Comparative electrolytic analysis, polarographic analysis and voltammetric analysis

In polarographic analysis, mercury dropping electrode is usually used as cathode. In the process of electrolysis, the surface area of mercury electrode is very small and the current density is quite high, but the concentration of reducible substances near it tends to zero, so there is a polarization concentration difference, which shows that the diffusion current is proportional to the concentration of reducible substances. This is the basis of polarographic analysis. Because different substances have different reduction potentials, polarography uses this for qualitative analysis. The reduction potential of a substance is not fixed, but it can change slightly with the concentration of the substance, so polarography is based on their half-wave potential which does not change with the concentration.