Developing chamber

After a chromatogram has been developed the TLC plate is removed from the developing chamber and the status quo is fixed by removing the mobile phase remaining in the layer as quickly as possible. This is properly performed in the fume cupboard so as not to contaminate the laboratory with solvent fumes. If possible the TLC plate should be laid horizontally because then as the mobile phase evaporates the separated substances will migrate evenly to the surface where they can be the more readily detected. A fan or hair dryer (hot or cold air stream)... 

There is no other facet where thin-layer chromatography reveals its paper-chromatographic ancestry more clearly than in the question of development chambers (Fig. 56). Scaled-down paper-chromatographic chambers are still used for development to this day. From the beginning these possessed a vapor space, to allow an equilibration of the whole system for partition-chromatographic separations. The organic mobile phase was placed in the upper trough after the internal space of the chamber and, hence, the paper had been saturated, via the vapor phase, with the hydrophilic lower phase on the base of the chamber. 

Fig. 57 Schematic representation of the relationships between development, chamber saturation and pre-loading with solvent vapors (ace. [8]).

HPTLC plates Sihca gel 60 (Merck). Before apphcation of the samples the layer was prewashed once with the mobile phase and dried at 110°C for 20 min. Before it was placed in the developing chamber the prepared HPTLC plate was preconditioned for 30 min at 0% relative humidity (over cone, sulfuric acid). 

Fig. 2 The steps in the process of thin-layer chromatography that have been instrumentalized and automated to a large degree in the recent past. PMD = Programmed Multiple Development, AMD = Automated Multiple Development, DC-Mat or ADC = Automatic Development Chamber.

More recent chromatogram chambers - e.g. the AMD system (Fig. 11) - only possess a small observation window and this can, if necessary, be covered with a black cloth. Development in the DC-Mat (Fig. 12) or the ADC (Fig. 13) automatic development chambers is carried out entirely in the dark. 

For preparative separation, the mobile phase can be selected by performing preliminary analytieal TLC experiments. In PLC, the chromatographic chamber has to be saturated within 2 h beeause the development of preparative plates is much slower than the analytical development. In the analytical preassay during the selection of mobile phase composition, the chromatographic chamber must be hned with a sheet of filter paper to obtain a saturated atmosphere with mobile phase vapor. Then, the optimized analytical mobile phase can be transferred imchanged to preparative separations in the saturated developing chamber. 

FIGURE 5.24 Developing chambers 20 X 20 cm for classical preparative purpose of some manufacturers (left to right) CAMAG twin-trough chamber and flat-bottom chamber. Desaga standard separating chamber, Analtech chamber. 

Especially for temperature-dependent partition processes, besides temperature-influenced humidity of the vapor phase, a thermostat device is recommended for development. The Baron TEC thermobox 200 and Desaga TEC thermobox respectively (Figure 5.25) can be adapted to suit current development chambers using a variable covering mask. A Peltier element with integrated temperatnre control... 

FIGURE 5.25 Automatic development chamber Desaga TLC thermobox 200. 

FIGURE 5.26 Automatic development chamber Baron TLC-Mat adjustable for preparative purposes. 

FIGURE 6.3 Sequence developing chamber by Buncak 1 — support with mobile phase source (reservoir), 2 — holding frame, 3 — magnet holder, 4 — magnet, 5 — cover plate, 6 — TLC plate, 7 — wick with iron core, 8 — solvent entry. (From Buncak, P., GIT Fachz. Lab. (Suppl., Chromatographie), G-I-T-Verlag, Darmstadt, 3-8, 1982. With permission.)... 

A horizontal developing chamber is also manufactured by CAMAG for plates 10 X 10 cm and 20 X 10 cm [13]. Its application is reported in the literature for analytical separations. Therefore, it is not described here in detail. 

Chromatographic development chambers for analytical pirrposes are commercially available in several different sizes. The most commonly used ones are rectangiflar glass tanks with inner dimensions of 21 X21 X9 cm, and they can be used to develop two plates simultaneously in the preparative scale. Even bigger tanks are available for much larger plates, for preparative layer chromatography. The width of the chamber should be varied depending on the size and the number of plates to be developed. 

The twin-trough chamber. Figure 7.17, is the simplest of the HPTLC developing chambers [193]. It consists of a standard... 

The horizontal developing chamber is a sandwich-type chamber for the. simultaneous development of samples from both ends toward the plate center, or for conventional edge-to-edge development [194]. The mobile phase is transported from the reservoir to the... 

The anticircular development chamber contains many of the features. found in the D-chamber. The plate is developed horizontally, the chamber volume is small, and the vapor phase can be controlled by external means [111]. An outer circle is cut fron... 

The selection of a mobile diase for the separation of simple aixtures may not be a particuleurly difficult problem and can be arrived at quite quickly by trial and error. Solvent systems can be screened in parallel using either several development chambers or a device like the Camag Vario KS chamber, which allows the simultaneous evaluation of a number of solvents by allowing each of these to migrate along parallel channels scored on a single TLC plate [8]. However, whenever the number of components in a mixture exceeds all but a small fraction of the spot capacity for the TLC system, a more systematic method of solvent optimization is required. 

Related to the linear development chamber is the Vario-KS chamber [8,195]. The plate is also developed in the horizontal position in a sandwich configuration. However, this chamber is... 

Figure 7.19 Chronpes 25 overpressure development chamber for forced-flow TLC. The configuration shown is for on-line detection. 

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