Separation of water-soluble vitamins by micellar electrokinetic chromatography

The retention behaviour of eleven water-soluble vitamins in micellar electrokinetic chromatography (micellar EKC) was investigated in comparison with capillary zone electrophoresis. Sodium dodecyl sulphate (SDS) and sodium lauroylmethyl taurate were used as the anionic surfactants at concentrations of 0.05-0.2 M in micellar EKC. The retention times of cationic substances increased more rapidly with increasing concentration of the anionic surfactant than those of other substances. This result suggests that ion-pair formation between cationic substances and anionic surfactants contributes to the retention of the former. The difference in the structures of the two surfactants affects the retention behaviour of solutes, especially cationic substances. To clarify the effect of the micelle, an ion-pairing agent that does not form the micelle structure was employed. All solutes were successfully separated within 15 min by using a 650 mm x 0.05 mm I.D. fused-silica tube with a 0.05 M SDS solution (pH 9.0) to give theoretical plates ranging from 100,000 to 350,000.