5.2 : Complexometric Titration: Ligands

Different monodentate and polydentate ligands are used as complexing agents in complexometric titration reactions. The formation of complexes by mono- and bidentate ligands involves two or more intermediate steps, limiting their use as complexing agents. In comparison, polydentate ligands can form complexes with metal ions in a single-step process, facilitating sharper end points. This means polydentate ligands, such as amino carboxylic acid derivatives, are most commonly employed in complexometric titrations. These ligands can form stable chelates with metal ions via carboxylate oxygens and amine nitrogens. Among the amino carboxylic acid derivatives, ethylenediaminetetraacetic acid (EDTA) is the most widely used complexing agent.

Complexometric titrations are used to quantify most metals. Quantitative determination of the total hardness of water and the investigation of calcium in the blood are two such applications of complexometric titration.