Analyses of Fat-Soluble Vitamins, XIV. Collaborative Study of the Determination of Vitamin D in Multivitamin Preparations
Abstract The colorimetric assay for the determination of vitamin D (4000—50,000 international units (IU)/g) in multivitamin preparations has been collaboratively studied. The method is based on the same principle as the official method for the determination of vitamin D in concentrates, i.e., elimination of trans-isomers of vitamin D resins. The method includes the following steps: saponification and extraction (isolation of unsaponifiable material), phosphate-treated alumina column chromatography (elimination of tocopherols and vitamin A decomposition products), partition chromatography with polyethylene glycol 600 and Celite (separation of vitamin D fraction from vitamin A alcohol), adsorption chromatography on Florex (elimination of vitamin A decomposition products and small amounts of polyethylene glycol 600), maleic anhydride addition reaction (elimination of trans-isomers of vitamin D resins), and colorimetric determination at 2 wavelengths with and without acetic anhydride (an inhibitor for the color reaction of vitamin D and antimony trichloride). The mean result of 4 laboratories for 8 different samples, expressed as per cent of the known amount of vitamin D added, was 95.8% with a coefficient of variation of 10.5%. Considering the complexity of the method, the collaborative results were reasonable. The method has been adopted as official first action.