Quantitative investigation on the stacking of metal ions induced by another metal ion based on moving substitution boundary electrophoresis†
Abstract
In this paper, a novel model for the stacking of metal ions via another metal ion was developed based on a dynamic equilibrium system (DES) composed of moving substitution boundary (MSB) and moving chelation boundary (MCB). With Cu2+, Co2+ and EDTA as an example, a substitution reaction took place between Cu2+ and [Co-EDTA]2−, and resulted in the formation of MSB, and Co2+ released from [Co-EDTA]2− reacted with EDTA, which resulted in the formation of MCB and [Co-EDTA]2−, the produced [Co-EDTA]2− reacted again with Cu2+. The reaction between Cu2+, [Co-EDTA]2−, and Co2+, EDTA were repeated. The concentration of Co2+ and [Co-EDTA]2− was stacked accompanying the formation of MSB and MCB until the above two reactions reached equilibrium. Relevant experiments were performed and the results indicated that: (1) Cu2+ can be used for the stacking of Co2+ and higher than 70-fold preconcentration of Co2+ was achieved in capillary electrophoresis (CE); (2) the concentration of Cu2+ had a key role in the stacking of Co2+, a higher Cu2+ concentration resulted in a better focusing efficiency; (3) the initial concentration and zone length (Linitial) of [Co-EDTA]2− were the major factors on enrichment. Furthermore, experiments based on MSB were performed with multi-metal ions (such as Cu2+, Co2+, Ni2+ and Pb2+), which demonstrated the potential application of the MSB-based technique for the separation and stacking of multi-metal ions.