Control of Adsorption/Desorption of Anions Based on Redox of Solid Phase Coated with Cobalt Complexes

Abstract

The adsorption-desorption behaviors of hydrophobic anion on the solid phase coated with redox-active metal complexes (ML₂^+/0 ; M, Co^III/II ; L⁻, pyridylazo compounds) were investigated. The combination of a cobalt complex of poly vinyl phenol introduced with a 2-pyridylazo group and a solid-phase extraction cartridge packed with styrene-divinyl benzene copolymer sorbent showed the highest adsorption capacity for methyl orange as a hydrophobic anion. The percentage adsorption of methyl orange (1.0 μmol) on this solid phase was more than 99%, even in the presence of a 100-fold stoichiometric excess of coexisting anions (ClO₄⁻, Cl⁻). Methyl orange molecules were desorbed by reducing the cobalt complexes in the solid phase with a 1.0 × 10⁻² M ascorbic acid solution.