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 t he separation of different compounds, one expects to obtain the desired dif ferent separation selectivity by choosing different surfactants as pseudo-s tationary phases. This paper describes a comparative study on the separatio n 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). D ifferent selectivities were observed with these anionic surfactants. For th e separation of aromatic derivatives by MEKC, better selectivity was obtain ed by using AES-Na than SIDS micellar phases. For the simultaneous separati on of positional enantiomers of o-, m- and p-fluoro-DL-phenylalanine by LE- MEKC, the SDS micellar phase provided the best selectivity among these anio nic surfactants. Furthermore, the critical micelle concentrations (CMC) of these surfactants were also estimated by LE-MEKC.