Retention mechanisms micellar liquid chromatography

Garcia Pinto, C. P6rez Pavon, J.L. Moreno Cordero, B. Micellar liquid chromatography of zwitter-ions Retention mechanism of cephalosporins. Analyst, 1995,120, 53-62... 

The first applications of Micellar Liquid Chromatography (MLC) in analytical chemistry were published in 1984. TTie reports showed the interest of using micellar mobile phases in the analysis of plasma [1], proteins [2] and pesticides [3]. However, the res rch on MLC has been largely dedicated to the retention mechanism inside the chromatographic system and the relationships between the retention behavior and hydrophobicity of solutes. Indeed, micellar mobile phases are quite interesting from a mechanistic standpoint, but some practical analytical utility had to be demonstrated before they could be considered as an alternative to the more traditional aqueous-organic mobile phases. 

Micelles and cyclodextrins are the most common reagents used for this technique. Micellar electrokinetic capillary chromatography (MECC or MEKC) is generally used for the separation of small molecules [6], Sodium dodecyl sulfate at concentrations from 20 to 150 mM in conjunction with 20 mM borate buffer (pH 9.3) or phosphate buffer (pH 7.0) represent the most common operating conditions. The mechanism of separation is related to reversed-phase liquid chromatography, at least for neutral solutes. Organic solvents such as 5-20% methanol or acetonitrile are useful to modify selectivity when there is too much retention in the system. Alternative surfactants such as bile salts (sodium cholate), cationic surfactants (cetyltrimethy-lammonium bromide), nonionic surfactants (poly-oxyethylene-23-lauryl ether), and alkyl glucosides can be used as well. 

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