A STUDY OF MIXED - METAL HYDROXYCARBOXYLIC ACID COMPLEXES OF CHROMIUM AND INDIUM WITH CITRATE BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY AND ISOTACHOPHORESIS

The study of mixed metal complexes of hydroxycarboxylic acids is of fundamental importance to solvent extraction and ion exchange separations. In this work a mixed-metal complex of chromium-indium with citric acid complexing reagent was investigated.; A study of potentiometric pH titrations of citric acid, in the presence of vanadium (II) and/or cupric metal ions was conducted to establish the participation of the hydroxyl functional group on citric acid in complex formation with the metal ions.; Preliminary to a study of mixed-metal complexes of Cr(III), M(II) or M(III), and citric acid, a chromatographic study of the Cr(III), citric acid system was undertaken. Separation on small particle polystyrene resins showed the chromium citrate species to be negatively charged. The improved resolving power and exchange kinetics of an amino bonded packings as compared to polystyrene resins packing, revealed a simple equimolar mixture of Cr(III) perchlorate and citric acid on reaction gives rise to ten to fifteen solutions species. Such a product distribution was not suspected by previous workers. This result has been confirmed by the isotachophoretic separation of the same reaction mixtures.; A systematic study of the effects of concentration and pH on the yields of individual complexes was carried out. The later eluting peaks are favoured by increasing concentration of the reactants and by increasing pH of the reaction medium. Through the incorporation of ('51)Cr(III) and ('14)C-labelled citric acid in the reaction mixture, the chromium/citrate ratios of some of the major peaks could be established. Based on these observations the structures of some of the complexes are postulated.; An instrument was designed and constructed to carry out isotachophoresis separations. When applied to the chromium-citrate and chromium-indium-citrate systems, separations completely analogous to those using chromatography were obtained. Differential pulse polarography was also used on the indium complexes to obtain confirmatory evidence.