728 



VII. VITAMINS A 



In addition to the review of Hickman^^^ on molecular distillation, an 

 earlier one by Embree^^^ is also excellent. 



COMMERCIAL 



DISTILLATION 



140 160 180 200 220 240 260 



TEMPERATURE OF DISTILLATION 



280 ° C 



Fig. 6. Distillation map ot a fish liver oil: (- -), residual protein odor; ( -) ran- 

 cidity and reversion odor; (— ) free fatty acids; ( — — -) sterols and vitamin D, glyceride 



ethers, and their esters; ( ) preservatives, tocopherols, and their esters; (-0-0-) 



vitamin A and esters; ( A — ^ A) glyceride fats.^^' 



(3) Absorption Spectra 



One of the most useful properties for the identification and quantitative 

 determination of vitamin A is the absorption of light in the ultraviolet por- 

 tion of the spectrum. Vitamin Ai absorbs a broad band in which the maxi- 

 mum effect is obtained at 328 m/i (in chloroform), ^^-^^-^^^ while the maximum 

 absorption in the case of vitamin A2 has been reported at 345-350 m^u.^*'^^ 

 The absorption maximum of vitamin A3, which has been obtained only as a 

 fraction from liver oils, has been given as 285-290 m;u.*'*^ Typical curves 

 for crystalline vitamin Ai, and for neovitamin A are given in Figure 7. 



The wave length at which maximum absorption of vitamin A occurs 

 varies to some extent with the solvent employed. The molecular extinc- 

 tion values for vitamin A in a number of solvents are recorded in Table 12. 



"2 N. D. Embree, Chem. Revs., 29, 317-332 (1941). 



"' F. P. Zscheile and R. L. Henry, Ind. Eng. Chem., A,ml. Ed., I4, 422-425 (1942). 



