Polarography - Polarographic analysis techniques

Polarography, named after its Nobel Prize-winning inventor J. Heyrovsky, is at the origin of a large number of electroanalytical techniques, including voltammetry. Voltammetry is an analytical method that involves the electrochemical study of electroactive (or non-electroactive) compounds in solution, using a mercury drop indicator electrode. It differs from its descendant, voltammetry, essentially in the nature of the electrode, since the methodologies are often identical. The specific features of the mercury drop electrode compared to solid conductive electrodes stem from the particular properties of this metal which, being liquid at room temperature, allows renewal of the electrode's active surface, easily leads to the formation of a number of amalgams with metals, and enables reductions to very negative potentials (reductions impossible to achieve on platinum or glassy carbon electrodes). In oxidation, on the other hand, the exploration of potentials in polarography is limited by the oxidation of mercury, which explains why a large proportion of applications have concerned electroreducible compounds. This range of exploration potentials is naturally influenced by the pH, the supporting electrolyte or the solvent, which can limit this range. Another important advantage of mercury is that each drop corresponds to a new electrode, geometrically identical to the previous one, but with no memory of the electrochemical phenomenon that affected the previous drops.

These remarks are enough to underline the interest of such an electrode in electroanalysis, as can be seen from the scientific work on polarography, which has grown steadily since the origins of the method.

The term "polarography" will be extended here to techniques using a mercury electrode as an indicator electrode: dropping or hanging mercury drops, but also thin mercury films (on solid electrodes).

Polarography encompasses a number of analytical techniques covering a wide range of concentrations, from classical polarography (10 ^–3 to 10 ^–5 mol · L ^–1 ), to redissolution methods (suitable for traces and ultratraces) and pulse methods (10 ^–4 to 10 ^–8 mol · L ^–1 ). Most of these polarographic techniques can be applied with today's equipment. They can be applied to a wide range of inorganic, organic, organometallic and biological substances in a large number of industrial and research sectors.

This octogenarian technique had its heyday in the last century, from the 1960s to the 1980s. Since...