Combined assays for vitamins A, D (ergocalciferol), and E in multivitamin preparations with separation by reversed-phase partition chromatography.

A rapid method was developed whereby vitamins A, D (ergocalciferol), and E in multivitamin products are measured in a common assay sample. The method depends on reversed-phase partition chromatography by which the vitamin alcohols are eluted in separate fractions from a column. Vitamins A and E are then determined by their UV absorption, while vitamin D is measured colorimetrically with an antimony trichloride reagent. The column consists of diatomaceous earth impregnated with dimethyl polysiloxane, with n-heptane as the immobile solvent, and 90% methanol followed by 95% methanol as the mobile solvents. Vitamins A and D elute in that order in the 90% methanol, and finally vitamin E elutes in the 95% methanol fraction. The method is widely applicable to various types of multivitamin and vitamin-mineral products including oil-based, water-based, and dry formulations.