Reaction influence peak height

Fig. 7.31 Influence of frequency on the peak height of square wave voltammograms of a two-electron electrochemical reaction at disc (solid line) and (hemi)spherical (dashed line)...

When both redox reactions are sluggish, both SWV and SWVC responses become very complex because they are influenced by both the kinetic and thermodynamic parameters of the electrode reactions and those associated with the square wave waveform (i.e., Sw> / and A s). Basically, when two peaks are observed, their peak heights are determined mainly by the magnitude of the dimensionless kinetic... 

The parent peak height of CIF declined according to a (pseudo) first-order decay. However, the appearance and influence of CI2 upon the rate led to the proposition that the mechanism for the decomposition was complex and that the first-order rate coefficients were apparent. The absence of Fj in the mass spectra eliminated the importance of the F atom abstraction reaction and subsequent decomposition of F2. The results were accounted for by the steps... 

Although the described spectroscopic methods for quantitative in-line analysis can in principle be applied to all kinds of screening experiments that comprise systematic variations of process parameters, this approach has to be handled with care since some of the parameters have an undesired non-linear effect on a spectrum. For instance, in NIR spectroscopy, an increase in temperature can cause band shifts and influence the peak height. Variations in stoichiometry, which can be easily achieved in a microreaction process by changing the reactant flows, have a direct impact on the analyzed compound concentration. However, such modifications can be calculated subsequent to the reaction, if concentrations are in the linear detection range or the detection range was calibrated in advance. 

The influence of the reversibility of the electrochemical reaction on the SW net charge-potential curves ( (Gsw/Gf) - (Eindex is plotted in Fig. 7.48 for different values of the square wave amplitude ( sw = 25,50,100, and 150mV) and three values of the dimensionless surface rate constant (1° ( k°t) = 10,0.25, and 0.01), which correspond to reversible, quasi-reversible, and fully irreversible behaviors. Thus, it can be seen that for a reversible process (Fig. 7.48a), the (Gsw/Gf) — (Eindex EL°) curves present a well-defined peak centered at the formal potential (dotted line), whose height and half-peak width increase with Esw (in line with Eqs. (7.118) and (7.119)), until, for sw > lOOmV, the peak becomes a broad plateau whose height coincides with Q s. This behavior can also be observed for the quasi-reversible case shown in Fig. 7.48b, although in this case, there is a smaller increase of the net charge curves with sw, and the plateau is not obtained for the values of sw used, with a higher square wave amplitude needed to obtain it. Nevertheless, even for this low value of the dimensionless rate constant, the peak potential of the SWVC curves coincides with the formal potential. This coincidence can be observed for values of sw > 10 mV. 

Control electrodes incubated in hydrogen peroxide without styrene showed catalytic oxidation peaks of similar heights to freshly prepared films (Fig. 9). Thus the low concentrations of hydrogen peroxide used had no measurable influence on ds-DNA. Only peaks for films that had been activated by hydrogen peroxide and styrene together increased with reaction time. 

The presence of other cathodic and anodic peaks points to electrochemical activity on other oxygen species existing on the carbon surface (see Table 4). Additionally, they may be overlapped by a significant capacitive current [153]. However, it should be remembered that the real chemical structure of an oxidized carbon surface [101] depends on the hydrolysis of lactone-, ester- or ether-like anhydrous systems and the ionization of some functionalities at extreme pH values (acidic or basic environments) [91]. These phenomena influence the surface density of species that can take part in charge-transfer processes, which explains the observed differences in height of reduction peak in different environments (see Fig. 18). These relationships can account for the reactions, e.g. [7,14,148],... 

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