- 121 - 



elements of suitable cross section and half-life^. Physical and bio= 

 logical detection methods have been widely employed, the latter 4ape° 

 cially with antibiotics and growth hormoneso As in chromatography^, 

 the electrochromatographic sequences also serve for the description 

 and identification of various substances-^o Some of the detection 

 methods are illustrated by the figures showing various modifications 

 and applications of the electrochromatographic teohniqueso (See Fig- 

 ures Vj5 ^o VjlOo) 



Conditio ns Required for Electrochromatographic Separations 



Many circumstances affect the separation of mixtures by differ- 

 ential electrical migration, hence the experimental conditions must be 

 controlled and described,, These variable conditions are the composi- 

 tion of the background solution^^^ the temperature, the DC potential, 



12 

 the concentration of the mixture and of extraneous ions in the mixture , 



and the sorbability of the migrating ions by the stabilization mediuml5o 



The composition of the backgroimd solution is usually specified with 



respect to the nature and concentration of the electrolyte and the pHo 



For estimation of the ionic velocity, the temperature and the potential 



must be carefully controlled, but for comparative separations careful 



control is unnecessaryo The DC potential may vary from 5 or 10 volts 



per centimeter to as much as 100 volts o At the high potential, the 



separations take place very rapidly, and the zones of the separated 



substances remain very smalll°o 



The ionic concentration of the mixture itself or of the mixture 



plus extraneous electrolytes should not be much greater than the ionic 



concentration of the background electrolytic solutiono At high 



