Linear solvation energy relationships of anionic dimeric surfactants in micellar electrokinetic chromatography: I. Effect of the length of a hydrophobic spacer

The influence of the length of a flexible hydrophobic spacer on the selectivity of anionic dimeric surfactants was investigated. Disodium 1,ω-bis(decyloxymethyl)-dioxa alkane-1,ω disulfates with a spacer containing an ethylene, butylene, hexylene, octylene, decylene or dodecylene group were synthesized, and four of these were evaluated for use in micellar electrokinetic chromatography (MEKC) via linear solvation energy relationships (LSERs). There were no significant differences in the system constants of these surfactants, indicating that their micelles all have a very similar interface with the aqueous phase, regardless of the length of the hydrophobic spacer. Compared to sodium dodecylsulfate (SDS), these dimeric surfactants are slightly more cohesive, interact better with polarizable compounds, and are somewhat better hydrogen bond acceptors and worse hydrogen bond donors, while there is no difference in dipolarity. The critical micelle concentrations (CMCs) of these surfactants were in the order of 1 mM, except for the dimeric surfactant with a spacer containing an ethylene group, which had a CMC <0.03 mM.