20 research outputs found
Retention indices in micellar electrokinetic chromatography
No full textThe use of retention indices in micellar electrokinetic chromatography (MEKC) is evaluated both from a theoretical and a practical point of view. Fundamental equations for the determination of retention indices in MEKC are described, showing that retention indices are independent of the surfactant concentration. Possibilities as well as limitations of different homologous series as reference standards are described. In addition, the practical application of retention indices for identification, investigation of solute-micelle interactions, characterization and classification of pseudo-stationary phases and determination of solute lipophilicity are discussed
Solute retention and resolution in parallel-current open tubular liquid chromatography
No full textA polemic is given to show that the solute retention equation for micellar electrokinetic capillary chromatog. can be used to derive the capacity factor in parallel-current open tubular liq. chromatog. as developed by K. Slais et al. (J. Chromatog. 1992, 605, 167; J. Microcol. Sep. 1993, 5, 63). Differences in flow ratio caused by inhomogeneity of the retentive film will not affect the calcd. capacity factor in contrast to the dependence on flow ratio of the reduced capacity factor derived by Slais et a
Optimization of the elution range in micellar electrokinetic capillary chromatography
No full textThe resolution of neutra! solutes in micellar electrokinetic capillary chromatagrophy is influenced by the migration time of the electroosmotie flow, tEoF' the migration time of the micelles, tMe, and the capacity factors of the solutes, k. The resolution of a separation can be improved by increasing the elution window and by optimizing the capacity factors of the solutes. The influence of the buffer pH, surfactant concentration and organic modifier content of the electrolyte system on both the elution window and the capacity factors was investigated
Characterization of pseudostationary phases in micellar electrokinetic chromatography by applying linear solvation energy relationships and retention indexes
No full textParameters controlling the elution window and retention factors in micellar electrokinetic capillary chromatography
No full textThe resolution of uncharged compounds in micellar electrokinetic capillary chromatography (MECC) is influenced by both the elution window and the retention factors of the compounds. The influence of the electroosmotic mobility and the effective mobility of the micelles on the elution window is treated theoretically and the effect of different experimental conditions on the elution window and the retention factors is determined. Although these variables cannot be controlled independently in many cases, the resolution in MECC can be improved by adjusting the composition of the applied electrolyte system. This is demonstrated for several electrolyte systems with different pH values, ionic strengths, surfactant concentrations and organic modifier contents. Further, the influence of the applied field strength, capillary surface modifications and the alkyl chain length of the surfactant are evaluat
Migration behaviour of monovalent weak acids in micellar electrokinetic chromatography; mobility model versus retention model
No full textMigration of charged compounds in micellar electrokinetic chromatography (MEKC) is based on micellar solubilization as well as electrophoretic migration. Consequently, the migration behaviour of these compounds can be described with a retention model or a mobility model. Both models are discussed and evaluated for the migration behaviour of monovalent weak acids in a sodium dodecyl sulphate micellar system. We have shown that the calculation of retention factors may be troublesome for hydrophobic compounds, due to interaction with surfactant molecules in the aqueous phase. Therefore, the mobility model is preferable. The simultaneous determination of dissociation constants by spectroscopic and electrophoretic methods is discussed and apparent dissociation constants in micellar media are determined, showing that pKa shifts may occur in MEKC analyses, due to micellar solubilization. Furthermore, a sample stacking procedure is described, based on differences in overall effective mobilities between aqueous and micellar electrolyte systems
Migration behaviour of micelle counterions in micellar electrokinetic chromatography: Influence on micelle mobility, efficiency and selectivity
No full textEvaluation and characterization of pseudo-stationary phases in Micellar Electrokinetic Chromatography
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