Anion selectivity, micellar chromatography

L. Zhu, C. Tu, and H. K. Lee, On-Line Concentration of Acidic Compounds by Anion-Selective Exhaustive Injection-Sweeping-Micellar Electrokinetic Chromatography, Anal. Chem. 2002, 74, 5820. 

Kim, J.-B., Otsuka, K., and Terabe, S., Anion selective exhaustive injection-sweep-micellar electrokinetic chromatography, J. Chromatogr. A, 932, 129, 2001. 

Many pharmaceutical preparations contain multiple components with a wide array of physico-chemical properties. Although CZE is a very effective means of separation for ionic species, an additional selectivity factor is required to discriminate neutral analytes in CE. Terabe first introduced the concept of micellar electrokinetic capillary chromatography (MEKC) in which ionic surfactants were included in the running buffer at a concentration above the critical micelle concentration (CMC) [17], Micelles, which have hydrophobic interiors and anionic exteriors, serve as a pseudostation-ary phase, which is pumped electrophoretically. Separations are based on the differential association of analytes with the micelle. Interactions between the analyte and micelles may be due to any one or a combination of the following electrostatic interactions, hydrogen bonding, and/or hydro-phobic interactions. The applicability of MEKC is limited in some cases to small molecules and peptides due to the physical size of macromolecules... 

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