Automated multiple development solvent strength gradients

The basis of automated multiple development (AMD) is the use of different modes of multiple development in whieh the mobile phase eomposition (5j and Sy values) is ehanged after eaeh, or several, of the development steps. Figure 8.11 illustrates the prineiple of AMD employing a negative solvent-strength gradient (deereasing 5-p values). 

Two-dimensional separations in planar chromatography are rather trivial to perform. All unidimensional multiple development techniques employ successive repeated development of the layer in the same direction, with removal of the mobile phase between developments. The main variants are multiple chromatography and incremental multiple development. The basis for automated multiple development (AMD) is the automation of unidimensional, incremental, multiple development with a reverse solvent strength gradient [998]. 2D TLC finds limited use, and is mainly a qualitative technique. 

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