EDTA, also known as a chelating agent, can form coordination complexes with metal ions through several donor atoms in its structure. This results in the formation of stable metal-EDTA complexes with a 1:1 stoichiometry. During complexometric titrations, EDTA acts as the titrant, while the metal ion of interest present in the analyte solution is the analyte.
The endpoint of the titration is usually detected using an indicator that undergoes a distinct color change in the presence of excess EDTA. An example of such an indicator is Eriochrome Black T, which changes from red to blue when all the metal ions have been complexed by EDTA.
Complexometric titrations using tetrasodium salt of EDTA are useful for determining the concentration of metal ions in solutions, quantifying the amounts of specific metals in mixtures, and investigating the chemical speciation of metal complexes.
