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Details of analytical procedures are given for the analysis of vitamin D concentrates, such as resins, powders, and solutions, all without vitamin A. For the analysis a choice had to be made between the potential vitamin D content (the sum of calciferol (D) and precalciferol (P)) and the actual vitamin D content (calciferol only) in partly isomerized solutions. The biological vitamin D assays can only give the potential vitamin D content when both sample and reference standard solutions are equilibrated simultaneously to the same P ⇋ D ratio. Therefore the biological vitamin D unit should be based on the potential vitamin D content. An important point in the chemical assay of vitamin D in concentrates is the prevention of the oxidation of fat-soluble phenolic antioxidants during saponification. These oxidation products of antioxidants inhibit the color reaction. The colorimetric determination becomes more specific after inactivation of tachysterol by the addition of maleic anhydride. A collaborative test was carried out in 3 laboratories with an oil containing 3 different concentrations of vitamin D. The results of this test have verified the correctness of the analytical procedures.

Chemical Analysis of Vitamin D in Concentrates and Its Problems. XII. Analysis of Fat-Soluble Vitamins