ION-EXCHANGE MECHANISMS OF SOME TRANSITION-METALS ON A MIXED-BED RESIN WITH A COMPLEXING ELUENT

Ion-exchange chromatography was used for the simultaneous elution of t ransition metals. The mobile phase consisted of an acetate buffer with pyridine-2,6-dicarboxylic acid (PDCA) as a chelating agent; the stati onary phase was a mixed-bed resin that displays both anion- and cation -exchange properties. Under the selected conditions, the only species of the analyte that occur in solution are the anionic chelates M(PDCA) (2) while both the free cations and the chelates may be present in the resin. The mechanisms involved in this complex chromatographic patter n are described, considering either cation or anion exchange. It was f ound that the chromatographic behaviour of the transition metals can b e explained by electrostatic interactions, the prevailing mechanism be ing pure anion exchange. Selectivity coefficients between the eluted s pecies and either PDCA or acetate were derived from the experiments. T he results were compared with those obtained after replacement of the mixed-bed resin by a low capacity anion-exchange resin. In this case, additional mechanisms such as adsorption had to be taken into account in the explanation of the retention behaviour of the transition metals .