Complexometric

Complexometric refers to methods that rely on complex formation between metal ions and ligands for measurement or analysis. In analytical chemistry, complexometric titration is a common technique in which a chelating agent binds metal ions to form stable soluble complexes, allowing quantification of the target metals. The most widely used titrant is ethylenediaminetetraacetic acid (EDTA) or related chelators. The method depends on the high formation constants of metal–ligand complexes and on the stoichiometry of the metal–titrant interaction, often 1:1 but in some cases different ratios apply.

Endpoint detection in complexometric titrations is typically achieved with a metallochromic indicator that changes color when free metal ions disappear, or with instrumental methods such as potentiometry or spectrophotometry. The pH of the solution and appropriate buffering are important because EDTA binding varies with pH, and different metals are best complexed at different pH values. Sample preparation may include masking interfering ions or selecting a buffer that optimizes selectivity for the target metal.

Applications of complexometric methods cover a wide range of metals and matrices. They are used to determine calcium and magnesium hardness in water, trace metals in environmental samples, and metal contents in foods, pharmaceuticals, alloys, and biological specimens. The approach offers advantages such as broad applicability, relatively high selectivity, and compatibility with complex matrices. Limitations include interference from other ligands that compete for EDTA or bind the target metal, reliance on careful pH control, and the need for accurate standardization of the EDTA solution and appropriate indicators or instruments.