Complexometric titration (sometimes chelatometry) is a form of volumetric analysis in which the formation of a colored complex is used to indicate the end point of a titration. Complexometric titrations are particularly useful for the determination of a mixture of different metal ions in solution. An indicator

Complexometric indicator

A complexometric indicator is an ionochromic dye that undergoes a definite color change in presence of specific metal ions. It forms a weak complex with the ions present in the solution, which has a significantly different color from the form existing outside the complex.Complexometric indicators...

 capable of producing an unambiguous color change is usually used to detect the end-point of the titration.
In theory, any complexation reaction can be used as a volumetric technique provided that:

1. the reaction reaches equilibrium
   Chemical equilibrium
   In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...
   
    rapidly after each portion of titrant is added.
2. interfering situations do not arise.