Characterization and comparison of the chromatographic performance of conventional, polar-embedded, and polar-endcapped reversed-phase liquid chromatography stationary phases

We have evaluated and compared the performance of several conventional C18 phases with those possessing either a polar-endcapping group or a polar-embedded group within the primary alkyl ligand and found distinct differences in the chromatographic behavior among the three groups, as well as a high degree of variability within each group. The trend is for the polar-endcapped phases to display similar hydrophobic retention characteristics as the conventional C18 columns, but to express higher hydrogen bonding capacities and silanol activity. The polar-embedded phases displayed the opposite behavior, with a greatly reduced hydrophobic nature compared to the conventional and polar-endcapped C18 phases, and also a very much reduced silanol activity. Most interestingly, it appears that ionic or dipole interactions play a significant role in the overall retention behavior of the polar-embedded phases towards basic and acidic analytes.