Chelation ion chromatography of trace metal ions using metallochromic ligands

Hydrophobic metallochromic ligands can be used to coat high-performance reversed-phase substrates producing chelating stationary phases with the capacity to separate metal ions. To date the main approaches have been to ‘pre-coat' the substrate with the ligand and use it with a mobile phase containing an inorganic salt or alternatively to include the ligand itself within the mobile phase, where the ligand forms a ‘dynamic coating' on the stationary phase, which exhibits retention characteristics similar to the above pre-coated columns. The latter approach offers certain advantages, including increased column capacity, improved separation efficiency, differing selectivity, and the ability to exploit the ligand present in the mobile phase for the visible detection of the eluting metal ions. Here, the two techniques are compared, with the above differences illustrated and explained in terms of retention mechanisms and mobile/stationary phase effects.