Complex or Metal Indicators

Complex or metal indicators are organic materials that are capable of forming colored complexes with metal ions. In this, the free indicator has a different color to that of the complexed form. For the detection of the end-point of a complexometric titration, it is essential to use one of the metal indicators that form complexes with metal ions which differ in color from the indicators themselves. In addition, the reagent properties must be suited to the sensitivity and the acid-base characteristics of the indicator. Complex or metal indicators are used, for example, in the volumetric analytical determination of the concentration of metal ions, e.g. in complexometric titrations. Determination of water hardness is a
common application.