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ARS Home » Research » Publications at this Location » Publication #64536

Title: NORMAL-PHASE HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY OF TOCOPHEROLS ON POLAR PHASES

Author
item ABIDI, SHARON
item Mounts, Timothy

Submitted to: Journal of Liquid Chromatography
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Tocopherols are naturally occurring antioxidants and exist in vegetable oils as minor constituents. Separations and characterization of various forms of tocopherols are required to assess the impact of genetic modification of oil seeds on their distribution. Accurate methods are needed to improve assay procedures. Analytical methods have been developed. Tocopherol components have been separated with different types of silica-based columns and analyzed with a fluorescence detector. The new methods can be used in the routine analysis of mixtures of tocopherols in plant oils and are particularly useful for trace analyses. The analytical data provides useful information on differences in tocopherol levels due to genetic engineering of oilseeds.

Technical Abstract: Five plant tocopherols were separated by normal-phase high-performance liquid chromatography (HPLC) on aminopropysilica or diol-bonded silica with fluorescence detection. HPLC characteristics of these compounds were studied under various mobile phase conditions. Mobile phases employed binary solvent systems comprising a hydrocarbon and an alcohol, an ether, or an ester. Separation factors (alpha) of adjacent ring-methylated tocol components were determined. Employment of aprotic weakly polar modifiers in the mobile phases increased the alpha values for the pair of 5,8- and 7,8-dimethyltocol, but decreased those for the 5,7- and 5,8-dimethyltocol pair. Both component resolution and detection sensitivity were adversely affected by the use of a diol-bonded silica phase of large particle size. HPLC with cyclohexane-binary eluents invariably led to lower values of analyte capacity factors (k prime) than with hexane counterparts. Further, regardless of the type of column evaluated, the tocol isomers eluted in an ethereal mobile phase in the order of increasing k prime values: k prime (tetrahydrofuran)