Selective edta titration of gallium or aluminium in the presence of other metals

The selective determination of aluminium or gallium by EDTA titration is reported. Gallium or aluminium is titrated together with other multivalent ions with EDTA at pH 3-7 and then the pH is raised above 10.5. Aluminates or galliumates are formed with the consequent release of EDTA from the EDTA complexes. The released EDTA is titrated with lead solution using Xylenol Orange as an indicator and with copper using photometric detection of the end-point, for the determination of gallium and aluminium respectively. The theoretical basis of the procedure is discussed.