- 95 - 



of zeaxanthin, magnesia attracts the two isolated double bonds in 

 lycopene about as strongly as it attracts the two hydroxyl groups in 

 zeaxanthin. Zeaxanthin and lutein, which differ from each other only 

 in the n\imber of conjugated double bonds, are readily separable in 

 columns of magnesia but not in columns of sugar or of Celite, As 

 zeaxanthin and lutein are comparable, dihydroxy derivatiyes of (?)-caro- 

 tene and Oi,-carotene, these obser-vations indicate that powdered sugar" ^ 

 attracts the hydroxyl groups of lutein and zeaxanthin but not the con- 

 jugated systems of double bonds. Magnesia, by contrast, attracts the 

 hydroxyl groups, the conjugated double bonds, and the isolated double 

 bondSo For each combination of sorbent and solvent, the sorbability 

 of an organic molecule is the summation of the sorbability of the 

 functional groups. 



The conclusions just eniimerated have provided several important 

 practical implications. A sorbent for the resolution of mixtures of 

 similar molecules should attract preferentially those groups or struc- 

 tural \inits that differ most. The more complex the molecule, however, 

 the smaller the variation of sorbability caused by a particular group. 

 From this standpoint, chromatographic methods do not permit the segre- 

 gation of complex organic molecules in relation to particular functional 

 groups as the specific chemical methods do. All these variable circum- 

 stances must be considered when chromatographic sequences are utilized 

 as a guide to the determination of molecular structure. 



The observations summarized in Table IV, III and many of those 

 reported in Lectures I, II, and III show that variation of the chroma- 

 tographic sequence produced by variation of the sorbent and the solvent 

 is frequently an aid in the separation of mixtures. For the separation 



