226 CAROTINOIDS AND RELATED PIGMENTS 



mosphere of .hydrogen converted some of the pigment into a product 

 which still retained the solubility of xanthophyll in ether, giving 

 a yellow solution, but which readily formed an ether-insoluble salt 

 with alkali. 



Willstiitter and Page (1914) state that xanthophyll is incompletely 

 recovered by ether after dissolving in concentrated methyl alcoholic 

 KOH. These facts all point to the possibility of xanthophyll being 

 attacked by alkalis under certain conditions. 



The effect of adsorbents on petroleum ether and carbon disulfide 

 solutions of the xanthophylls is especially characteristic and serves 

 not only to distinguish these carotinoids from the hydrocarbon caro- 

 tinoids but also from each other. Tswett (1906b) has shown that 

 thoroughly dried precipitated calcium carbonate, inulin, sucrose and 

 many other compounds, which are insoluble in petroleum ether, will 

 completely adsorb the xanthophylls when their petroleum ether solu- 

 tion is shaken with an excess of the adsorbent. In order to bring 

 about this adsorption, however, no trace of alcohol must be present, 

 Tswett having shown that petroleum ether containing only one per 

 cent alcohol releases the bulk of the xanthophylls from the adsorbing 

 agent. There is therefore good reason to believe that much smaller 

 amounts of alcohol will interfere greatly with the adsorption. 



While this gross test may serve to distinguish the carotinoids con- 

 taining oxygen from the hydrocarbon carotinoids, the principles in- 

 volved can also be used to analyze further the xanthophylls and 

 even to separate them from each other. The general principle which 

 is thus utilized is that when several substances present in a single 

 solvent are all adsorbed by a single adsorbent, there is more or less 

 replacement of one adsorbed substance by the- others, depending upon 

 the relative affinities of the several substances for the adsorbent, espe- 

 cially if the adsorption compounds in each case are dissociable. This 

 is the principle of Tswett's chromatographic analysis of plant extracts 

 containing chlorophyll and the carotinoids. 



The technic which is used for the analysis of a mixture of caro- 

 tinoid (and chlorophyll) pigments by this method is as follows: A 

 very finely divided adsorbent is selected which will have no oxidizing 

 or reducing or hydrolyzing action on the pigments to be examined. 

 Calcium carbonate is especially recommended. Powdered sucrose 

 is also very suitable. The calcium carbonate is first dried for several 

 hours at 150 C. A glass adsorption tube 1 to 2 cm. in diameter and 

 10 to 15 cm. long is now prepared which is drawn out at one end. 



