A LIQUID-CHROMATOGRAPHIC METHOD FOR THE SIMULTANEOUS DETERMINATION OF ALPHA-TOCOPHEROL AND TOCOPHEROLQUINONE IN HUMAN RED-BLOOD-CELLS AND OTHER BIOLOGICAL SAMPLES WHERE TOCOPHEROL IS EASILY OXIDIZED DURING SAMPLE TREATMENT

A liquid chromatographic method for the simultaneous determination of α-tocopherol and tocopherolquinone in human red blood cells is described. Tocopherols in the red cell membrane are very susceptible to oxidation during sample processing. Red cell samples are saponified in the presence of a mixture of butylated hydroxytoluene, ascorbic acid, and pyrogallol and then extracted with hexane. The tocopherol compounds are separated on a C-18 column using a mobile phase containing 12% acetonitrile, 83% methanol, and 5% buffer (NaH2PO4 · H2O, 7.5 mM final concentration) and are detected electrochemically. The mixture of antioxidants is essential to avoid loss of the tocopherol compounds during processing of samples. The use of acetonitrile in the mobile phase results in the separation of tocopherolquinone from δ-tocopherol. The proposed method may be generally suitable for the analysis of biological samples where tocopherols are especially vulnerable to oxidation. The levels of tocopherolquinone and δ-tocopherol in normal red cells are quite small (less than 1% of α-tocopherol). The ratio of tocopherol and tocopherolquinone concentrations might serve as a useful index of the redox status of red cell membranes, particularly under in vitro conditions. © 1993 Academic Press, Inc.