Journal
CHROMATOGRAPHIA
Volume 81, Issue 3, Pages 373-385Publisher
SPRINGER HEIDELBERG
DOI: 10.1007/s10337-017-3454-4
Keywords
Reversed-phase liquid chromatography; Retention; Selectivity; Solvation parameter model; System maps; Octylsiloxane-bonded silica stationary phase; Diisobutyloctadecylsiloxane-bonded silica stationary phase; Superficially porous particles
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The system constants of the solvation parameter model are used to prepare system maps for the retention of small neutral compounds on an octylsiloxane-bonded (Kinetex C8) and diisobutyloctadecylsiloxane-bonded (Kinetex XB-C18) superficially porous silica stationary phases for aqueous mobile phases containing 10-70% (v/v) methanol or acetonitrile. Electrostatic interactions (cation-exchange) are important for the retention of weak bases with acetonitrile-water but not for methanol-water mobile phases. Compared with an octadecylsiloxane-bonded silica stationary phase (Kinetex C18) retention is reduced due to a less favorable phase ratio for both the octylsiloxane-bonded and diisobutyloctadecylsiloxane-bonded silica stationary phases while selectivity differences are small and solvent dependent. Selectivity differences for neutral compounds are larger for methanol-water but significantly suppressed for acetonitrile-water mobile phases. The selectivity differences arise from small changes in all system constants with solute size and hydrogen-bond basicity being the most important due to their dominant contribution to the retention mechanism. Exchanging the octadecylsiloxane-bonded silica column for either the octylsiloxane-bonded or diisobutyloctadecylsiloxane-bonded silica column affords little scope for extending the selectivity space and is restricted to fine tuning of separations, and in some cases, to obtain faster separations due to a more favorable phase ratio. For weak bases larger differences in relative retention are expected with acetonitrile-water mobile phases on account of the additional cation exchange interactions possible that are absent for the octadecylsiloxane-bonded silica stationary phase.
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