Aminophosphonate-functionalized silica: A versatile chromatographic stationary phase for high-performance chelation ion chromatography

The chromatographic behavior of alkaline earth metals, Cu(Il), Mn(II), Co(I I), Zn(II), Ni(II), Pb(II), and Cd(II) on a chelating aminomethylphosphonic acid-functionalized silica column was studied in eluants with high ionic s trength to suppress ion exchange. Unusual variations were found in plots of capacity factor against pH demonstrating changes in retention order, sugge sting a change in the coordination of metal ions from O, O to N, O, O chela tion. Increased affinity of the chelating ion exchanger to heavy metals and in particular Mn(II) was observed at low pH. Examples are shown of high-ef ficiency separations of groups of metal species with varying retention orde rs at different pH values, including a separation of eight metal species in under 16 min. These characteristics make aminophosphonate chelating substr ates a useful and more versatile phase for high-performance chelation ion c hromatography than iminodiacetate phases, (C) 1999 Academic Press.