Monitoring the interactions of tocopherol homologues with reversed-phase stationary HPLC phases by 1H suspended-state saturation transfer difference high-resolution/magic angle spinning NMR spectroscopy.

The separation process in reversed-phase high-performance liquid chromatography employing C18 phases is mainly due to hydrophobic interactions. The separation of tocopherol isomers, exhibited by the C30 phases, however, is additionally driven by shape selectivity. This phenomenon is investigated by suspended-state nuclear magnetic resonance spectroscopy using the saturation transfer difference technique, which was originally introduced to study protein-ligand interactions. The interaction strength between beta-/gamma-tocopherol and three different stationary phases was estimated qualitatively. The nuclear magnetic resonance data are compared to chromatographic data, and a similar mode of interaction between the analytes and the stationary phases is elucidated.