Saturation and Equilibration of the Layer

In a closed S-tank (without extra saturation) such equilibration does not take place or has as little an influence as the evaporation effect. The influence of the relative humidity first outside and then within the chamber must always be considered in adsorption-TLC. The TLC-experiments carried out in this connection, using various relative humidities, are impressive (Fig. 24, right) [226]. According to these, it appears necessary to develop thin-layer chromatograms in a moisture chamber in 

On no account must the chambers be exposed to sunlight but should be placed in diffuse daylight. It is advisable in analytical work to cover the inside of the laboratory window with sheets opaque to UV-light (Firm 34) or an equivalent varnish (Firm 141). For the thin-layer chromatography of substances like carotenes which are sensitive to light, the outside of the chamber is covered with black foil or one works in a dark room in red or green light. 

Oxidation of substances on the layer can be prevented by placing a so-called preparation box (Firm 44) over the plate during application and filling it with nitrogen or carbon dioxide. A fine spray of water often averts decomposition at the start point. 

In order to develop chromatograms in absence of oxygen, carbon dioxide is passed into the chamber (as far as the substances allow it) or nitrogen is first swept through it. A cover equipped with tubulure and two-way tap is an advantage here. 

Note the whole breadth of the TLC-plate must dip into the solvent to the same depth, i. e., ca. 0.5 cm, but not so as cover the spots at the start. Mixtures of 

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