• Aqueous normal phase;
  • Hydrophobic bases;
  • Polar bases;
  • Retention plots;
  • Silica hydride

In this study, the retention behavior of selected hydrophobic and polar bases on a minimally modified silica hydride phase was investigated. From these results and the associated retention plots, significant differences in the chromatographic dependencies of these two classes of basic compounds were evident. The polar bases exhibited strong retention with mobile phases of high organic solvent content, but displayed weak retention with mobile phases of high water content. In contrast, the hydrophobic bases showed “U-shape” retention dependencies, indicative of the interplay of both RP and normal-phase retention characteristics. These studies have demonstrated that hydrophobic and polar bases can be simultaneously separated on the same column either under typical RP-like or aqueous normal-phase-like conditions, respectively, with distinctive selectivity. Finally, the effects of temperature on the RP and aqueous normal phase modality of separations with these analytes were investigated, where discrete changes in retention behavior were also observed.