Reverse micelle chromatography for evaluation of partition of organic solutes to micellar pseudophases

The evaluation of solute partition from an organic solvent to a reverse micelle (RM) is critical for designing effective reaction systems and for synthesizing functional materials using the nano water-phase in the RM. Although spectroscopic methods have been extensively employed for determining the partition constants of solutes in the RM systems, their applications are limited to the case, in which the background absorption is low and the spectroscopic features of the solute are effectively varied by its partitioning to RMs. This paper proposes a novel chromatographic method to overcome this limitation of conventional methods. In the present system, a size-exclusion chromatographic column is used with RM solutions as mobile phases. The RM is excluded from the stationary phase and, therefore, is eluted first. A solute is eluted with the retention volume determined by its affinities to the stationary phase and the RM. The elution volumes of a solute measured by varying the concentrations of RM in the mobile phase allow us to determine its partition constant to the RM. The partition of phenols in hexadecyltrimethylammonium chloride and bromide RMs in chloroform is successfully evaluated without interferences from the UV-absorption of the media. The larger partition constant is confirmed for a smaller water/surfactant molar ratio (w) and for chloride than bromide as the RM counterion. This suggests that the nature of water is more strongly influenced by confinement in the RM cores for smaller w and the chloride counterion because water molecules are strongly imbibed by the interface.