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sorption phenomenon for the resolution of mixtures of all kinds of 

 organic and inorganic ions. 



An important variation of the sorbent first employed with color- 

 less substances was the use of a fixed liquid as the sorptive agent. 

 With these liq\iids fixed on powdered nonsorptive solids, mixtures are 

 resolved by selective partition between the stabilized, nonmobile 

 liquid and a mobile, immiscible liq\iid or gas. This procedure is 

 effective both with organic and inorganic substances'. 



In spite of a prodigious amount of work on the separation of 

 substances by the various modifications of chromatography, there is not 

 as yet a very sound basis for comparison of the effectiveness of various 

 modifications of the method. For the leaf pigments, adsorption in 

 colximns of magnesia provides extensive separation of many carotenoids 

 but produces decomposition of the chlorophylls. Adsorption in columns 

 of sugar provides separation of chlorophylls and many carotenes as shown 

 in Figure 11,1. Partition between petroleum ether and aqueous methanol 



with either solvent fixed in paper provides separations very similar to 



I IQ • I 20 

 those observed in columns of powdered sugar > 7» > „ 



Variations of Chromatographic Systems 



For the resolution of a particular mixture, various combinations 

 of sorbents and solvents may be employed as shown by the observations 

 with chloroplast pigments and as may be inferred from Table IV, IV. 

 Thus far, there are few guiding principles for the selection of solvents 

 and sorbents. Progress is usually based upon analogy and upon empirical 

 tests. 



