Acomplexometric indicator is anionochromicdye that undergoes a definite color change in presence of specific metalions.[1] It forms a weakcomplex with the ions present in the solution, which has a significantly different color from the form existing outside the complex.Complexometric indicators are also known as pM indicators.[2]
Inanalytical chemistry, complexometric indicators are used incomplexometric titration to indicate the exact moment when all the metal ions in the solution are sequestered by achelating agent (most usuallyEDTA). Such indicators are also calledmetallochromic indicators.
The indicator may be present in another liquid phase in equilibrium with the titrated phase, the indicator is described asextraction indicator.
Some complexometric indicators are sensitive to air and are destroyed. When such solution loses color during titration, a drop or two of fresh indicator may have to be added.
Complexometric indicators are water-soluble organic molecules. Some examples are:
In some settings, when the titrated system is a redox system whose equilibrium is influenced by the removal of the metal ions, aredox indicator can function as a complexometric indicator.
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