A LINEAR SOLVATION ENERGY RELATIONSHIP STUDY OF THE EFFECTS OF SURFACTANT CHAIN-LENGTH ON THE CHEMICAL INTERACTIONS GOVERNING RETENTION ANDSELECTIVITY IN MICELLAR ELECTROKINETIC CAPILLARY CHROMATOGRAPHY USINGSODIUM ALKYL SULFATE ELUTION BUFFERS

We have used linear solvation energy relationships (LSERs) to study th e fundamental chemical interactions responsible for solute retention i n micellar electrokinetic capillary chromatography (MEKC). We investig ated retention in micellar solutions of sodium dodecyl sulfate (SDS), sodium decyl sulfate (SDecS), and sodium octyl sulfate (SOS). The purp ose of the study was to elucidate the effect of surfactant chain lengt h on the solute/micelle interactions that ultimately govern retention and selectivity in MEKC. The nature of the solute/micelle interactions were found to be nearly equivalent in all three systems, implying tha t the chromatographic selectivity in all three systems will be quite s imilar. Additionally, the LSERs show that solute size and hydrogen bon d basicity play the largest roles in determining solute retention and chromatographic selectivity. Finally, from the LSERs and an analysis o f the free energy of transfer of methylene units from water to the mic ellar phase (Delta G(CH2)degrees), we conclude that the solutes reside in the polar, hydrated head group region of the micelles, and not in the nonpolar core. Based on the Delta G(CH2)degrees values for five di fferent homologous solute series, the effect of the solutes' functiona l groups on the location and orientation of the solutes inside the mic elles is briefly discussed.