Describe the alternating current methods in voltammetry
Alternative current (AC) voltammetry is an accurate electroanalysis method and combination with preconcentration will enhance the sensitivities of this analytical techniques. AC Voltammetry generally involves in the application of a sinusodially oscillating voltage to an electrochemical cell. The AC experiment is used in conjunction with a fixed amplifier or frequency analyser which will increase sensitivity considerably over the early described techniques. AC voltammetry can also reveal the important of mechanistic and kinetic information which is not easily available when using the tradition voltammetric techniques.
Measurement of AC voltammetric is usually used in an electrochemical cell and the dominate mode of transport is diffusion. A steady DC signal or voltage sweep will often combined with the AC voltage.
The following figure shows a cyclic voltammetric signal with an AC perturbation.
Alternating potential usually has a frequency of 50-100Hz and 10-20mV amplitude. The AC signal causes a perturbation in the surface concentration and DC potential ramp maintained the concentration. The resulting AC current is plotted against the potential. For example, voltammogram appears a peak, the potential of which is the same as the polarographic half-wave potential. At this region, the sinusoid has maximum impact on the surface concentration like on the current.
For a reversible system, such a response is actually the derivative of the DC polarographic response. The concentration of the analyte is proportional to the height of the AC voltammetric peak and for a reversible reaction to the square root of the frequency (ω), the term
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