96 VITAMINS A AND CAROTENES 



vitaminized foods are examined. The only method which permits concurrent 

 determination is the chromatographic adsorption analysis. However, par- 

 ticularly in clinical investigations, this is usually not practicable because of 

 small quantities of material. Therefore, in the case of serum, the isolation 

 of the vitamin A and the carotenes in pure state is usually avoided. The 

 proper determination is made by means of the blue color with antimony 

 trichloride in pure chloroform. Human serum contains vitamin A and 

 carotenoids with small proportions of carotene, whereas the serum of cattle 

 contains relatively small amounts of vitamin A and is rich in quantities of 

 carotene. As carotenoids also react upon antimony trichloride with a blue 

 color, conditions are complicated and corrections become necessary. Hence 

 it appears that, according to Gillam and Senior^^ and Willstaedt and With,^^ 

 the carotenoids have to be separated by partitioning between petroleum 

 ether and methanol. In the case of human serum, however, a correction is 

 necessary even then because up to 50% of the total carotenoids may be 

 hypophasic. Boyer et al}"^ perform the separation by precipitation of the 

 carotene from alcoholic solution by diluting to 50 to 60%; hereby the vita- 

 min A remains dissolved. This method is especially suited for sera rich in 

 carotene. Willstaedt and With^^ worked out a photometric method which 

 uses as a measure for the correction of the vitamin A value the ratio of the 

 extinctions between the measurements with filter S61 (Pulfrich photometer) 

 after adding antimony trichloride and with filter S43 without such addi- 

 tion. Of great importance for the quantitative determination of vitamin A 

 and carotene is the mode of extraction applied, especially for serum. Both 

 components are combined with protein which must be denaturated. 

 Yudkin^^ and Glover et al.^^ precipitate with alcohol and extract with pe- 

 troleum ether (protein precipitation method), whereas Lindquist^^ as well as 

 Nylund and With'- saponify with alkali and extract afterwards (saponifica- 

 tion method). Further works deal with the examination of blood and 

 serum.'*' '* Veldman'^ reports a microdetermination method. Sobel and 



86 A. E. Gillam and B. J. Senior, Biochem. J. 30, 1249 (1936). 



86 H. Willstaedt and T. K. With, Hoppe-Seyler's Z. physiol. Chem. 253, 133 (1938). 



87 P. D. Boyer, P. H. Phillips, and J. K. Smith, J. Biol. Chem. 152, 445 (1944); 

 Biochem. J. 46, 259 (1950). 



88 H. Willstaedt and T. K. With, Z. Vitaminforsch. 9, 212 (1939); Biochem. J. 41, 

 97 (1947). 



89 A. M. Yudkin, Biochem. J. 35, 551 (1941). 



9» J. Glover, T. W. Goodwin, and R. A. Morton, J. Biol. Chem. 152, 445 (1944). 



" T. Lindquist, Dissertation, University of Upsala, 1938; Acta Med. Scand. Suppl. 



97, 314 (1938). 

 »2 C. E. Nylund and T. K. With, Vitamine u. Hormone 1, 354 (1941). 

 "3 O. A. Bessey, O. H. Lowry, M. J. Brock, and J. A. Lopez, J. Biol. Chem. 166, 177 



(1946). 

 »* G. H. Wise, F. W. Atkeson, M. J. Caldwell, D. B. Parrish, and J. S. Hughes, J. 



Dairy Sci. 30, 279 (1947); /. Animal Set. 7, 70 (1948). 



