= 86 - 



sensitive techniques for the detection and investigation of the sepa- 

 rated substances o 



SOLVENTS AND SORBENTS 



Functions of the Solvent 



In the early investigations of chloroplast pigments, the solvent 

 was found to serve three critical functionso It dissolves the pigments 

 \ in a condition suitable for adsorption. It permits the reversible 

 sorption of the pigments in the chromatographic column, and it facili- 

 tates the selective sorption of the components of the mixture by the 

 sorbento 



The chromatographic experiments with chloroplast pigments showed 

 that the separations are often improved by slight modifications of the 

 solvent,, The addition of weakly polar substances such as alcohols and 

 acetone to nonpolar wash liquids provides an adsorption gradient in the 

 columns It accelerates the separation of the sorbed pigments. It 

 often improves the sharpness or definition of the pigment zones, be- 

 cause it reduces the trailing regions. In this way, it restricts the 

 cross-contamination of the zones, and it facilitates the separation ef 

 the strongly sorbed pigments as well as the separation of the weakly 

 sorbed pigments in columns of a single sorbent, 



VR.th a given sorbent and with a particular pigment mixture, the 

 solvent determines the sorption capacity of the sorbent and the sepa- 

 rability of the mixture. As a rule, sorption is greatest from solu- 

 tions in nonpolar solvents such as saturated hydrocarbons and least in 

 very polar substances such as organic acids and bases '-'o The separa- 

 bility of pigments varies greatly with the solvent and with the addi- 

 tion of various solutes. The addition of substances that are sorbed 



