CHAPTER 



11 



Chromatography 



Chromatography is a laboratory technique for separating mixtures of 

 similar materials from each other. A solution of the mixture is allowed 

 to flow with its solvent over the surface of a finely-divided or porous 

 solid material. The different components in the mixture flow at different 

 rates, eventually becoming separated from each other. Chromatography 

 has become popular in biological work because extracts from living cells 

 contain different materials of similar chemical nature. Often the only 

 way to analyze those mixtures is to separate the components from each 

 other. For example, we might break down a protein into the amino 

 acids of which it was constructed. Since all the various amino acids are 

 similar in chemical and physical properties, it may be difficult to study 

 them by ordinary chemical techniques. Chromatography is the most 

 convenient way of separating these amino acids from each other. As a 

 second example, some of the work on the metabolism of cells involves 

 mixtures containing simple sugars and sugar derivatives. Such mixtures 

 also are separated by chromatography. A third example is a separation 

 of the chloroplast pigments of plants. This mixture has been chosen for 

 detailed description because these materials are highly colored, and it is 

 easy to follow the progress of the separation. Several techniques for sep- 

 arating these pigments are described in detail. In a later section, other 

 applications of chromatography are described more generally. 



Chromatography means literally "writing with color." The name was 

 chosen because the method was first developed to separate mixtures of 

 colored compounds. Several different physical principles are involved, 



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