Characterization and application of pseudostationary phases in micellar electrokinetic chromatography (MEKC)

Various micellar, mixed micellar and polymeric pseudostationary phases were evaluated using linear solvation energy relationships (LSER) and applied for the separation of various groups of pharmaceutically and environmentally relevant compounds in micellar electrokinetic chromatography (MEKC) and mixed micellar electrokinetic chromatography (MMEKC).; First, individual as well as mixtures of bile salt surfactants and/or sodium dodecyl sulfate (SDS) were employed to separate a group of seventeen structurally similar corticosteroids. Addition of SDS to the mixtures of bile salt micelles resulted in significant extension of the elution window and subsequently improvement in resolution. The separation of a complex mixture of seventeen corticosteroids was further improved by employing various bile salt and/or alkylsulphonate mixtures for use in MMEKC. Retention behavior of corticosteroids in SDS and bile salt micelles was examined using linear solvation energy relationships (LSER). The effects of alkylsulphonate carbon chain length and concentration on capacity factor, selectivity, efficiency, and the size of the elution window were investigated. LSER models were also used to investigate additional MEKC surfactant systems including mixed bile salt systems (e.g. sodium deoxycholate (SDC) and sodium cholate (SC)) and mixed SDS/bile salt systems (e.g. SDS/SC and SDS/SDC). It was found that the migration behavior of a group of 60 uncharged aromatic compounds is influenced primarily by their size and hydrogen bond acceptor strength in all systems investigated. Mixed bile salt systems also provided results differing from the two individual systems. In addition, LSER analysis was applied for the study of a mixed fluorocarbon (lithium perfluorooctane sulphonate (LiPFOS))/hydrocarbon (lithium dodecyl sulfate (LiDS)) surfactant system. Elution patterns of various solutes in mixed micellar systems were compared and rationalized through results of LSER analysis.; Second, an ionic tri-block co-polymer, poly(methyl methacrylate/ethyl acrylate/methacrylic acid) (Elvacite 2669) was used as a pseudostationary phase in MEKC. Highly hydrophobic compounds such as polycyclic aromatic hydrocarbons (PAH's) and fullerenes were separated using Elvacite 2669 as an MEKC pseudostationary phase along with high percentages of organic modifier. The effect of addition of methanol to Elvacite 2669 MEKC systems was studied using LSER models. It was found that retention in these polymeric/methanolic pseudostationary phases is primarily influenced by the size of the molecule and their hydrogen bond accepting basicity. LSER results obtained in Elvacite 2669/methanolic MEKC systems were compared to results obtained in C-18 reversed phase liquid chromatography (RPLC) systems using methanol/water mobile phases.