Peak height differential pulse polarography

When DC polarography is applied to phenobarbital, the wave is indistinct. However, when differential-pulse polarography is used, easily measurable peaks corresponding to mercury-salt formation are obtained, the total height of which is a linear function of concentration. This procedure has been successfully applied to the determination of phenobarbital in the presence of a number of other drugs in studies of drug metabolism. 

The potential of the peak Ep is indicative of which species is involved. If the reduction (or oxidation) mechanism is diffusion-controlled the concentration of the species controls the Faradaic current. Since differential pulse polarography effectively displays the derivative of this current, theoretically it is the area under the peak which is proportional to the concentration. However, provided the shape of the peak does not change, the height of the peak is also proportional to concentration. The choice between the two modes of measurement will be discussed later. 

Differential pulse polarography is particulary susceptible to surface active phenomena. Adsorbed forms of the analyte and its electrode products can give rise to separate peaks. But even the adsorption of otherwise inactive third species can alter the reversibility and electrode kinetics of the process producing sometimes huge changes in the shape of peak. The area under the peak will, however, remain constant in most cases. But the height of the peak is of no use. If surfactants are likely to be present it is best to calibrate and measure the area under the peak. 

As in differential pulse polarography, the characteristic parameters of the AC wave are the peak height, Ip,Ac the peak potential, Ep ac and the half-peak width, Wi/2-... 

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