Preconcentration of trace metal ions by combined complexation-anion exchange : Part I. Cobalt,zinc and cadmium with 2-(3′-sulfobenzoyl)-pyridine-2-pyridylhydrazone

The ligand 2-(3′-sulfobenzoyl)pyridine-2-pyridylhydrazone forms anionic complexes with Fe, Co, Ni, Cu, Zn, Cd, Hg and Pd which demonstrate high affinities for anion-exchange resins. The behavior of Co, Zn and Cd was studied in detail, with respect to pH, flow rate, ligand/metal ratio, volume, concentration and percentage retention of the anionic complex on the Bio-Rad AG1-X2 resin. At optimal conditions, Co, Zn and Cd are quantitatively retained; Zn and Cd are removed completely by 2 M HNO₃ or 1 M H₂SO₄, and Co by 12 M HCl and 1 M HNO₃. Concentration enhancements up to 300-fold can be easily achieved. The complexes can be left on the columns for 48–96 h and still be quantitatively recovered. A ligand-loaded resin column can also be used to remove Co, Zn and Cd from solution. Batch experiments were used to determine distribution coefficients for the metal complexes.