Most of the classical layers were prepared on glass since it was generally available and easily handled. It could be cut to any size and Camag and Desaga made special devices for holding the glass plates and dispensing the slurries. The glass had to have an especially smooth surface and often the edges were smoothed to prevent cuts to the operator's fingers while the plates were handled. Any glass used to prepare the TLC plates must be carefully cleaned to remove any grease or oils that might prevent an even layer from being applied.

Pre-scored plates are discussed above, but any glass-supported plate can be cut by placing it face down on a sheet or two of paper towelling and scoring the glass with a carbide scribe (using a steady, hard motion). The plate is then lifted, held along the two edges with a paper towel, and broken, using a combination of bending (away from the score) and a pulling apart to break the plate. A final step is to remove any loose silica (or other sorbent) from the newly cut edges with a paper towel. This prevents edge effects - faster movement of the solvent at any rough, sorbent edges.

With special automated equipment, some manufacturers began to use both aluminium and polyter-phthalate plastic supports. Generally, thinner layers were found to be optimal on these flexible layers, but the separations are no different from that found on a glass plate since the other items such as the binder and silica gel are the same. Although most TLC plates sold today are still on glass, some researchers feel that the ability to cut to size or the removal of components after the separation is a distinct advantage. After cutting these plates with scissors or a sharp-bladed instrument, 'edging', discussed above, should be done.

The flexible layers can sag and should be stood in a chamber at a sharper angle (Figure 7) than a rigid glass plate. This is especially true if a chlorinated developing solvent is used. If one of the impregnated or incorporated layers discussed above is used, they require a special holding device or clamps to hang them in the developing chambers, as was used for paper chromatographic separations.

Best positioning

Figure 7 Positioning of flexible-backed TLC plates in a developing chamber.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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