Band Application of Substance Solutions

Special techniques are necessary in order to apply larger volumes uniformly and as a narrow start band. A detailed description of the various methods is warranted since this is an important problem in preparative TLC. 

As has been already described [673], a solution can be evenly and rapidly sprayed as a band, using a micro spray gun (Firm 44). The layer on either side of the start band is then best covered (Fig. 21 A). In addition, devices have been developed which permit more uniform application. In this connection, the spreading apparatus for PC, constructed by Mckibbins et al. [414] first comes to mind. The newer commercial Chromatocharger (Fig. 51, Firm 33) functions according 

Note Usually 6—10% solutions are applied in preparative TLC. The solvent must be as volatile and non-polar as possible. If repeated application is necessary, one should wait after each addition imtil the solvent has evaporated. The formation of a chromatogram around the point or band of application, is undesirable. The band should terminate 1—2 cm from each side of the plate. 

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