ROLE OF LIGAND PURITY IN SEPARATIONS OF ALKALINE-EARTH METALS AS ARSENAZO-I COMPLEXES BY CAPILLARY-ZONE-ELECTROPHORESIS

In the separation of metal ions by capillary electrophoresis in the fo rm of kinetically labile complexes formed through the incorporation of an auxiliary complexing ligand into the background electrolyte (BGE), it has been shown that the purity of this auxiliary complexing ligand can play a crucial role in the selectivity and efficiency of the resu ltant separations. Using the separation of alkaline earth metals as co mplexes with the metallochromic ligand arsenate I as a model system, t he effects of the addition of low concentrations of simulated impuriti es, in the form of various metal ions and competing ligands, were stud ied, Additions of Fe-III at low micromolar levels to a BGE containing 1 mM arsenate I resulted in severe peak tailing. The addition of the c ompeting ligands diethylenetriaminepentaacetic acid (DTPA) or arsenate III, at a molar ratio as low as 1:1000 to arsenate I, also caused sub stantial peak broadening and altered the separation selectivity. The p ractical implications of the above results for the separation of metal s as labile complexes, using capillary zone electrophoresis (CZE) syst ems similar to the above, are discussed. (C) 1998 Elsevier Science B.V .