Estimation of Vitamin A

Abstract

EARLY in 1937, the results of biological and spectroscopic tests for the vitamin A content of a specimen of halibut liver oil and of a concentrate prepared from it were published in NATURE¹. Ten laboratories participated in this co-operative experiment. It was hoped that by enlisting so many groups of workers the uncertainty of the biological results, due to the error inherent in the biological technique, would be minimized, and that an authoritative pronouncement could be made on the magnitude of the value for the conversion factor relating the results obtained by spectrophotometric and biological methods. As a result, a value of 1,470 was reported for the halibut liver oil, whilst that for the concentrate was lower, lying between 1,000 and 1,200. Spectroscopic control carried out on the materials distributed for the feeding tests indicated a satisfactory degree of stability for the oil, but the concentrate deteriorated during the period occupied in the work by an amount sufficient to account for the lower value.