In theory, any complexation reaction can be used as a volumetric technique provided that:
# The reaction reaches equilibrium rapidly after each portion of titrant is added.
# Interfering situations do not arise.  For instance, the stepwise formation of several different complexes of the metal ion with the titrant, resulting in the presence of more than one complex in solution during the titration process.
# A complexometric indicator capable of locating equivalence point with fair  accuracy is available.
In practice, the use of EDTA as a titrant is well established.