Separations of tocopherols and methylated tocols on cyclodextrin-bonded silica

-, β-, γ-, and δ-tocopherols (methyl-substituted tocols) and 5,7-dimethyltocol were separated by normal-phase HPLC on β- or γ-cyclodextrin-bonded silica (CDS) with fluorescence detection. The HPLC behavior of the tocol components was studied under various mobile phase conditions. Hexane or cyclohexane was used in combination with oxygen-containing solvents (alcohol, ether, and esters) in binary and ternary mobile phases. Capacity factors (k′) and separation factors () for adjacent tocol components were determined. Incorporation of non-polar ethers in the hydrocarbon (hexane or cyclohexane) mobile phases favored the separation of β- and γ-tocopherols with improved values, which enabled trace analysis of the β-isomer present in soybean oil. Analyte solutes tended to be more strongly adsorbed in mobile phases containing branched-chain alcohols and ethers than in those containing the corresponding straight-chain solvents. Generally, the k′ values obtained with hexane mobile phases or with the β-CDS phase were greater than those observed in HPLC with cyclohexane mobile phases or with the γ-CDS phase.