Separation selectivity in micellar electrokinetic chromatography using different anionic surfactants as pseudo-stationary phases

Micellar electrokinetic chromatography (MEKC) and ligand exchange-MEKC have been widely used for the separation of achiral and chiral compounds. For the separation of different compounds, one expects to obtain the desired different separation selectivity by choosing different surfactants as pseudo-stationary phases. This paper describes a comparative study on the separation selectivity in MEKC and LE-MEKC using different anionic surfactants such as sodium dodecyl sulfate (SDS), sodium alkyl polyoxyethylene sulfate (AES-Na) and sodium alpha -sulfonated fatty acid methyl esters (alpha -SF-Na). Different selectivities were observed with these anionic surfactants. For the separation of aromatic derivatives by MEKC, better selectivity was obtained by using AES-Na than SIDS micellar phases. For the simultaneous separation of positional enantiomers of o-, m- and p-fluoro-DL-phenylalanine by LE-MEKC, the SDS micellar phase provided the best selectivity among these anionic surfactants. Furthermore, the critical micelle concentrations (CMC) of these surfactants were also estimated by LE-MEKC.