Linear solvation energy relationships of anionic dimeric surfactants in micellar electrokinetic chromatography

The range of selectivities of pseudostationary phases (PSPs) available for micellar electrokinetic chromatography is limited, and there continues to be interest in the synthesis and evaluation of novel PSPs. With the unique selectivity of lithium perfluorooctanesulfonate (LPFOS) in mind, we synthesized anionic dimeric surfactants with fluorinated spacers of various lengths. Their selectivities, analyzed via linear solvation energy relationships, are similar to those of their non-fluorinated analogues, although the results indicated that they are somewhat less polarizable. While it can be concluded that fluorination has some influence on the behaviour of these dimeric PSPs, the influence on the selectivity is not as dramatic as in LPFOS. This can be explained by the inferred poor hydration of the fluorinated spacer and the positioning of the fluorine substituents, too distant from the surfactant head groups to fully exert the strong inductive effect required to significantly influence the head group chemistry.