Argentimetric

Argentimetric, or argentimetric titration, is a class of quantitative chemical analysis methods in which silver ions (Ag+) are used as the titrant in a precipitation titration. The technique is primarily applied to determine halide ions such as chloride (Cl−), bromide (Br−), and iodide (I−), and in some cases other species that form insoluble silver salts.

Principle: The sample is acidified and treated with standardized AgNO3. Halide ions react to form insoluble silver halides (AgCl, AgBr, AgI). The endpoint is detected by an indicator that reveals the presence of free Ag+ once all halide has been precipitated. The classical Mohr method uses potassium chromate (CrO4^2−) as an adsorption indicator; at the endpoint, silver chromate (Ag2CrO4) precipitates, producing a brick-red color. Other variants use adsorption indicators (Fajans methods), potentiometric detection, or instrumental methods for endpoint determination.

Procedure and applications: In water analysis, argentimetric titration is widely used to determine chloride content in drinking water, wastewater, and foods; similar procedures can quantify bromide and iodide in various samples. Back-titration or masking steps may be employed when the sample contains complexing agents or interfering constituents.

Advantages and limitations: The method is simple, inexpensive, and does not require sophisticated equipment. Interferences include complexation of Ag+ by ammonia, cyanide, thiocyanate, or organic ligands; the presence of competing precipitates or strong buffers can affect accuracy; sample acidity must be controlled.

History and terminology: The method is associated with the Mohr titration for chloride, developed in the 19th century, and is part of the broader field of argentometry, the use of silver salts in titrations. The term argentimetric derives from the Latin argentum, silver.