Coulometric

Coulometric is a class of electrochemical methods in which the quantity of a substance is determined by measuring the total electric charge passed during its electrolytic transformation. The approach rests on Faraday's laws, n = Q/(zF), where n is the amount of substance in moles, Q is total electric charge in coulombs, z is the number of electrons involved per molecule, and F is the Faraday constant (approximately 96485 C/mol).

Two main branches are galvanostatic (constant-current) coulometry and coulometric titration. In galvanostatic coulometry, a fixed current is applied to completely convert the analyte at an electrode; the charge required to reach completion yields the amount of substance. In coulometric titration, a titrant is generated electrochemically at an electrode and added to react with the analyte until the end point is reached, allowing absolute quantification without external reagents.

Common applications include determination of water content (Karl Fischer coulometry), determination of oxidants or reductants in inorganic and organic samples, and trace analysis of metals or other ions. Advantages include high accuracy, direct traceability to fundamental constants, and minimal chemical reagents. Limitations include the need for complete, selective reaction, potential side reactions, diffusion limitations, and the requirement to know or control the stoichiometry.

Historically, coulometry has been part of the development of quantitative electrochemistry since the 19th century and remains a standard technique in analytical chemistry.