed electrochemical conditions. 

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