polarografi

Polarografi is an electroanalytical technique in which a working electrode, traditionally a dropping mercury electrode (DME), is subjected to a swept or stepped potential while the resulting current is recorded. The current–potential relationship obtained is called a polarogram and reflects the electrochemical behavior of the analyte at the electrode surface.

Principle and key features: As the potential is varied, species in solution are reduced or oxidized at the electrode, and the measured current increases to a diffusion-limited plateau. The plateau current, Ilim, is related to the analyte concentration, while the half-wave potential, E1/2, is characteristic of the redox couple. The method relies on diffusion-controlled mass transport to the renewable mercury surface, producing well-defined waves that facilitate qualitative and quantitative analysis.

History and development: Polarografi was developed in the early to mid-20th century by Jaroslav Heyrovský, who established the technique and the instrumentation for recording polarograms. The method earned Heyrovský the Nobel Prize in Chemistry in 1959.

Procedure and instrumentation: Typical setups employ three electrodes: a dropping mercury working electrode, a reference electrode (such as Ag/AgCl or calomel), and a platinum counter electrode. A programmable voltage sweep or step is applied, and the current is monitored. The DME provides a fresh surface with low background current, enabling sensitive measurements across a range of inorganic and organic analytes.

Applications and status: Polarography has been widely used for trace analysis of metal ions, halides, and organic compounds in environmental, pharmaceutical, and clinical samples. While modern voltammetric techniques (e.g., differential pulse and square-wave voltammetry) have largely supplanted polarography due to environmental concerns with mercury and improved capabilities, polarography remains a foundational method in electrochemistry.