Method for the Determination of Vitamin E (total Tocopherols) in Serum.

A.CONSIDERABLE LITERATURE has developed with respect to the determination of vitamin E as total tocopherols. Several texts (1-3) present both chemical and biologic assay methods. Although the direct spectrophotometric determination of vitamin E in serum at its absorption peak of about 295 m is attractive, it is not practical because of very low sensitivity and the presence of many interfering substances. Only two of the oxidimetric color reactions for vitamin E appear sensitive enough for analysis of serum. One is oxidation (e.g., with silver nitrate) to give tocopheryiquinone with an absorption peak at about 265 m; it requires rigid control of conditions for precise results. The other is the Emmerie and Engel (4) color reaction with ferric chloride and , ‘-dipyridyl (bipyridyl) to give a red color, a reaction that is precise and easy to perform, and therefore the approach of choice for a routine clinical laboratory. Natelson (5) improved the sensitivity of this technic by substituting terpyridyl (2,2’,2”-tripyridine) for bipyridyl in this color reaction. Recently Caraway (6) reported a method for the estimation of serum iron and iron-binding capacity employing the very sensitive reagent, 2,4,6-tripyridyl-s-triazine (TPTZ). Because of the obvious advantages of this iron color reagent, it was decided to adapt it to the oxidimetric color reaction in which ferrous iron, produced by the reduction of ferric iron by vitamin E (tocopherols), is used as an index