Focusing of anionic micelles using sample-induced transient isotachophoresis: computer simulation and experimental verification in MEKC.

The specific phenomenon of high-salt micelle focusing used as a preconcentration method for uncharged solutes in MEKC has been interpreted in terms of complementary transient isotachophoresis (tITP) process. High matrix chloride can focus anionic SDS micelles not only due to a field-enhanced effect but also by creating the tITP state in which chloride acts as a leading ion. The latter micelle-enrichment event was simulated by SIMUL software in order to understand tITP conditions under which micelle stacking can be expected to occur. Specifically, effects of chloride matrix concentration and the nature of BGE co-ion, performing a role of terminating ion, were explored. A greater extent of micelle stacking was observed at a higher chloride concentration in borate than in phosphate buffer system. This proof-of-principle simulation result was confirmed in real experiments using metal-based chemotherapeutic drugs. It was concluded that analyte enrichment requires prolonged interaction with the micelle, which is feasible at a proper ratio between sample matrix and BGE co-ion concentrations.