Indirect printing techniques

If the compounds to be separated are not visible or UV active and the S-RPC technique has to be used for a certain separation problem, an indirect method can be used to detect the substances in situ on the layer (11). A segment is cut from an aluminum-backed analytical TLC plate and immediately pressed for a few seconds against the wetted preparative layer, to make a copy of the separation. After drying, the analytical plate can be sprayed with a suitable reagent. With the help of this print, the separated compounds can be located on the preparative plate. An example of an S-RPC separation is presented in Figure 19 the location of the separated compounds was indirectly between each of the 12 operating steps. 

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