Polarograms

Polarograms are graphs produced in polarography, a form of electrochemical analysis in which the current flowing through an electrochemical cell is recorded as a function of the applied potential. The resulting plot, typically current (I) versus potential (E), reflects the redox behavior of species present in solution and is used to extract information about their identity and concentration.

The method was developed in the mid-20th century by Jaroslav Heyrovský, who technologyized the use of the dropping mercury electrode as the working electrode. In a polarographic setup, a solution containing a supporting electrolyte and the analyte is subjected to a controlled potential sweep. As the potential passes the reduction or oxidation threshold of each species, a characteristic wave in the current appears. The waves rise to a diffusion-limited plateau, and the features of the waves—such as the half-wave potential and the limiting current—provide quantitative and qualitative information about the analyte.

Key features of polarograms include the appearance of one or more waves corresponding to reducible or oxidizable species, the plateau current indicating diffusion control, and the half-wave (or half-peak) potential that relates to the formal redox potential of the species. The height of each wave is proportional to the concentration within a suitable linear range, enabling quantitative analysis.

Applications of polarograms span trace metal analysis, organic and inorganic redox studies, and the identification of electroactive species in complex mixtures. Limitations include the use of mercury electrodes, potential interference from adsorbed species, and practical constraints on simultaneous multi-species determination. The technique remains foundational in electroanalytical chemistry, with polarograms guiding interpretation of more modern voltammetric methods.