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The New Vitamin a Reference Standard and its Use in Evaluating the Vitamin a Potency of Fish Oils^1,2,

One Figure

Department of Agricultural and Biological Chemistry, The Pennsylvania State College, State College

A comparison has been made of the extinction coefficients and the relative biological potencies of U.S.P. Reference Cod Liver Oil no. 3, the new Vitamin A Reference Standard, crystalline vitamin A acetate, and the International Standard. In addition, 27 representative fish oils have been assayed biologically against these standards and conversion factors calculated. The results obtained in this investigation may be summarized as follows:

1. The extinction coefficients of the vitamin A standards employed were found to be:

(a) U.S.P. Reference Cod Liver Oil no. 3: whole oil — 0.914; unsaponifiable fraction — 0.817.

(b) New U.S.P. Vitamin A Reference Standard: whole oil — 5.24; unsaponifiable fraction — 5.25.

(c) Crystalline vitamin A acetate — 1520.

(d) International Standard (ß-carotene) — 2300.

2. Stability studies conducted with vitamin A and carotene solutions prepared for feeding purposes showed these sources of vitamin A to be stable over a two-week feeding period and during 120-day storage at 5°C., provided the solutions were protected against atmospheric oxidation.

3. A comparison of the relative biological potencies of the Vitamin A Standards indicated that the present U.S.P. unit and the International unit may be considered equal. The U.S.P. unit as represented by the new U.S.P. Vitamin A Reference Standard was found to be 1.36 times as potent biologically as the U.S.P. unit represented by U.S.P. Reference Cod Liver Oil no. 3. The potency of the crystalline vitamin A acetate was found to be 3.045 x 10⁶ U.S.P. units per gram.

4. The conversion factors calculated for 27 representative fish oils (nonsaponifiable fraction) in terms of the present U.S.P. Vitamin A Reference Standard ranged from 840 to 2240, with a logarithmic mean of 1500. Conversion factors for the same oils calculated in terms of U.S.P. Reference Cod Liver Oil no. 3 ranged from 1140 to 3050, with a logarithmic mean of 2040. These mean values (1500 and 2040) indicate the extent of the decrease in potency of the cod liver oil standard, and may suggest a partial explanation for the existing confusion regarding conversion factors. The variability of the conversion factors for the fish oils used in the present study indicates that no one single conversion factor will be readily applicable to all fish oils.

² Some of the data were taken from the thesis of the senior author submitted to The Graduate School of The Pennsylvania State College in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

³ Now associated with Lime Crest Research Laboratory, Newton, New Jersey.

Manuscript received 13 September 1948.