Capillary electrophoretic separation of metal ions using complex forming equilibria of different stabilities

摘要

Capillary electrophoresis was investigated for the determination of metal cations in the presence of various complexing agents. Separation of most metal ions is complicated by their similar electrophoretic mobilities and their weak UV absorption. In this study, the use of ligands forming metal complexes of different stabilities was examined. These complexing agents can selectively modulate the mobility of cations by forming metal complexes with varying degrees of stability. To cover a wide range of complex stability, different agents were studied such as α-hydroxyisobutyric acid (lg β 2...5), 8-hydroxyquinoline-5-sulfonic acid (lg β 7...12) and ethylenediaminetetraacetic acid (lg β 14...20). In the experiments, a model mixture of five metal ions(Cu, Zn, Pb, Ni and Fe) was used for all ligands, although in practice complexing agents and separation parameters will be chosen according to the properties of the analyzed cations. Using computer simulation, the average complexation degree for each metal ion with the different ligands under the chosen separation conditions was calculated. Detection was carried out by direct or indirect UV absorption due to the properties of the complexing agent or the formed complexes.