Chelation ion chromatography of metal ions using high performance substrates dynamically modified with heterocyclic carboxylic acids Original Research Article

This study shows that stable high efficiency metal chelating substrates can be formed from neutral stationary phases by dynamically loading with low molecular weight complexing agents present in the mobile phase. Three complexing pyridine carboxylic acids, namely, picolinic, dipicolinic and quinaldic acids were used to dynamically coat both a C18silica gel and a polystyrene resin and the separation performance compared for groups of metal ions. Quinaldic acid gave the largest selectivity coefficients as it produced the most concentrated coating, while picolinic acid was too weakly adsorbed to give any significant metal retention apart from copper. Dipicolinic acid was found to be especially selective for uranium(VI). In general, retention order was the same on both stationary phases, but the polystyrene resin produced the most efficient separations. Interesting selectivity differences were found between the different acid coatings. For example, for dipositive ions, the retention order using a dipicolinic acid coating was Mn(II) < Cu(II) < Ni(II) < Zn(II) < Pb(II) < Cd(II), whereas using quinaldic acid it was Mn(II) < Pb(II) < Cd(II) < Zn(II) < Ni(II) < Cu(II).