Recent studies have shown that due to the presence of α-tocopherol transfer protein (α-TTP) in liver, there is a mechanism that preferentially takes up and uses RRR-α-tocopherol (post-hepatic pathway). However, several reports suggest that the liver is not the only determinant tissue in the utilization of vitamin E. Progress in analytical methods has recently stimulated studies on the chirality of vitamin E. It has been shown that there is no biodiscrimination in the transfer of orally administered vitamin E stereoisomers until the chylomicron stage. The fate of vitamin E stereoisomers within the smaller fragments resnlting from hydrolysis in the blood of the chylomicrons by lipoprotein lipases, is unknown (pre-hepatic pathway). Concerning the pre-hepatic pathway, and in particular how vitamin E incorporated in lipoproteins is taken up by a peripheral tissue where no α-TTP is expressed, an in vitro experimental model was investigated. Results suggested that skeletal muscle myoblasts do not discriminate vitamin E stereoisomers.

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A quantitative analysis method of niacin in food by HPLC was reported in our previous study. That method required more than three-hour washing of the column after each sample injection because a sample solution contained many impurities besides niacin. So a column-switching HPLC method was evaluated to improve the reported method in quantifying niacin in food. The amount of niacin, in this study, was determined as nicotinic acid equivalence after 2hr-hydrosis of nicotinamide in 0.5 M sulfuric acid. The separation was achieved on a SP-2SW (4.6×250 mm) column and NH2-N (4.6×100 mm) precolumn using a 5 mM KH_2PO_4 (pH 3.0 or 2.8) : CH_3CN=95:5 (v/v) as the mobile phase with detection at 260 nm. The sample injection volume of HPLC was 20 μl. Under the HPLC conditions at the pH 3.0 mobile phase, the linear calibration curve exhibited 1.000 of correlation coefficient from 0.1 to 10 μg/ml of nicotinic acid levels. The detection limit of nicotinic acid was 0.05 μg/ml, and the quantification limit of that sample was 0.1 mg/100 g. For some samples that could not be analyzed at the pH 3.0 mobile phase, satisfactoly analytical results were obtained at the pH 2.8, Consequently, the pH 2.8 mobile phase was adopted as the best mobile phase for quantitative analysis of niacin in food. The detection limit at the pH 2.8 mobile phase was proved to be as low as 0.2 mg per 100 g of sample.

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