Half peak width

Table 2.1 Square-wave voltammetry of fast and reversible electrode reaction (1.1). The dimensionless net peak current, the ratio of peak currents of the forward and backward components, the peak potentials of the components and the half-peak width as functions of SW amplitude ...

Fig. 2.2 The dependence of the dimensionless net peak current (i) and the ratio of the dimensionless net peak current and the half-peak width (2) on the product of number of electrons and the square-wave amplitude...

The half-peak width, AEp/2, of the quasireversible reaction increases with decreasing If, but Aiip/2 of totally irreversible reactions is independent of if. 

Although it is difficult to generalize the dependence of the peak potential on e, in general, for an oxidative electrode mechanism, the position of the peak shifts to positive potentials by increasing the rate of the preceding chemical reaction. At the same time, the half-peak width is largely insensitive to the chemical reaction. If log( ) < -2, Ap vs. log(e) is a linear function with a slope of about 30 mV. 

Berberine is an alkaloid undergoing an irreversible four-electron and three-proton reduction to the electrochemically inactive compound canadine, which is also adsorbed on the mercury electrode surface. As predicted by the theory, the net peak current of berberine is a linear function of the frequency, whereas the peak current shifts linearly with log(/) with a slope of -45 mV. Based on the theoretically predicted value for the half-peak width, AE p/2 = (63.5 0.5) / c mV, the catho-... 

The transfer of anions (CIO4, NO3, SCN , Br , and Cl ) and cations ((CH3)4N+, (C4H9)4N+, Na+, and K+) has been studied according to mechanism (4.12) and (4.13), respectively. In all cases, the voltammetric curves were particularly well developed, with a virtnally constant peak potential and half-peak width, indicating no effect of uncompensated resistance. In all experiments, the transferring ion was... 

Screen-printed carbon electrodes were also evaluated in the Topas microchip for separation and detection of pAP and AsA. The theoretical plate number (AO, half-peak width (wy2), peak current and resolution are also shown in Table 34.2. Peak current at SPEs was higher than those obtained with gold and platinum wires. 

A gold film was also evaluated using pAP as analyte model. The theoretical plate number (AO was 5990 m-1 with a half-peak width (wy2) of 4.1s for pAP. Peak current at gold-film electrode was lower than at SPEs but higher than at gold and platinum wire. 

Injection voltage is varied between +500 and + 2000 V and maintained for 5, 10, and 20 s. Separation is carried out by applying a voltage of +2000 V using a detection potential of +0.7 V and 50 mM Tris-based buffer pH 9.0. Choose optimal injection time/voltage taking into account of peak current (7P) and half-peak width (1U1/2). 

Optimal detection potential, separation voltage, and injection time/ voltage are used to determine parameters such as electroosmotic velocity (ueo = Leff/tm) and mobility (/[Pg.1282]

The response curve, a voltammogram, for a reversible one-electron reduction is shown in Fig. 6.9 its characteristic feature is the presence of two peaks. The position, the height and the broadness of each peak are given by the peak potentials, ped and °x, the peak currents, ixed and i°x, and the half-peak widths, E d - and °x - E°x2, where ed and °x2 are the values of the potential at i = i 1 and i = /°x, respectively. The presence of peaks in the voltammogram is understood by inspection of the concentration profiles shown in Fig. 6.10. In comparison with CA experiments discussed above, it is seen that the gradient during the early part of the CV experiment is not very steep, which is because [O]x=0 in the... 

In all the cases shown in Fig. 4.25, the peak potential corresponds to the formal potential of the charge transfer process, Ec peak = Et°, with this behavior being characteristic of the catalytic mechanism and of reversible charge transfer processes (reversible E mechanism see Eq. (4.85)). The half-peak width (W /2) is independent of the electrode geometry and size and the catalytic rate constants and is given by... 

Fig. 6.26 Peak parameters of the CV curves (peak potentials (a) peak heights (b) half-peak widths (c)) calculated by generating voltammograms from Eqs. (6.160) and (6.166) for different values of the dimensionless rate constant Q. The values of a appear on the curves. Letters a and c in figure c correspond to anodic and cathodic curves, respectively...

The evolution of the peak parameters of the (i/r y — ) response with AEC° (peak potentials (a), peak heights (b), and half-peak width (c)) for a two-electron transfer can be seen in Fig. 6.29. In Fig. 6.29a, the peak potentials refer to the average... 

Figure 6.29c shows that the half-peak width, WV2, changes in the extreme negative and positive values of AE between 90 mV (E c ) and 45 mV (Ei e-) for an EE process, but a sharp jump in the half-peak width, WV2, is observed at AEf + —135 mV, which corresponds to a y/ — E curve with two peaks, whose central trough is situated just at the half-peak height. As in the case of the peak current, a theoretical expression has been reported for the half-peak width when only one peak appears [66, 67] ... 

Fig. 7.8 Variation of the half-peak width (Wi/2, Eq. (7.32)) of the SWV curve with the square wave amplitude ( sw) for the four geometries considered discs, spheres, cylinders, and bands. A s = 5mV. T= 298.15 K...

Concerning the peak potential shown in Fig. 7.16b, for slow charge transfers, its value moves away from the formal potential E (which coincides with the peak potential for fast charge transfers) toward negative values, and the shift is more pronounced the smaller a. The half-peak width of the SWV net current increases as the charge transfer evolves from fast to slow (see Fig. 7.16c) becoming independent of Kplane for values of the rate constant below 0.01 and a > 0.3. In the case of a reduction process, some anomalies in the general trend are observed for low values of a (see below). 

As in the case of a reversible one-electron electrochemical reaction, the halfpeak width of the SWV does not depend on the electrode geometry. For a two-electron electrochemical reaction, Wy2 is only a function of the difference between formal potentials AE f and of the square wave amplitude sw. The evolution of the half-peak width Wy2 with AEcspherical electrodes has been plotted in Fig. 7.32. These curves give a very general criterion for the characterization of the EE process through Wy2. 

The half-peak width takes a constant value when two separate peaks are obtained, which corresponds to the width of mono-electronic transfers W j2 ( sw > 0) 90mV. For AEc — 142.4mV, two unresolved peaks or a... 

Both peaks in the curve obtained at Esw = 10 mV have a half-peak width of Wi/2 = 90 mV, whereas for higher values of sw the peaks become wider and less defined, reaching the value W1/2 = 2 sw for each of the peaks at curves corresponding to Esw = 100 and 200 mV. These peaks are already clearly transformed into two plateaus for Esw = 200 mV, which merge into a whole plateau for Esw A /2 (see curve with Esw = 250mV in Fig. 7.33a) with height 7EE,sphe,plateaU(- sw = 250my) = 27 1 pA. 

Concerning the half-peak width (W1/2), as can be deduced from Fig. 7.36, its value is independent of the electrode radius and the catalytic rate constants. The dependence ofWul on the square wave amplitude is identical to that obtained for a simple charge transfer given by Eq. (7.32) (see also Fig. 7.8), i.e., it increases with Sw from W1/2 = 90mV for Esw < lOmV to Wy2 = 2 Sw for sw > lOOmV. 

The peak potential is generally shifted toward more negative values as /sw increases for a given value of the equilibrium constant Kcq, and more noticeably the smaller the Keq value. The half-peak width is slightly affected by the kinetics parameter of the chemical reaction. 

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