Counter-current chromatography using hexane/surfactant-containing water solvent systems.

We developed a n-hexane/surfactant-containing water solvent system in counter-current chromatography (CCC) in order to separate hydrophobic compounds. By using the upper phase as the mobile phase, we have separated steroid samples. Retention times of steroids progesterone and delta4-androstene-3,17-dione increased slightly by increasing the concentration below the critical micellar concentration (CMC) of surfactant sodium 1-heptanesulfonate. However, the retention times increased drastically while the SHS concentrations were above the CMC. The partition of these two steroids in the two phases was significantly dependent on the interaction with micelles. Aromatic hydrocarbons were not retained by the lower phase no matter what the surfactant concentrations were. Their hydrophobic interaction with n-hexane greatly exceeded that with the micellar solution. The retention times of esters, however, were only slightly affected by the surfactant addition even above the CMC. The weaker interaction between esters and the micellar solution was probably due to their higher polarity. The micellar solvent systems provide an alternative way for hydrophobic sample separations in CCC, but the performance is limited.