Voltammogram, linear voltage-sweep

Figure 3.9 Linear voltage-sweep voltammogram with reversal of sweep direction to give a cyclic voltammogram. Initial sweep direction to more negative potential.

Fig. 11.4. Typical linear sweep voltammogram (LSV) data for the ICA film in background electrolyte LSV data is recorded (a) initially after film formation (b) after cycling and repeated holding first at a potential corresponding to complete oxidation (1 hour) and then at a potential for complete reduction of the film (1 hour) for an overall period of 2 days (c) same as (b) but for 5 days (d) in 0.1 M NaCI04 rather than 0.1 M LiCI04. The voltage sweep rate was 2.5 mV/s"1 in all cases.

For a linear sweep voltammogram, the applied voltage is a linear function of time, E= Ex + vt, where v = d El diis the sweep rate, in V s-1. We then use the macro SemiDifferentiate to find the corresponding shape of the linear sweep voltammogram. 

In its semi-integration mode, this macro takes the faradaic current of a linear sweep voltammogram, and transforms it into the underlying current- voltage curve corrected for the time-dependence of planar diffusion. The resulting curve is then amenable to further mathematical analysis along the lines pioneered by Koutecky, and summarized by, e.g., Heyrovsky ... 

Numerous excellent texts exist on the fundamentals of cyclic voltammetry. The reader is referred especially to the recent text by Bond, which provides an excellent treatment of fundamentals as well as applications. The important aspects of cyclic voltammetry are illustrated by the diagram shown in Figure 1 of a typical voltammogram of a soluble, reversible couple subjected to a linear potential sweep (and return scan) between applied voltages E and E2- The characteristic curve shown in Figure 1 provides peak potentials ( p and E° ) as well as peak currents 1° and Note that... 

The most popular electroanalytical technique used at solid electrodes is Cyclic Voltammetry (CV). In this technique, the applied potential is linearly cycled between two potentials, one below the standard potential of the species of interest and one above it (Fig. 7.12). In one half of the cycle the oxidized form of the species is reduced in the other half, it is reoxidized to its original form. The resulting current-voltage relationship (cyclic voltammogram) has a characteristic shape that depends on the kinetics of the electrochemical process, on the coupled chemical reactions, and on diffusion. The one shown in Fig. 7.12 corresponds to the reversible reduction of a soluble redox couple taking place at an electrode modified with a thick porous layer (Hurrell and Abruna, 1988). The peak current ip is directly proportional to the concentration of the electroactive species C (mM), to the volume V (pL) of the accumulation layer, and to the sweep rate v (mVs 1). 

In its semi-differentiation mode, the macro instead converts a stationary current-voltage curve into the corresponding linear sweep or cyclic voltammogram. 

Figure 3.18. Linear-sweep anodic-stripping voltammogram, 2 ppm Pb and 1 ppm Cu in 0.1 MHNO3. Conditions 5-minplating time at —1.10 V 15-sec rest time a thin-mercury-film electrode on glassy carbon and a voltage scan rate of 1 V/min for the strippir step.

Fig. 9. Linear sweep voltammetry (LSV) at the HMDE of samples of double-helical and thermally denatured DNAs at the concentration of 0.1 mg/ml. Medium 0.1 M sodium phosphate, pH 7.1. Voltage scan rate of 1.0 V/s, waiting time at the initial potential Uj was 60 s. (A) Voltammograms upper curves, samples of thermally denatured DNA, lower curves, samples of double-helical DNA initial potentials Uj are indicated in the lower parts of individual panels. (B) Dependence of LSV peak III height of the sample of double-helical (o) and thermally denatured (d) DNAs on initial potential Ej. In this article the value of x (see top curve at LFj = -0.4 V in the panel A) was taken to represent the height of LSV peak III.

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