Determination of critical micelle concentrations of anionic surfactants based on ligand exchange micellar electrokinetic chromatography Original Research Article

A new method for determining the critical micelle concentration (CMC) of anionic surfactants by ligand exchange-micellar electrokinetic chromatography (LE-MEKC) has been developed. In the separation of amino acid enantiomers by LE-MEKC using a copper complex with l-hydroxyproline as a chiral selector, it has been noted that the addition of anionic surfactants to the electrolyte causes the reversal of the enantiomer migration order EMO. The point of reversal is correlated with the CMC. Resolution (Rs) decreases with the addition of surfactant below the CMC and increases above the CMC. The inflection point at which Rs equals zero was used for the calculation of the CMC. Based on this fact, the CMCs of anionic surfactants sodium n-decyl sulphate, sodium dodecyl sulfate and sodium n-tetradecyl sulphate in 25 mM CuSO4, 50 mM l-hydroxyproline at pH 4 have been determined. The CMCs in the presence of 2.5% acetonitrile were also determined. Results show that the CMCs of anionic surfactants increased with the addition of acetonitrile.