Reversed-phase retention characteristics of tocotrienol antioxidants

Mixtures of alpha-, beta-, gamma- and delta-tocotrienols were separated by reversed-phase (RP) high-performance liquid chromatography (HPLC). Four set s of subcomponents (cis/cis-, cis/trans-, trans/cis- and trans/trans-geomet rical isomers) were further resolved under various HPLC conditions. Retenti on characteristics of the beta- and gamma-isomers on octadecylsilica (ODS) were indistinguishable. However, complete separations of all sixteen tocotr ienol components were achieved by RP-HPLC with a nonsilica-based octadecano yl polyvinyl alcohol (ODPVA) column. In this system, beta-tocotrienol peaks were found to interpose alternatively with those of gamma-tocotrienols, wh ich was attributable to apparent differences in intrinsic molecular polarit y and hydrophobicity. HPLC with a pentafluorophenylsilica (PFPS) column led to partial separations of tocotrienols, of which two subclass species rema ined unresolved. Peak profiles obtained with PFPS columns of different pack ings were similar but not identical. Nonetheless, the component elution pat terns on PFPS were markedly different from those on ODPVA. Furthermore, the use of a triacontylsilica column enabled separations of fifteen components and yielded an elution order parallel to that of an ODPVA column. In gener al, the elution sequence of tocotrienols appeared to depend largely on the type of organic modifier used, despite the subtle influence of stationary p hases and the isomeric characteristics of alkenyl chains. While poorly reso lved on silica, geometrical isomers were readily separated on the RP phases studied with acetonitrile-water as the preferred eluent. Factors affecting analyte retention and component resolution were delineated. (C) 1999 Publi shed by Elsevier Science B.V. All rights reserved.