Developing chambers overpressured

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

Vajda, J., Leisztner, L., Pick, J., and Anh-Tuna, N. (1986). Methodological developments in overpressured layer chromatography. Chromatographia 21 1.32-156. Waksmundzka-Hajnos, M., and Wawrzynowicz, T. (1994). Optimization of the separation of plant extracts with the aid of the horizontal DS chamber. J. Planar Chromatogr.—Mod. TLC 7 58-62. 

A review article by Touchstone (221) included tables listing sources of solid phase extraction columns for sample preparation, sample application instruments, horizontal development chambers, densitometers, radioisotope scanners, and instruments for overpressured, high pressure, and centrifugal TLC. Another article reviewed advances in instrumentalized TLC (222). 

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. 

Empore silica sheet, because of its physical characteristics, cannot used in a conventional chamber system over 5 cm development distance (62). Due to the forced flow OPLC makes a longer development distance and rapid separation possible on this sorbent. This is promoted also by the higher density of sheet caused by overpressure (63). 

Steroids have been extensively investigated using instrumental techniques such as overpressured layer chromatography (2,4,17,34,55), parallel development TLC (56), programmed multiple development [57], and automated multiple development/AMD (58). Each technique has been reported to furnish a significant improvement in separation selectivity in comparison with development in conventional TLC chamber systems. 

During recent years, the problem of optimization of separation techniques in thin-layer chromatography has been tackled in both theoretical treatments (129-133) and in the development of instrumentation (134-136). In overpressured TLC (137) a pressurized ultramicrocham r is used. The essential feature of this chamber system is that, in contrast to the rigid glass plate used in the earlier ultramicrochamber (138,139), the sorbent layer is completely covered by an elastic membrane under external pressure, so that vapor phase above the layer is eliminated. Solvent is admitted into the chamber under overpressure by means of a pump system. This technique essentially combines the... 

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