EDTA: Directe, Back- en Displacement-titratie

EDTA titration includes direct, back, displacement, indirect, and alkalimetric titration.

In a direct titration, a metal ion solution is directly titrated with EDTA—for example, a lead(II) ion solution is buffered at pH 10, with tartrate already present to prevent lead(II) hydroxide precipitation.

This solution is directly titrated with standard EDTA until the end point is reached.

However, some metal ions react too slowly or block the indicators, and some precipitate without EDTA. So, a known excess of EDTA solution is added and back-titrated with a second metal ion.

For example, after mixing an aluminum ion solution with excess EDTA, the remaining EDTA is back-titrated with a visual indicator and a standard zinc ion solution to reach the end point.

For metal ions that don't have a good indicator, displacement titration can be used.

For instance, titration of calcium ions with an excess magnesium–EDTA solution displaces magnesium to form a stable calcium–EDTA complex. The displaced magnesium ions are titrated with standard EDTA to reach the end point.