Kinetic Studies on Metal Complexation Reactions by High-Performance Liquid Chromatography

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Equilibrium and kinetic studies on the ligand exchange reactions of 5-sulphoquinoline-8-ol (HQS) complexes of various metal ions with inorganic anions were carried out by high-performance liquid chromatography. The retention behavior of the metal complexes in reversed-phase ion-pair liquid chromatography was investigated by using an octadecyl-modified silica or a polystirene-divinylbenzene copolymer as a column packing and tetrabutylammonium ion as an ion pairing agent.1. The aluminum complex gave two or three peaks on the chromatograms whem eluents containing phosphate ion or fluoride ion were used, whereas the other metal complexes exhibited only one peak. In contrast with the results obtained with the phosphate or fluoride ion system, acetate and chloride ion eluent systems gave only one sharp peak for an injection of aluminum. It was elucidated that some of the aluminum peaks corresponded to mixed ligand complexes with HQS and phosphate ion or fluoride ion from the effects of the concentrations of HQS and these inorganic anions in the eluents on the areas of the peaks. The compositions of the mixed ligand complexes and the equilibrium constants of the ligand exchange reactions were also determined.2. The rate constants for the ligand exchange reactions described above were estimated from the relationship between the peak areas and the reaction time.3. The aluminum-HQS complex could completely be separated from the gallium complex by utilizing the ligand exchange reaction with fluoride ion.4. The kinetic studies on the ligand exchange reaction with reaction rates larger than that for the reactions described above has jist been started. It is also scheduled to clarify the mechanism of the, ligand exhange reaction of the aluminum-HQS complex.