3.1 Analysis of mixed tocopherols
As shown in Fig 2a, the components of mixed tocopherols are four kinds of tocopherol monomers and some impurities with a less polarity than α-tocopherol. And we all know that the mixed tocopherols are mainly obtained by molecular distillation under reduced pressure and high temperature after esterification of fatty acids, triglyceride and crystallization of sterols (Ito et al. 2007). After comparison with the standard substances, we speculated that the impurities may be fatty acid methyl ester. The four tocopherols and impurities are thereby separated in the following order: δ-T, (β + γ)-, α-tocopherol and impurities with increasing Rf values: 0.69, 0.79, 0.90, 0.95, this order showed that the polarity of our target γ- tocopherol is between δ- and α-tocopherol. In order to obtain the high-purity target γ-tocopherol, we have to remove not only impurities, but also α- and δ-tocopherol, so it is difficult to separate target substance for the reasons given above. The total tocopherol content in mixed tocopherol was 91.62%, with the contents of α-, β-, γ- and δ- tocopherol were 7.17%, 1.47%, 60.04% and 24.41%, respectively. And the impurities were around 6.91%.