Anion exchange separation of calcium from magnesium or strontium using ethyleneglycol-bis (2-aminoethylether) tetraacetic acid (EGTA)

The large difference between the stability constants of Ca-EGTA and Mg-EGTA or Sr-EGTA complexes was used for the selective sorption and separation of calcium with anion exchangers. The distribution coefficients of EGTA and its metal complexes mentioned were estimated on three types of anion exchangers with different basicity and different crosslinking of the resin matrix. The calcium EGTA complex can be selectively adsorbed on the anion exchange resin from a solution pH 6.0-6.5 while magnesium (at pH 5.9-6.1 also strontium) is not sorbed under these conditions. No quantitative separation of calcium was observed if large amount of other anions was present in the sample solution. (author)