IV. DETERMINATION 95 



see Zechmeistcr,"' Zscheile," also Karrer and Jueker'^). Nowadays the 

 quantitative determination is performed exclusively by spectrophotometry, 

 measuring the molaric extinction coefficient at a maximum of the absorp- 

 tion. For clinical assay and in older works, however, it is frequently carried 

 out either colorimetrically agahist standard carotene,^'' azobenzene,'* or 

 potassium bichromate,-' as well as photometrically. The Zeiss-Pulfrich {pho- 

 tometer with filter S43 is appropriate for the last-named method. ^^ 



From what has been said above, it follows that for the exact investigation 

 of material containing provitamins A a special procedure must be developed 

 in each case; often only a slight modification is needed. Thus the methods 

 quoted here frequently should serve only as guides. From the great number 

 of methods proposed the folIo\Aing will be selected as being either very spe- 

 cial or possessing a relatively broad range of application. The procedure of 

 Fujita et al.^^ is a direct continuation of the well-known method of Kuhn 

 and Brockmann.^ As described by the authors, it is not suitable for vege- 

 tables rich in fat and wax or for leavened green fodder. Zscheile and Whit- 

 more** have elaborated a rather exact method for carotene in fresh and 

 dried alfalfa. The determination of carotene and lycopene in lycopersicon 

 species and strains was carried out by Zscheile and Porter.''^ Further state- 

 ments concerning the carotene content in vegetable tissues have been 

 made by a number of research workers,''^-^^ According to White and 

 Zscheile^^ the distribution of /3-carotene, cryptoxanthin, and zeaxanthin 

 between hexane, aqueous methanol, diacetone alcohol, and 2-methylpen- 

 tanediol-(2,4) makes it possible to separate these pigments. A determina- 

 tion in material rich in fat, e.g., vitaminized chocolate, is given by Vastagh.^ 

 The same communication contains a prescription for the estimation of the 

 cryptoxanthin content. 



4. Determixatiox of Vitamin A and Provitamins A Concurrently 



A simultaneous determination of vitamin A and provitamins A becomes 

 necessary in clinical assays and also when butter, milk, eggs, and artificially 



" F. P. Zscheile and J. W. Porter, Anal. Chem. 19, 47 (1947). 



" World Health Organisation Tech. Rept. Ser. 30, (1950). 



75 M. E. Wall and E. G. Kelley, Ind. Eng. Chem. Ayial. Ed. 15, 18 (1943). 



" H. L. Mitchell and S. M. Hagne, J. Biol. Chem. 164, 543 (1946). 



" H. L. .Mitchell and H. H. King, Anal. Chem. 20, 637 (1948). 



" R. E. Silker, W. G. Schrenk, and H. H. King, Ind. Eng. Chem. Anal. Ed. 16, 513 



(1944). 

 " W. A. G. Nelson, Analyst 72, 200 (1947). 

 80 H. L. Mitchell, Plant Physiol. 24, 323 (1949). 

 8' A. Sreenivasan and R. M. Vaidya, xinal. Chem. 20, 720 (1948). 

 ^2 O. Hromatka and R. Kerl, Monatsh. Chem. 78, 139 (1948). 

 83 J. W. White and F. P. Zscheile, J. Am. Chem. Soc. 64, 1440 (1942). 

 8^ G. Vastagh, Z. Untersuch. Lebensm. 86, 393 (1943). 



