Studies in vitamin A: 4. Spectrophotometric determination of vitamin A in liver oils. Correction for irrelevant absorption.

The ultraviolet absorption spectrum of vitamin A with itsmaximum near 328 m,. was described nearly 20 years ago (Morton & Heilbron, 1928a, b). The intensity of absorption shown at that wave length by a fish-liver oil or concentrate was conveniently expressed in terms of E "lo 328 m,u. (Gillam & Morton, 1929), and this magnitude was early seen to afford a guide to potency. If a number of fish-liver oils covering a fair range of potency was examined in three different ways, namely, (a) by the method of biological assay, (b) by the antimony trichloride colour test, and (c) by the spectrophotometric method, the results showed fair agreement. From a strictly quantitative standpoint the bio-assays were primitive, the colour test was handicapped by