SILVER SELECTIVITY - A STUDY OF METAL RECOGNITION IN SINGLE AND MULTIPLE PHASES

Thiaalkane-bridge bis(benzimidazoles) varying both in the nature of the bridge and in the pendant groups attached to secondary nitrogen have been synthesised to assess metal selectivity in single and multiple phases. The single-phase studies (H-1 NMR, fast atom bombardment mass spectroscopy) and molecular modelling were intended primarily to rationalise the trends observed in the multiple-phase (bulk liquid-membrane) experiments. Selectivity for silver ion was studied by all of these techniques, whilst the membrane experiments were extended to assess selectivity for cadmium, zinc, lead and copper ions. All of these metal salts (as nitrates) were assessed in the membrane experiments or in pairwise competition experiments. Some useful separations were effected, the most striking being that for silver ions over lead. The lack of comparison amongst the results from the methods chosen indicates that a full understanding of the complex kinetics of three-phase transport is still to be attained.