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Abstract

The technique of ligand-exchange was investigated as a possible method for the extraction and concentration of organic compounds dissolved in seawater. Cation-exchange resins in transition metal forms were used to extract carboxylate anions and amino-acids from dilute solution in synthetic seawater. The optimum conditions found from small-scale experiments were applied to the extraction of ¹⁴C-labelled amino-acids from natural seawater. This work demonstrated (1) the strong bonding of transition-metal ions., especially Fe(iii), to the chelating resin Dowex A-1 (2) the sorption of citrate, tartrate, glycine and glutamate by Dowex A-1 in Fe(iii) form (3) the sorption of glutamate and alanine by the same resin in Ni(NH₃)₃. and Cu(NH₃) form (4) the displacement of the organic ligands by inorganic reagents: 2M KH₂PO₄ in the case of Fe(iii) and 30% ammonia in the case of Ni(NH₃)₃ and Cu(NH₃) forms. It was concluded that the method is of marginal utility for the first-stage extraction of organic ligands from seawater. The relationship of the experimental results to tabulated Stability Constants of Transition-metal complexes with organic ligands is briefly discussed.