Vitamin comparative potencies

Note The international unit of vitamin E is equal to one mg of standard eff-o-tocopheryl acetate. The d-form is more active 1 mg = 1.36 I, U. J- -Tocopheryl acetate has 42% of rhe activity of d-o- -rocopheryl acetate in the rat hemolysis test. Based on this activity a potency ratio of 1.4 1.0 for d-a-tocophery] acerate compared to dl-a-tocopheryl acetate has been established. 

In the presence of vitamin A the vitamin may be extracted with organic solvent either directly or after saponification with ethanolic potassium hydroxide. Both vitamins Dg and D3 have identical spectra with broad bands having maxima at 265 m in hexane but the extinction coefficients in this solvent are comparatively low, being 459 for and 474 for D3, and the more intense absorption of vitamin A, with its peak at 328 m//, may completely overshadow the absorption of vitamin D. The spectro-photometric method therefore requires separation of vitamin D from vitamin A and other absorbing materials and can only be applied to comparatively high-potency materials. 

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