Principle of polarography

The basic apparatus of polarography is shown in Figure 1. The polarizing electrode (mercuric drop electrode) is usually connected to the negative end of the polarizing voltage, and the reference electrode (calomel electrode) is connected to the positive end of the polarizing voltage. When the applied DC voltage on the two electrodes reaches a decomposition voltage sufficient to make the measured electroactive substances in the drop of mercury electrode reduction before the current through the electrolytic cell has been very small (this small current is called the residual current), to reach the decomposition voltage, the measured substances began to drop of mercury electrode reduction, resulting in the polar spectrum of the current, and thereafter the polar spectrum of the current with the increase in the applied voltage and increase dramatically and gradually reach the limiting value (limit current), and no longer with the applied voltage, the polar spectrum of the electrolytic cell. Current), no longer with the increase in applied voltage and increase. The current-voltage curve obtained in this way is called the polar wave. The half-wave potential E1/2 of the polar wave is a characteristic value of the substance to be measured and can be used for qualitative analysis. The diffusion current depends on the speed of diffusion of the measured substance from the solution body to the surface of the mercury drop electrode, the size of which is determined by the concentration of the measured substance in the solution, according to which quantitative analysis can be carried out.