10.17 : Voltammetry: Overview

Voltammetry is an electroanalytical technique in which the current flowing through an electrochemical cell is measured as a function of applied potential, typically under conditions of concentration polarization. The technique provides valuable information about redox-active species, and the current response is plotted as a voltammogram.

A voltammetric cell uses three electrodes: a working electrode, a reference electrode, and an auxiliary electrode. The redox reactions occur in the working electrode, and a potentiostat controls its potential. Mercury electrodes are frequently used as working electrodes due to their wide negative potential range, which minimizes interference from hydrogen evolution. Mercury electrodes can form amalgams with various metals, enhancing certain redox reactions. In addition, their surface can be renewed by forming new drops, maintaining accuracy. Common types include the hanging mercury drop electrode (HMDE) and the dropping mercury electrode (DME).

The reference electrode, such as the saturated calomel electrode or silver-silver chloride electrode, plays a crucial role in voltammetry. It maintains a constant potential, ensuring accurate measurement. The auxiliary electrode, often a platinum wire, completes the circuit.

Mercury electrodes are preferred in many applications due to their large negative potential range, which prevents unwanted hydrogen reduction, and their ability to form amalgams. Their versatility and the ability to renew the electrode surface ensure consistent and reliable results during measurements.

Voltammetry is widely applied in environmental monitoring (e.g., detecting trace metals), pharmaceutical analysis, and electrochemical sensor development. By analyzing the current response, voltammetry helps determine the concentration of electroactive analytes in the solution. In dilute solutions, the current reaches a limiting value directly proportional to the analyte's concentration, making this technique highly valuable for quantitative analysis.