Ligand-exchange separation of amino acids. II. Influence of the eluent composition and of the nature of the ion exchanger.

The ligand-exchange separation of amino acids in protein hydrolysates has been studied in ammoniacal media. The various factors influencing the chromatographic behaviour have been investigated. The selectivity of the process and the column efficiency depend appreciably on the resin matrix and the nature of the functional groups. The best results have been obtained with the acrylic-type Bio Rex 70 resin, in the copper(II) form. The zinc(II) form of this support has also been tested; the elution order of glycine, alanine and leucine is the same as with the copper(II) form, but the affinities of these molecules for the zinc(II) resin are weaker. The influence of the concentrations of copper(II) and ammonia on the elution volumes obtained for all the amino acids with the copper(II) Bio Rex 70 resin has been studied. The general variation of retention and selectivity with eluent composition confirms the theoretical expressions established previously. Ligand-exchange chromatography has been compared to the conventional ion-exchange process using acidic or basic species. This study reveals analogies and differences between both techniques, and shows that ligand exchange can provide new opportunities for the separation of amino acids.