The spectrophotometric determination of vitamin D in fresh-water fish liver oils

Abstract

There are many difficulties associated with the determination of vitamin D, especially in natural products such as fish liver oils. Vitamin A is the chief interfering material; it masks the absorption of vitamin D both in the ultraviolet region and in the antimony trichloride colour test, making the determination of vitamin D almost impossible. In addition to vitamin A₁, fresh-water fish liver oils contain vitamin A₂, which also interferes in direct spectrophotometry. A method for determining vitamin D is described, in which vitamins A₁ and A₂ are eliminated by converting them to anhydro-vitamins A₁ and A₂ and separating them from vitamin D by chromatography on an alumina column.