I am interested in purifying tin (about 50 ug) from a mixture of tin, cadmium (about 1 g) and copper(about 0.1 g). The method a customer has provided is as follows:

Preparation of the mixture for elution involves oxidation with HNO3/H2O2 and then dissolution in 9 N HCl, so it is likely that the moieties present are SnCl4, CdCl2, CuCl2, and their complex anions. A Bio-Rad AG1-X4 column is prepared in 9 N HCl saturated with sodium bromate, followed by adding the mixture, dissolved in 9 N HCl to the column; and eluting with 0.1 N HNO3. In this process, Cu comes off rather quickly, followed by the Sn, which comes off bimodally: a large band followed by a smaller band which tails. Cd comes off last, usually overlapping the tailing Sn band. My conjecture is that the first Sn band is Sn(IV) and the latter band Sn(II). Presumably, the bromate is there to maintain the Sn(IV) oxidation state, though perhaps it also aids in the separation. Is anyone familiar with this separation technique (bromated anion exchange column, HCl/HNO3 system)? If so, is there something I can do to eliminate the Sn(II) and/or reduce the tailing? Is there a better system for doing this separation?