. 87 - 



between the components of mixtures usually increases the separabilityo 

 Variation of the solvent often results in unpredictable variation of 

 the chromatographic sequence and of the separability^. 



Functions of the Sorbent 



Like the solvent, the sorbent also plays three critical roles. 

 It exhibits selective affinity for the components of the mixture, it i 

 permits dynajiiic, reversible sorption of each component of the mixture, 

 and it equalizes the flow of the solvent through the column thereby 

 providing uniform, symmetrical zones. 



The sorption of solutes at an interface between a solution and 

 a solid as utilized for the separation of chloroplast pigments is ex- 

 ceedingly complexo The sorptive properties of the sorbent, including 

 the sorption capacity, the selectivity or the resolving power, and 

 certain deleterious effects on sorbed substances, vary with the com- 

 position and treatment or activation. As shovm by the studies with 

 activated magnesia, not only the capacity for adsorption but also the 

 quality of the adsorption vary with the conditions of activation-^' ^5„ 

 For example, the adsorption capacity of magnesia for carotenes increases 

 with the time and temperature of calcination approaching a high level, 

 but the capacity of the magnesia to alter the carotenes increases even 

 more with continued activation. 



The method employed to pack the chromatographic column and the 

 filtration properties of the column depend upon the properties of the 

 sorbento Powders that are compressible may be pressed into the tubes 

 with plungers but slightly smaller than the tubes themselves. This 

 method is particularly effective with powdered sugar, powdered cellu- 

 lose, Celite, and mixtures of Celite with various finely powdered 



