Characterization of pseudostationary phases in micellar electrokinetic chromatography by applying linear solvation energy relationships and retention indexes

The influence of different solute-micelle interactions on micellar solubilization is studied by using linear solvation energy relationship (LSER) modeling. The LSER results for six anionic micellar systems demonstrate that the migration behavior of neutral species in micellar electrokinetic chromatography (MEKC) is mainly determined by their molar volume and their hydrogen bond acceptor ability. Their polarity and hydrogen bond donor ability are shown to be of minor importance with these anionic surfactants. Large differences in selectivity were observed for sodium dodecyl sulfate (SDS) and mixed SDS/Brij 35 micellar systems, primarily due to different hydrogen bonding characteristics. It is demonstrated that retention indexes can be applied for quantitative characterization of pseudostationary phases in MEKC in a way similar to the use of the Rohrschneider-McReynolds scale in GC. This method facilitates classification of pseudostationary phases according to several solvatochromic quantities with a limited number of experiments, Using this approach, six anionic and two cationic micellar systems were classified according to their hydrogen bond donor and hydrogen bond acceptor strengths, respectively, giving results comparable to those obtained with the LSER models, The relationship between retention indexes and n-octanol-water partition coefficients is treated theoretically and is applied for the prediction of retention indexes in a mixed SDS/Brij 35 micellar system.