Thin Layer Chromatography - Coating the Thin Layer Plate 2
The stationary phase (adsorbentor support) is mixed with between 2 and 5% w/w of binder (usually gypsum) and made into a slurry with water. In some cases traces of surfactants or detergents are added to facilitate the spreading. The slurry is poured into the tank as shown in figure 1. The uncoated glass plates that have been carefully cleaned are placed edge-to-edge on a flat conveyer belt under the tank. The thickness of the coating on the plate is determined by adjusting the height of the weir at the front of the plate that allows the slurry to flow under it and onto the plate as the plate moves forward. The plates are usually 25 cm by 25 cm and after coating and drying are cut to widths of 5 or 10 cm or as required. Plates of sizes other than those mentioned are produced but the same procedure is employed.
There are a number of different manufacturers of TLC plates to choose from today, some specializing in particular types for specific applications others merely producing standard silica plates. However, the coating procedure for TLC plates is now well established and appropriate quality control is usually exercised and so plates can be purchased with a reasonable amount of confidence in their reproducibility.