The familiar colour reactions given
by metal ions with a number of ligands (especially chelating ligands),
as a result of formation of coordination entities, form the basis for
their detection and estimation by classical and instrumental methods
of analysis Examples of such reagents include EDTA, DMG
(dimethylglyoxime), a–nitroso–b–naphthol, cupron, etc •
Hardness of water is estimated by simple titration with Na2EDTA The Ca
2+ and Mg
2+ ions form stable complexes with EDTA