The chemical estimation of vitamine E in vegetable oils.

The chemical methods for estimation of vitamin E, recommended in the literature, are all based on the oxidation ofa hydroquinone nucleus which is present in all modifications of tocopherol. This nucleus can either be oxidized in such a way as to give a coloured product, or its reducing power may be measured and hence the quantity of tocopherol calculated. The latter principle is employed in the gold chloride potentiometric method of Karrer & Keller (1938, 1939) and in the colorimetric methods based on the FeCl3-x:o'-dipyridyl reaction of Emmerie & Engel (1938). The method of Furter & Meyer (1939) is not specific; the red colour which develops on treatment of tocopherol with concentrated HNO3 is given also by its biologically inactive oxidation product (Lester Smith & Bailey, 1939). A method of assaying a-tocopherol acetate by hydrolyzing with sulphuric acid and titrating with ceric sulphate, recommended by the British Pharmaceutical Codex (1942), opens new possibilities, but apparently has not yet been applied to the estimations of tocopherol in its natural sources. The gold chloride potentiometric method requires elaborate apparatus, and is more complicated than the a:a'-dipyridyl method, whlch is simple, rapid and accurate ifinterfering substances are removed from the unsaponifiable matter before reagents are applied. In this paper we describe means for preparing suitable extracts to which the a:ao'-dipyridyl reaction can be successfully applied so as to secure results consistent with biological values for natural oils as obtained by other workers (Olcott, 1934; Drummond, Singer & MacWalter, 1935) and with such tests as we have so far performed. Preliminary accounts of the work have already been given (Moore & Tosic, 1943; Tosi6c & Moore, 1944).