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

Anionic dimeric surfactants with hydrophilic spacers containing two to six oxygen atoms were synthesized and applied as pseudostationary phases in micellar electrokinetic chromatography. Their selectivity was determined via linear solvation energy relationships. There were no differences in cohesiveness, polarizability or dipolarity with increasing spacer length, but there was a clear trend in increasing hydrogen bond accepting ability, and a concomitant decrease in hydrogen bond donating ability. The different selectivity of these dimeric surfactants compared to sodium dodecylsulfate can be useful for optimizing separations of mixtures of solutes for which these types of interactions are important. Their critical micelle concentrations were in the range of 0.2–0.3 mM, except for the surfactant with the shortest spacer (<0.03 mM), and are much lower than those of conventional surfactants used in micellar electrokinetic chromatography.