A re-examination of halibut-liver oil. Relation between biological potency and ultraviolet absorption due to vitamin A

Abstract

A re-examination of the 2 halibut-liver oils used in the co-operative assays of 1936 shows that the original spectroscopic data required some correction for absorption at 328 m[mu]. by constituents other than vit. A. When such a correction is applied, the conversion factor relating E 1%1cm.328 mu to potency in I.U./g. is raised from 1570 to. 1830, which agrees well with the values of 1770 obtained for crystalline vit. A [beta]-naphthoate and 1820 for cod-liver oil, and justifies a round figure of 1800. The results of fractionation expts. on the oils support the method of correction for irrelevant absorption. The significance of the results with respect to the spectrophotometric assay of vit. A is discussed.