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

A new method for determining the critical micelle concentration (CMC) of an ionic 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 selecto r, it has been noted that the addition of anionic surfactants to the electr olyte 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 infle ction 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 sulpha te, 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 prese nce of 2.5% acetonitrile were also determined. Results show that the CMCs o f anionic surfactants increased with the addition of acetonitrile. (C) 2000 Elsevier Science B.V. All rights reserved.