Several new octadecylsilyl and polar-modified phases were synthesized. Chromatographic evaluations of these columns were performed using the Dolan and Engelhardt test mixtures. The applicability of these new phases was also evaluated with a mixture of acids, bases or neutral compounds. The distinct differences in the chromatographic behavior between the two groups as well as a high degree of variability within each group were observed. The polar-endcapped phases exhibit similar hydrophobic selectivity, higher hydrogen bonding capacities and silanol activity with reference to C18 columns. The polar-embedded phases display a greatly reduced hydrophobic nature and a significantly reduced silanol activity compared to the C18 phases.