Development Chambers

Historically, the majority of TLE experiments have been carried out in the horizontal mode, with solvent reservoirs at both ends of the plate. This set-up continues to be used today by several groups, and is shown in Figure 2. The plates are supported with the chromatographic surface either up or down.

Solvent is transported to and from the plates by wicks, which also serve as electrical contacts. A range of materials has been used as wicks, including filter paper, sintered glass and felt. The electrodes are usually submerged in the solvent and made of an inert conductive material, such as silver, stainless steel, carbon or platinum.

A less popular approach involves the use of vertical plates, with solvent at the base of the plate (Figure 3). Electrical contact is made via the solvent at the base

Figure 2 A horizontal tank design for thin-layer electro-chromatography.

Figure 2 A horizontal tank design for thin-layer electro-chromatography.

Figure 3 A vertical tank design for thin-layer electrochromatography with bottom solvent feed.

and an electrode fixed at the top of the plate. While in such systems the solvent is sometimes described as migrating up the plate because of electroosmosis, this may not always be strictly true. The main limitation of this arrangement stems from the lack of solvent reservoir at the top of the plate, and uneven solvent evaporation from the plate can impart a capillary-driven component to the solvent migration. This makes it difficult to differentiate between electroosmotic solvent flow and capillary solvent flow. Some workers have placed a second solvent reservoir at the top of the plate, and generated elec-troosmosis in a downward direction.

Chambers are usually sealed from the atmosphere in order to provide a solvent-saturated atmosphere, thus reducing evaporation. Some arrangements employ a cover plate, usually glass, in direct contact with the chromatographic surface in order to minimize evaporative effects.

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