Voltammetry peak height

Randles-Sev ik plot A graph derived from the Randles-Sev5ik equation, showing a plot of the cyclic voltammetry peak height Ip, (as y ) as a function of (as x ), where v is the scan rate. 

Fig. 4.7. The voltammetry peak height, Jp, as it varies with scan rate, cr, for planar, cylindrical and spherical electrodes for = 10 .

A quick and non-destructive method for measuring relative reactivities of two nucleophiles towards the same aryl radical derives from repetitive cyclic voltammetry of a solution containing the substrate and the two nucleophiles (Amatore et ai, 1985b). The ratio of the peak heights corresponding to the two substitution products provides straightforwardly the ratio of the two rate constants. 

The voltammogram for jamesonite is given in Fig. 2.21. It can be seen that there are four obvious anodic peaks at the first cycle voltammetry. The peak current of api, aps and cp2 constantly increase with the number of cycle adding, but the peak height of ap2 and ap4 decreases at the second cycle and then keeps constant even by multi-cycle according to the experimental appearances. It was... 

Differential pulse voltammetry is particularly susceptible to adsorption of species on the electrode, which can have drastic implications for peak shape. If adsorption is suspected, then peak area should be used rather than peak height... 

In the case of dissociative electron transfer to aromatic compounds, electron transfer is not necessarily concerted with bond dissociation. The substrate 7t-radical-anion may be an intermediate whose existence can be demonstrated by fast scan cyclic voltammetry in aptotic solvents. At fast scan rates, reversible electron transfer occurs. At slower scan rates, die anodic peak height falls and a second reversible electron transfer step appears due to formation of the radical-anion of the compound formed by replacement of the substituent by hydrogen. Cleavage of the... 

In linear sweep voltammetry, the potential is varied linearly versus time, and current peaks are registered in correspondence to oxidation or reduction (depending on the potential variation verse) of the analytes. The potential value associated to a peak is characteristic of the specie being oxidizing or reducing, while the peak height can be employed for quantitative purposes. 

In the case of Cyclic Square Wave Voltammetry (CSWV), the SWV curve obtained in the second scan is a mirror image to that of the first scan whatever the electrode geometry if the diffusion coefficients of species O and R are assumed as equal. In the contrary case, although the peak potentials of both scans are coincident, differences in the peak heights are observed for nonplanar electrodes. 

As in the case of differential double potential pulse techniques like DDPV, slow electrochemical reactions lead to a decrease in the peak height and a broadening of the response of differential multipulse and square wave voltammetries as compared with the response obtained for a Nemstian process. Moreover, the peak potential depends on the rate constant and is typically shifted toward more negative potentials (when a reduction is considered) as the rate constant or the pulse length decreases. SWV is the most interesting technique for the analysis of non-reversible electrochemical reactions since it presents unique features which allow us to characterize the process (see below). Hereinafter, unless expressly stated, a Butler-Volmer potential dependence is assumed for the rate constants (see Sect. 1.7.1). 

Both single-sweep and cyclic voltammetry can provide information about the approximate number of electrons transferred in each wave or peak. This is done by comparing the plateau or peak height with that of a known one- or two-electron transfer process under identical conditions (as an example, the oxidation of 9,10-diphenylanthracene to the cation radical is a commonly used reference reaction). 

Applications of pulse techniques in electrochemistry have been predominantly in the area of analysis, relying on the linear dependence of peak height on potential, although recently their use in mechanistic studies, particularly square-wave voltammetry, has begun to be exploited. The reason for their use in analysis is intimately linked with the low detection limits that are attainable, particularly in combination with pre-concentration techniques, as will be seen in Chapter 14. Finally, since nowadays the pulse sequences are generally controlled and responses analysed using microprocessors, the development of new waveforms for particular situations is now a much easier task than it was even a decade ago. 

Peak height (in -> voltammetry) — It is the maximum current in - linear scan voltammetry, -> cyclic voltammetry, - staircase voltammetry, - differential staircase voltammetry, -> alternating current polarography... 

El 12 for the waves was taken at 85 % of the peak height observed in cyclic voltammetry, at scan rates up to 45 V s " (Refs 73-75). Potentials in Ref. 79 were measured by second harmonic AC polarography. 

Neeb, R. Kiehnast, I.Z. Effect of salts on the anodic peak height in inverse voltammetry. Anal. Chem. 1967,241, 142-155. 

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