AN NMR-STUDY ON THE ADSORPTION OF A METAL CHELATING AGENT AT A MICELLE WATER INTERFACE

The complexation of aqueous Zn2+ with a solvent extraction chelate, 7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline(K7HQ), in micellar solutions of n-dodecyloctaoxyethylene glycol monoether (C12E8) has been examined using an NMR technique. The ring resonance effect of the aromatic moiety of the K7HQ molecule has been used to determine the loci of solubilization of the free ligand and the metal complex in the host micelle. It has been found that the free ligand resides preferentially at the micelle core/water interface whereas the metal complex favors the more hydrophobic regions of the micelle core. The effect of pH on the loci of solubilization of the free ligand has also been studied. At low pH (1.4) the ligand carries a positive charge and its distribution is biased more to the micelle core/water interface than at higher pH (6), where it exists as a neutral zwitterionic species. The relevance of the micellar results to the extraction of metal ions from an aqueous phase into an organic phase are discussed. © 1993 by Academic Press, Inc.