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  • 1
    ISSN: 1612-1112
    Keywords: Reversed-phase chromatography ; Homologous series ; Hydrocarbonaceous bonded phases ; Substituent effect ; Quantitative structure-retention relationships
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Linear free-energy relationships are manifest in the linear dependence of the logarithmic retention factor on the carbon number for homologous series in reversedphase chromatography and allow the comparison of the free-energy increments of substituents for retention of a given elute by different stationary phases. Three methods were used for such comparison. In the first two, methylene group selectivities obtained from retention data obtained with homologous series on different hydrocarbonanceous bonded phases were compared by using different approaches. In the third method the energetics of retention of the end groups such as phenyl-, bromo- and disulfide-moieties of homologous series were examined. The results show that at fixed mobile phase composition and temperature the free energy increments due to methylene groups upon retention by alkyl-silica stationary phases are identical. Only hydrocarbonaceous bonded phases with short (C1–C2) alkyl chains or functional groups of unusual shape show consistent differences from octyl- or octadecyl-silicas. The results broaden the theoretical basis for the development of quantitative structure-retention relationships to be used for the prediction or interpretation of retention data in reversed-phase chromatography.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1612-1112
    Keywords: Retention mechanism ; Reversed-phase chromatography ; Retention thermodynamics ; Mobile phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The physico-chemical framework is examined by comparing the predictions of three models for the combined effects of the composition of the hydroorganic mobile phase and the column temperature on the retention ofn-alkylbenzenes on hydrocarbonaceous bonded stationary phases. The “well-mixed” model leads to expressions for the dependence of retention on three factors which are equivalent to those derived previously from linear extrathermodynamic relationships. The “diachoric” model stems from the assumption that the mobile phase is microscopically heterogeneous and the “displacement” model is identical to the retention model most widely used in chromatography with polar sorbents and less polar solvents. Over limited ranges of mobile phase composition and temperature, each model does describe retention behavior. However, only the wellmixed model describes retention well over the entire range of mobile phase composition and temperature studied here. The success of the well-mixed model, and its limits, give insight into the role of the organic solvent in determining the magnitude of chromatographic retention on non-polar stationary phases with hydro-organic eluents.
    Type of Medium: Electronic Resource
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