146 



CHROMATOGRAPHY 



tribute any uneven settling. After a short time the sugar will have settled 

 as much as it will, and the remaining petroleum ether will percolate 

 downward through the sugar and out the bottom of the tube. 



Ad 



'■^wS 



Ad 



r-^a 



1,2,3,41 





2,3,4 





(a) 



(b) 



(c) 



Fig. 11-1. A series of chromatograms at different stages of develop- 

 ment. In a, the adsorbent (Ad) has settled, leaving a layer of 

 solvent (S) on top. A little later (tube b) this layer of solvent has 

 percolated through the adsorbing material. In tube c, a mixture of 

 four colored materials has been added, and has begun to move into 

 the column. In a few minutes (d), developing solvent has been 

 added, and solute 1 is moving away from the other materials. The 

 finished chromatogram (e) shows four separate bands which may 

 be recovered by slicing the column along the dashed lines. Tube f 

 shows one possible result of an unevenly packed column. 



When almost all of the petroleum ether has disappeared from the top 

 of the sugar, the pigment mixture prepared earlier is added by allowing 

 it to flow slowly down the side of the tube from a pipette. It is unwise 

 to add too much of the mixture, and usually a layer about 1 cm thick 

 is about right. The mixed pigments and solvent will percolate into the 

 upper layers of the sugar column. 



When most of the pigment mixture has moved into the top of the 



