Ion chromatography using a charged complex anion-exchange group Original Research Article

Novel ion chromatography using a cationic coordination–unsaturated (hydrated) complex immobilized on a packing material as an anion-exchange group was investigated. This group, named as ‘charged complex anion-exchange group (CCAG)’, has not only normal anion-exchange ability, but also ligand-exchange ability because of its Lewis-acidic nature, and this novel chromatographic system can have specific anion-exchange selectivity different from normal anion chromatography. Several CCAGs, such as copper(II) and cadmium(II) complexes with bis(2-pyridylmethyl)amino group bonded on a hydrophilic vinyl polymer, showed unique anti-Hofmeister-type selectivity patterns for monovalent inorganic cations. During chromatographic comparison between many CCAGs formed from various divalent metal cations and several immobilized ligands having 2-pyridylmethyl and/or 2-quinolylmethyl pendant arm(s), it was found that the anion-exchange selectivity of CCAGs is controlled mainly by the hardness/softness of their central metal cations as Lewis acids, and their steric nature such as extent of shielding on their ligand-exchange cite and their steric bulkiness. Furthermore, the use of CCAGs formed from these metals and N,N-bis(2-pyridylmethyl)octadecylamine pre-coated on a reversed-phase HPLC column was discussed.