- 103 - 



The chromatographic systems have also been varied with respect to 

 the geometrical pattern of the sorbent, With paper, partioularly-j it 

 has been possible to carry out radial migration and two-way migration 

 which improve the definition and separation of the zones. 



With suitable combinations of sorbent and solvent, extremely small 

 quantities or traces of substances may be separated from mixtureso 

 These separations may be made even vihen the nature of the substances is 



o 



unknown and when the presence of the trace components is unsuspected o 



SEPARATION AND DETECTION 



Selection of Systems 



The selection of chromatographic systems depends upon a large n\m= 

 ber of variable conditions and upon the objectives of the operatoPo 

 For a particular separation, various combinations of solvent and sorbent 

 may be employed. Separations may be made on a macro or a micro scale. 

 They may be employed for comparative tests, for descriptive purposes, or 

 for qualitative and quantitative estimations „ For many of these object 

 tives, special methods must be utilized for the detection and estimation 

 of the separated substances, and these must be selected in relation to 

 the chromatographic system and vice versa. 



Detection, Esti mation, and Comparison of Separated Substances 



Many techniques have now been developed for the location and esti= 

 mation of substances separated in chromatographic systems,, As demon^ 

 strated with pigments, the separated substances may be located in 

 effluent from the sorptive system, in the system itself, or in extracts 

 from successive portions of the system. 



