THE ROLE OF THE VAPOUR PHASE IN TLC
Due to the participation of the gas phase, development in most TLC chambers is a three-dimensional process. We have to distinguish chamber saturation (of the tank's atmosphere), and capillary saturation (through the rising solvent). Chambers with sandwich configuration including the linear chamber and the OP outfit are unsaturated (s-u). Differences between chamber types are greatest with solvent mixtures which, in S-u chambers, inevitably demix. Preloading of the layer with solvent vapours changes selectivity (in case of solvent mixtures), always reduces R-f values by 20-40 % and diminishes (R-f)-max beyond which no separation is possible to 0.6-0.8 (formation of a virtual front). The layer can be conditioned locally by preloading gradients which can be achieved with the Vario-KS-Chamber (vapour programming). No general rules can be given whether preloading is advantageous or not for separation. It depends on the solvent and the chamber, and its effect must be understood by the user. The preloading effects also occur with PL layers.
Bibliographic Reference: ADVANCES IN LIQUID CHROMATOGRAPHY, SZEGED (HUNGARY), SEPT. 10-14, 1984 WRITE TO CEC LUXEMBOURG, DG XIII/A2, POB 1907 MENTIONING PAPER E 31642 ORA
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Record Number: 1989123026900 / Last updated on: 1987-01-01
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