Voltammetric techniques, classical

Voltammetric techniques that can be applied in the stripping step are staircase, pulse, differential pulse, and square-wave voltammetry. Each of them has been described in detail in previous chapters. Their common characteristic is a bell-shaped form of the response caused by the definite amount of accumulated substance. Staircase voltammetry is provided by computer-controlled instruments as a substitution for the classical linear scan voltammetry [102]. Normal pulse stripping voltammetry is sometimes called reverse pulse voltammetry. Its favorable property is the re-plating of the electroactive substance in between the pulses [103]. Differential pulse voltammetry has the most rigorously discriminating capacitive current, whereas square-wave voltammetry is the fastest stripping technique. All four techniques are insensitive to fast and reversible surface reactions in which both the reactant and product are immobilized on the electrode surface [104,105]. In all techniques mentioned above, the maximum response, or the peak current, depends linearly on the surface, or volume, concentration of the accumulated substance. The factor of this linear proportionality is the amperometric constant of the voltammetric technique. It determines the sensitivity of the method. The lowest detectable concentration of the analyte depends on the smallest peak current that can be reliably measured and on the efficacy of accumulation. For instance, in linear scan voltammetry of the reversible surface reaction i ads + ne Pads, the peak current is [52]... 

Controlled potential methods have been successfully applied to ion-selective electrodes. The term voltammetric ion-selective electrode (VISE) was suggested by Cammann [60], Senda and coworkers called electrodes placed under constant potential conditions amperometric ion-selective electrodes (AISE) [61, 62], Similarly to controlled current methods potentiostatic techniques help to overcome two major drawbacks of classic potentiometry. First, ISEs have a logarithmic response function, which makes them less sensitive to the small change in activity of the detected analyte. Second, an increased charge of the detected ions leads to the reduction of the response slope and, therefore, to the loss of sensitivity, especially in the case of large polyionic molecules. Due to the underlying response mechanism voltammetric ISEs yield a linear response function that is not as sensitive to the charge of the ion. 

The small area of a microelectrode, with its proportionately low capacitance, allows its use at very short time scales compared to the time scale used with a classical voltammetric electrode. As we have seen earlier in this chapter, when microelectrodes are used at short time scales, the current follows the behavior expected for diffusion in one dimension. Thus, the development of high-speed voltammetric methods with microelectrodes was a logical step, and has greatly expanded the scope and capabilities of electrochemical techniques [41]. Rapid electrochemical methods allow evaluation of the larger rate constants of rapid heterogeneous and/or homogeneous reactions. For example, theories of hetero-... 

A wide variety of the experimental technique is available for the study of sorption phenomena and for the characterization of surface structure and state via sorption phenomena. Although the classical electrochemical methods—galvanostatic, potentiostatic, potentiodynamic (voltammetric, cyclicvoltammetric) and transient—are widely used, new methods were coming into foreground during the last two decades. The main cheir-acteristic of the new experimental methods is the simultaneous use (coupling) of electrochemical techniques with other nonelectrochemical methods. 

Classically amperometry has been concerned with the maintenance of a fixed potential between two electrodes. More recently, pulsed techniques have come to the fore some details of these are included in Table 8.3. The applied potential at which the current measurement is made is usually selected to correspond to the mass transport limited portion of the corresponding voltammetric scan. Theoretically, in a quiescent solution, this is electrochemical suicide. The current ii obtained at conventional electrodes under such circumstances gradually decays to zero according to the Cottrell equation (4) ... 

The voltammetric behavior of PB films is characterized by the presence of two prominent reversible peaks. This is shown in Figure 18. The nature of the redox processes associated with the electrochromic effect have been investigated using in situ Mossbauer spectroscopy by Itaya and coworkers/ in what may be regarded as a classical example of the use of this technique in the study of electrochemical systems. 

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