Forced flow planar chromatography

Chromatographic plates can be connected for both capillary-controlled and forced-flow planar chromatography (FFPC), i.e. irrespective of whether capillary action or forced-flow is the driving force for the separation. The first technique is denoted as grafted planar chromatography (31), while the second is known as long distance (LD) OPLC, which uses heterolayers (32, 33). 

SERIALLY CONNECTED MULTILAYER FORCED-FLOW PLANAR CHROMATOGRAPHY... 

Morita, K., Koike, S., and Aishima, T., J. Planar Chromatogr., 11, 94-99, 1998. Nyiredy, Sz., Systematic method development in classical and forced-flow planar chromatography, in Proc. Int. Symp. on Planar Separations, Planar Chromatography 2001, Nyiredy, Sz., Ed., Research Institute for Medicinal Plants, Budakalasz, 2001, pp. 137-148. 

L. Botz, Sz. Nyiredy, E. Wehrli and O. Sticher, Applicability of Empore TLC sheets for forced-flow planar chromatography. I. Characterization of the silica sheets , J. Liq. Chromatogr. 13 2809-2828 (1990). 

Fernando, W. P. N., Larrivee, M. L. and Poole, C. E, 1993. Investigation of the kinetic properties of particle-loaded membranes for the solid-phase extraction by forced flow planar chromatography. Anal. Chem., 65 588-595. 

Novel analytical techniques such as forced-flow planar chromatography (FFPC) and optimum pressure laminar chromatography (OPLC) are other additions to ever-refined tools for separation on a preparative scale, wherein small amounts of complex mixtures may be separated more efficiently on thin-layer chromatography plates operating at fast medium-pressure development with continuous collection of mobile phase at the end of chromatographic plates (Nyredy, 20(X), 2003). 

Nyiredy, S., Progress in forced flow planar chromatography, J. Chromatogr. A (2003) 1000(1-2), 985-999. 

Forced-flow development. Forced-flow planar chromatography is a development technique wherein pressure is used to aid the mobility of the developing solvent. Examples of this are over-pressure layer chromatography (OPLC) and over-pressure thin-layer chromatography (OPTLC). In the latter a forced-flow technique is used to decrease the development time and thus speed up the separations. A pump controls the speed of the mobile phase. Theoretically, this method is faster than when movement of the solvent is due to capillary action alone (normal TLC) and can be used to advantage if slow-moving viscous solvents are involved as developing solvents. 

Delvordre, P. Reynault, C. Postaire, E. Vacuum planar chromatography (VPC) A new versatile technique of forced flow planar chromatography. J. Liq. Chromatogr. Relat. Technol. 1992,75(10), 1673-1679. 

Mobile-phase velocity is higher with forced-flow development than in capillary-flow TLC. The actual flow rate is influenced by the type of chamber (rectangular or sandwich, saturated or unsaturated), the pressure and solvent viscosity (OPLC), or the rotational speed (RPC) (Nyiredy et al., 1988a). Nyiredy (1992) discussed the relation among resolution, separation distance, and time for forced-flow planar chromatography compared to capillary flow. It was stated that for separation of nonpolar compounds by FFPC on silica gel, a separation time of 1—2.5 min over a separation distance of 18 cm can be used without great loss in resolution. By contrast, longer separation times are needed for separation of polar compounds. 

Botz, L., Dallenbach-Toelke, K., Nyiredy, Sz., and Sticher, O. (1992). Characterization of band broadening in forced flow planar chromatography with circular development. J. Planar Chromatogr.—Mod. TLC 5 80-86. 

Forced-flow planar chromatography (FFPC) with the use of external pressure (overpressured layer chromatography, OPLC) or centrifugal force (rotation planar chromatography, RPC) can be used for off-line or on-line PLC (Mincsovics et al., 1988 Nyiredy, 1990). In off-line FFPC, the procedures after development... 

Variations of planar chromatography, where the layer is sandwiched between two counter surfaces and the mobile phase is pumped through the enclosed layer, have been described as OPTLC, OPLC (1), HPPLC (2), and FFTLC (3). In another variation of forced flow planar chromatography the mobile phase is accelerated by centrifugal action (see Chap. 11). An overview of forced flow planar chromatography is given in Chapter 7. 

The optimum migration distance can be deHned as the point beyond which the directional migration of the analyte caused by capillary flow of the mobile phase, resulting in resolution, starts to become overrated by the nondirectional migration caused by diffusion. This explains why the separation distance in TLC can not be extended deliberately as is possible in column chromatography. It should be mentioned here that in forced flow planar chromatography the separation distance can be extended which is the main merit of the OPLC technique. 

---