D Cyclic Voltammetry

Excitation signals for potential scan voltammetries (a) linear sweep voltammetry (b-d) cyclic voltammetry (CV). 

Fig. 26a-d. Cyclic voltammetry of p-cresolmethylhydroxylase (PCMH) at a POE electrode in the presence of spermine as promoter. Electrolyte comprised 10 mM HEPES, 10 mM KCl (pH 7.4), scan rate 5 mVs (a) Spermine tetrachloride(10 mM) alone, (b) Response after addition of PCMH to 35 pM. (c) as for (b) but recorded at 0.1 current gain, (d) as for (c) but upon addition of the substrate p-cresol to 3 mM. Redrawn from Ref. 228, with kind permission... 

Figure 11.3 Typical features and behavior of traditional or new carbon pastes and the respective electrodes in current flow measurements, (a-d) Cyclic voltammetry of [Fe(CN)g]3/ - in 0.1 M KCI, c(Fe) = 5mM, lighter line, GCE (a,b) or GC-IL (c,d), hitherto unpublished records (e) Adsorptive stripping voltammetry of Ni" at the low parts per billion level in 0.1 M ammonia buffer containing 10 iM DMG (dimethyl glyoxime)H-Hg". Legend curve (1) blank, (2) c(Ni") = 5ppb, and (3) c(Ni") = 10 ppb. Note symbol Oj denotes the reductive response of oxygen...

Gosser, D. K., Jr., Cyclic Voltammetry Simulation and Analysis of Reaction Mechanisms, Wiley, Chichester, West Sussey, England, 1994. 

Centrifugal partition chromatography (CPC) has been used to characterize the partitioning behavior of hydrophilic molecules, where log D values as low as —3 can be obtained [371,377-379]. It is not as popular a method as it used to be, apparently due to instrumental challenges. Cyclic voltammetry (CV) has become the new method used to get access to very low log D values, with partition coefficients reported as low as —9.8 [261,269,362]. 

Fig. 5.18 Potentiostatic methods (A) single-pulse method, (B), (C) double-pulse methods (B for an electrocrystallization study and C for the study of products of electrolysis during the first pulse), (D) potential-sweep voltammetry, (E) triangular pulse voltammetry, (F) a series of pulses for electrode preparation, (G) cyclic voltammetry (the last pulse is recorded), (H) d.c. polarography (the electrode potential during the drop-time is considered constant this fact is expressed by the step function of time—actually the potential increases continuously), (I) a.c. polarography and (J) pulse polarography...

The electrochemical behavior of niclosamide was described on the basis of d.c. polarography, cyclic voltammetry, a.c. polarography, and differential pulse polar-ography, in the supported electrolytes of pH ranging from 2.0 to 12.0 [32], A tentative mechanism for the reduction of niclosamide is proposed that involves the transfer of 4 e . Parameters such as diffusion coefficients and heterogeneous forward rate constant values were evaluated. 

The variation of a with potential according to equation (13) may also be used to estimate the value of E°, from which the value of D may be inferred. This approach has been applied to organic peroxides,44 including endoperoxides of biological interest.37 Here again, convolution voltammetry proved to be more precise than plain cyclic voltammetry. 

The one-electron reduction potentials, (E°) for the phenoxyl-phenolate and phenoxyl-phenol couples in water (pH 2-13.5) have been measured by kinetic [pulse radiolysis (41)] and electrochemical methods (cyclic voltammetry). Table I summarizes some important results (41-50). The effect of substituents in the para position relative to the OH group has been studied in some detail. Methyl, methoxy, and hydroxy substituents decrease the redox potentials making the phe-noxyls more easily accessible while acetyls and carboxyls increase these values (42). Merenyi and co-workers (49) found a linear Hammett plot of log K = E°l0.059 versus Op values of substituents (the inductive Hammett parameter) in the 4 position, where E° in volts is the one-electron reduction potential of 4-substituted phenoxyls. They also reported the bond dissociation energies, D(O-H) (and electron affinities), of these phenols that span the range 75.5 kcal mol 1 for 4-amino-... 

Figure 11. Dependence of the perimeter P on the area A of the lakes on a logarithmic scale obtained at a height corresponding to 40% of the maximum height of the surfaces of (a) Pt/polished AL2O3, (b) Pt/etched Ni, and (c) Pt/unpolished AI2O3 electrodes. The slope S means (d log P / d log A). Reprinted from J. -Y. Go et al., A study on ionic diffusion towards self-affine fractal electrode by cyclic voltammetry and atomic force microscopy, J. Electroanal. Chem., 549 p. 49, Copyright 2003, with permission from Elsevier Science.

Parker, V. D. Precision in Linear Sweep and Cyclic Voltammetry, in Electronalytical Chemistry, Bard, A. J., Ed., Marcel Dekker New York, 1985, Vol. 14. 

The opposite situation (y/D/k -C <5), where the reaction layer is much thinner than the diffusion layer (as represented in the lower diagram of Figure 2.31) is more specific of electrochemistry, in the sense that the homogeneous follow-up reactions are more intimately connected with the electrode electron transfer step. The same pure kinetic conditions discussed earlier for cyclic voltammetry (Section 2.2.1) apply. In the case of a simple EC reaction scheme, as shown in the figure, the production of C in the bulk solution obeys exactly the same equations (2.32) to (2.34) as for B in the preceding case, as established in Section 6.2.8. 

Although separate determination of the kinetic and thermodynamic parameters of electron transfer to transient radicals is certainly important from a fundamental point of view, the cyclic voltammetric determination of the reduction potentials and dimerization parameters may be useful to devise preparative-scale strategies. In preparative-scale electrolysis (Section 2.3) these parameters are the same as in cyclic voltammetry after replacement in equations (2.39) and (2.40) of Fv/IZT by D/52. For example, a diffusion layer thickness S = 5 x 10-2 cm is equivalent to v = 0.01 V/s. The parameters thus adapted, with no necessity of separating the kinetic and thermodynamic parameters of electron transfer, may thus be used to defined optimized preparative-scale strategies according to the principles defined and illustrated in Section 2.4. 

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