FISH-LIVER OILS 



513 



Table 109. Unsaponifiable Matter in Cod-Liver Oils. 



Laboratory Analysis 



The U. S. Pharmacopoeia formerly required all vitamin A analyses to be based 

 upon laboratory rat assays. This method is slow and costly and not readily adapt- 

 able to commercial practice. In order to overcome the delay in the determination 

 of the value of livers or oils an instrument has been developed to replace the 

 biological assay with laboratory animals. The assay of livers by use of this instru- 

 ment is rapid and when multiplied by the factor 1,600, the results are sufficiently 

 accurate to be acceptable to the Pharmacopoeial Association in its volume of 

 regulations XIV which has recently been released. The assays for vitamin A by 

 means of the spectrophotometer are now official and generally acceptable for pur- 

 chasers and sellers of oils and concentrates. 



Vitamin A is known to absorb ultra-violet light, and the instrument for the 

 measurement of this absorption is known as a photoelectric spectrophotometer. 

 The amount of light absorbed by a solution of the oil is measured and the vitamin 

 A is calculated. The schematic diagram. Figure 23-6 indicates the optical con- 

 struction of the instrument. There are a number of instruments of different makes 

 available but operate on a similar absorption, which is based on the light absorp- 

 tion faculty of the vitamin A. 



Auto Headlight 



Fig. 23-6. Schematic drawing of operating principles of the photoelectric spectrophotom- 

 eter. 



