Methods for concentrating metal ions prior to analysis by ion chromatography or capillary electrophoresis

In ion chromatography and particularly in capillary electrophoresis, it is often necessary to preconcentrate metal ions to be determined and to remove larger amounts of matrix ions such as Na+, Mg2+, and Ca2+. Several general techniques for concentration of selected metal ions are reviewed and illustrated by specific examples. These techniques include the use of chelating resins and the formation of soluble complexes in solution with subsequent retention by ordinary solid-phase extraction (SPE) columns. Many of the chelating resins used in the past for preconcentration of metal cations have been relatively inefficient. More effective resins can be created by careful attention to the particle size and physical structure of the resin, its chelating capacity, and the selectivity and kinetics of the chelating groups present in the resin. Likewise, carefully designed soluble complexing reagents can be used effectively in conjunction with modem SPE techniques. These principles are illustrated by new types of chelating resins and reagents that we have prepared and tested.