Reversed-phase high-performance liquid chromatographic separations of tocopherols

The retention behavior and separation characteristics of five natural products alpha-, beta-, gamma-, delta-, and zeta(2)-tocopherols and their acetyl derivatives were studied by reversed-phase high-performance liquid chromatography (HPLC)-fluorescence detection. Investigated stationary phases included an octadecyl polyvinyl alcohol (ODPVA) column, several octadecylsilica (ODS) columns, and a pentafluorophenylsilica column. Mobile phases comprised methanol (or acetonitrile) and water at variable proportions. Separation factors for beta- and gamma-tocopherol isomers and capacity factors of the five tocopherols were determined under various conditions. The beta- and gamma-tocopherols were separable on ODPVA but not on ODS. However, the beta-gamma pair was resolved with the latter column only as their ester derivatives. HPLC with mobile phases containing alkanols with carbon atoms greater than 2 favored the separation of the beta-gamma pair on ODS and yielded results diametrically different but complementary with those obtained with the ODPVA phase. The combined effects of mobile phases, stationary phases and antioxidant structures on component separations were delineated. (C) 1997 Elsevier Science B.V.