Electrochemical Methods of Analysis

the aggregate of methods of qualitative and quantitative analysis based on electrochemical phenomena occurring within a medium or at the phase boundary and related to changes in the structure, chemical composition, or concentration of the compound being analyzed. These methods are divided into five major groups: potentiometry, voltammetry, coulometry, conductometry, and dielectrometry.

Potentiometry combines methods based on the measurement of the emf of reversible electrochemical circuits, when the potential of the working electrode is close to the equilibrium value (see). This method includes redox titration (seeOXIDIMETRY), ionometry, and potentiometric titration.

Voltammetry is based on the study of the dependence of polarization current on the voltage applied to an electrochemical cell when the potential of the working electrode differs significantly from the equilibrium value (seePOLARIZATION, ELECTROCHEMICAL). Voltammetry, with its variety of methods, constitutes the largest group of electrochemical methods of analysis and is commonly used for the determination of compounds in solutions and melts (for example, polarography and amperometry). (SeePOLAROGRAPHY.)

Coulometry combines methods of analysis based on the measurement of the amount of material deposited on an electrode in the course of an electrochemical reaction in accordance with Faraday’s laws. In coulometry, the potential of the working electrode differs from the equilibrium value. A distinction is made between coulometry at constant potential and coulometry at constant current. The latter includes both direct and indirect methods, electroanalysis, and coulometric titration.

Conductometry encompasses methods in which the electrical conductivity of electrolytes (aqueous and nonaqueous solutions, colloid systems, melts, and solids) is measured (seeELECTRICAL CONDUCTIVITY OF ELECTROLYTES). It is based on the change in the concentration of a compound or the chemical composition of a medium in the interelectrode space; it is not linked with the electrode potential, which is usually close to the equilibrium value. Conductometry includes both direct analytical methods (used, for example, in salinometers) and indirect analytical methods (for example, in gas analysis) using either direct or alternating current (low-or high-frequency current). It also includes chrono-conductometry and low-frequency and high-frequency titration. (SeeGAS ANALYSIS.)

Dielectrometry combines analytical methods based on the measurement of the dielectric constant of a substance resulting from the orientation of particles (molecules or ions) that have a dipole moment in an electric field. These methods are used to monitor the purity of dielectrics, for example, to detect small amounts of moisture. Dielectrometric titration is used to analyze solutions.