Spectrophotometric Determination of Vitamin A in Fish Oils

Abstract

THE purpose of this note is to show that when the vitamin A content of a fish oil has been determined spectroscopically, the result should be expressed in cigm. vitamin A per gm. of oil. E^{1 per cent}_{1 cm} 328 mμ should also be stated. In this laboratory we have lad experience of the confusion that is rife in commercial transactions and investigational surveys when the results of the spectroscopic estimation of vitamin A in fish oils are expressed in I.U./gm., and we seek the co-operation of chemists in the removal of this source of confusion. E^{1 per cent}_{1 cm} 328 mμ (hereinafter referred to for short as the extinction E) is a physical property of an oil which can be measured to an accuracy of 2 per cent on a suitable ultra-violet spectrophotometer. For the estimation of vitamin A the extinction is taken as proportional to the concentration of vitamin A. The use of the extinction to express vitamin A content has the advantage of an unequivocal meaning for the chemist, but does not convey to dealers or consumers a clear indication of the concentration of vitamin A in the oil.