CHROMATOGRAPHY 157 



raphy and then can be separated by adsorption, ion exchange, or partition 

 chromatography. Such a range of techniques is in use that it is difficult 

 to say that one method is more commonly used than any other. Paper 

 chromatography of simple sugars is performed on Whatman No. 1 or 

 Schleicher and Schuell No. 589 White Ribbon paper, using the same 

 solvents as for amino acids, or slight modifications thereof. The general 

 reference books listed at the end of the chapter give fairly detailed de- 

 scriptions of various methods and numerous citations of the original liter- 

 ature. 



Lipids: The lipids include fats, waxes, and other materials that dissolve 

 in any of a set of nonaqueous solvents. In the broad sense, the chloroplast 

 pigments are lipids, and, in fact, the chromatographic methods used for 

 lipids in general are only slight modifications of those used for the 

 chloroplast pigments. 



Proteins: The chromatographic separation of proteins, including the 

 enzymes, has been difficult because the molecules are large and do not 

 move freely, the molecular surfaces possess a wide range of chemical 

 and electrical properties, and the proteins themselves are relatively un- 

 stable. Ion exchange methods seem to have produced the best results, but 

 the behavior even on ion exchange columns probably involves some 

 adsorption. Columns of tricalcium phosphate gel and of several Dowex 

 and Amberlite resins are satisfactory for some proteins. A number of 

 materials prepared by a chemical treatment of cellulose have been re- 

 markably successful in the separation of a variety of proteins. These 

 include carboxymethyl-cellulose and DEAE-cellulose (diethylamino- 

 ethyl). ECTEOLA-cellulose (from epichlorohydrin and triethanol- 

 amine) is not as favorable for protein but is a superior material for 

 separating nucleic acids. Most of these materials are now available from 

 biochemical supply houses. 



Paper electrophoresis 



If an electrical field is imposed across a liquid containing charged par- 

 ticles, these particles will migrate in the liquid, negatively charged parti- 

 cles moving toward the positive electrode and positively charged particles 

 toward the negatively charged electrode. This behavior is the basis of 

 a very popular method— known as electrophoresis— for separating ma- 

 terials. Proteins were among the first compounds to be separated this 

 way, and more recendy other materials have been found to be adaptable 

 to the method. 



