Selected normal-phase HPLC and GLC methods for the analysis of tocopherols in vegetable oils were evaluated critically. Repeatability, accuracy and/or recovery were determined for both methods and compared to data mentioned in the official methodology. The best accuracy and repeatability was obtained for the normal-phase HPLC technique based on the AOCS official method Ce 8-89, which can probably be explained by the short and easy sample preparation. Tocopherol levels of sixteen fully refined vegetable oils were determined by both, GLC and HPLC. Regression analysis showed that tocopherol levels obtained by GLC were about 6.1% higher than the corresponding HPLC data. Although the reported recovery of the GLC method was good, it seems that an additional TLC separation has to be introduced in the sample preparation to avoid peak overlap between tocopherols and some interfering substances present in the unsaponifiable fraction.
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Greyt et al. (1998) studied this question.