Development techniques circular chamber

The advantage of the use of linear horizontal development is the reduced developing time. In this case the gravitation does not decrease the mobility of the mobile phase more than in the traditional linear ascending development. Plates are placed horizontally in the chamber and the transport of the eluent is assured by a glass frit strip, a capillary split or any other method. Circular development techniques employ circular TLC plates, the mobile phase enters the centre of the plate and the development occurs out of the centre of the plate. The sample can be applied either onto the dry layer or onto the layer under the flow of the mobile phase. 

Figure 8.19 illustrates another example of the versatility of multidimensional OPLC, namely the use of different stationary phases and multiple development ("D) modes in combination with circular and anticircular development and both off-line and on-line detection (37). Two different stationary phases are used in this configuration. The lower plate is square (e.g. 20 cm X 20 cm), while the upper plate (grey in Figure 8.19) is circular with a diameter of, e.g. 10 cm. The sample must be applied on-line to the middle of the upper plate. In the OPLC chamber the plates are covered with a Teflon sheet and pressed together under an overpressure of 5 MPa. As the mobile phase transporting a particular compound reaches the edge of the first plate it must-because of the forced-flow technique-flow over to the second (lower) stationary phase, which is of lower polarity. 

The different methods of arranging the filter paper in the chromatographic chamber have been applied to sugar separations descending, ascending,39 40 and circular or horizontal development.41 These methods and other techniques will be discussed below. Detailed descriptions of the equipment needed for paper chromatography are readily available.8... 

Other special devices, which are of historical interest, include a special chamber for short bed continuous development. In this technique, the plate extends though a slit out of the actual chamber allowing the developing solvent to evaporate. Separation of very similar compounds can thus be achieved at low R values. The U-chamber according to Kaiser was a special device for circular and anticircular HPTLC. 

Circular and anticircular development methods. This technique produces a radial chromatogram which requires special scanners and is generally not used for lipid separation. The principles of these development methods and the names of companies manufacturing chambers for use in such methods are reviewed by Cserhati and Forgacs (1996). 

Sequential RPC (S-RPC) is a special technique in which circular and anti-circular development modes are carried out sequentially in a normal chamber. 

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