Micellar Electrokinetic Chromatography

Abstract

Abstract Micellar electrokinetic chromatography (MEKC) is a highly efficient miniaturized separation technique that is performed with the same experimental set‐up that is used with capillary electrophoresis (CE). While the separation principle of CE is based on differences in the electrophoretic mobility of the solutes to be separated (only charged species can be separated), in MEKC separation is also based on differences in the distribution constants between two phases migrating at different velocity due to electrokinetic effects. The second phase is introduced into the separation electrolyte by adding an ionic surfactant (anionic or cationic) at a concentration above the critical micelle concentration (CMC). Aggregates of surfactant monomers (micelles) are present in the separation electrolyte. These aggregates have an electrophoretic mobility and are able to incorporate solutes or interact strongly with species dissolved in the surrounding medium. MEKC extends the applicability of CE to neutral solutes. In addition, MEKC has been proven to be superior to CE in the separation of very complex mixtures of solutes with similar electrophoretic mobility, because of the various factors that are available for the manipulation of separation selectivity. Currently, MEKC can be regarded as a separation technique with a similar scope to that of reversed‐phase high‐performance liquid chromatography (RPHPLC), having advantages over the latter concerning the efficiency of the separation system, separation speed, cost and tolerance to matrix constituents, as in MEKC no stationary phase is present that can be fouled by irreversible sorption of matrix constituents of the sample. Owing to the small injection volume (a few nanoliters) and small detection volume that is necessary to avoid intolerable instrumental band broadening, current MEKC instrumentation restricts the applicability of MEKC to the determination of those compounds in complex mixtures that are present in concentrations sufficiently high with respect to the limits of detection that can be obtained with such instrumentation.