PROPERTIES OF THE CAROTENOIDS 653 



single substance was actually composed of two fractions: a- and /3-caro- 

 tene. Karrer and Walker'"^ were the first to employ calcium oxide in place 

 of calcium carbonate as an adsorbent for the separation of carotene. The 

 development of an understanding of the stereoisomers of carotenoids by 

 Zechmeister and his co-workers was to a considerable extent based upon 

 this application of chromatography. 



Reviews on chromatography include the early work of Winterstein,^!^ 

 and the more recent ones of Zechmeister,"'^ Cook,^'^ and Koschara.''* 

 The most complete treatment of the subject is given in the admirable 

 treatises of Zechmeister and v. Cholnoky.^'^-^" Another excellent mono- 

 graph is Chromatographic Adsorption Analysis, by Strain. ^^^ In 1947 

 Williams*'^ published a shorter treatise which includes some of the more 

 recent developments in the field. The latest contribution to the subject 

 is the book by Cassidy.^'*" 



a. Applications of the Chromatographic Technic. There are a num- 

 ber of problems which can be solved by the use of chromatographic 

 methods and for which no other procedures are available. 



One important use is for testing the homogeneity of a product. If a 

 substance cannot be broken up into two or more components Avhen solu- 

 tions of it are percolated through an adsorption column, the material is 

 chromatographically homogeneous. Although this is not an absolute proof 

 of genuine chemical purity, it is at least presumptive evidence. The 

 amount of the adsorption affinity depends to a much greater extent upon 

 molecular structure than do such properties as melting point, boiling point, 

 solubility, or even spectral absorption. It is conceivable, however, that 

 two substances might have an identical adsorption coefficient and so not be 

 resolvable into their separate components on the Tswett column. Such a 

 condition can be excluded, however, if one finds a single zone when the 

 material is chromatographed in several solvents. Tswett^^' points out 

 that it is extremel}' unlikely that the adsorption isotherms of two sub- 



*'2 A. Winterstoin, Fralctionierung unci Reindarstellung von Pflanzenstoffen nach dem 

 Prinzip der chromatographischen Adsorptionsanalyse, in G. Klein's Handbuch der Pfianz- 

 enanahjse, \q\. IV, Part 2, 1403-1437, Springer, Vienna, 1933. 



5'3 L. Zechmeister and L. v. Cholnoky, Motiatsh., 68, 68-80 (1936). 



51^ A. H. Cook, Chemistry & Industry, 14, 724-726 (1936). 



5'5 W. Koschara, Z. physiol. Chem., 239, 89-96 (1936). 



^'* L. Zechmeister and L. v. Cholnoky, Die chromatographische Adsorptionsmethode , 

 Grundlage, Melhodik, Anwendungen, Springer, Vienna, 1937. Principles and Practice of 

 Chromatography, translated from the second and enlarged German edition by A. L. 

 Bacharach and F. A. Robinson, Wiley, New York, 1941. 



*" L. Zechmeister, Progress in Chromatography, 1938-1947, Chapman & Hall, London, 

 1950. 



*■* T. I. Williams, .1/; Introduction to Chromatography, Chemical Pub. Co., Brooklyn, 

 1947. 



*'*" H. G. Cassidy, Adsorption and Chromatography, Interscience, New York, 1951, 

 360 pp. 



