Preparation of the Stationary Support

The support medium may be a sheet of cellulose or a glass or plastic plate covered with a thin coating of silica gel, alumina, or cellulose. Large sheets of cellulose chromatography paper are available in different porosities. These may be cut to the appropriate size and used without further treatment. The paper should never be handled with bare fingers. Although thin-layer plates can easily be prepared, it is much more convenient to purchase ready-made plates. These are available in a variety of sizes, materials, and thicknesses of stationary support. They are relatively inexpensive and have a more uniform support thickness than hand-made plates. 

The procedure of paper and thin-layer chromatography. A Application of the sample. B Setting plate in solvent chamber. C Movement of solvent by capillary action. D Detection of separated components and calculation of Rf. 

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Preparation of the stationary phase for reversed-phase chromatography involves a special technique. The stationary support like silica gel, alumina, teflon or kieselguhr used for the purpose is first rendered hydrophobic by exposure to vapours of chlorosilane. This is followed by treatment of the stationary support with the appropriate hydrophobic solvent. This treatment of the stationary support may simply be carried out by immersing it in the hydrophobic solvent of choice alternatively, this step is carried out employing a rotary vacuum evaporator which gives a uniform coating. 

In addition to the development of the powerful chiral additive, this study also demonstrated that the often tedious deconvolution process can be accelerated using HPLC separation. As a result, only 15 libraries had to be synthesized instead of 64 libraries that would be required for the full-scale deconvolution. A somewhat similar approach also involving HPLC fractionations has recently been demonstrated by Griffey for the deconvolution of libraries screened for biological activity [76]. Although demonstrated only for CE, the cyclic hexapeptides might also be useful selectors for the preparation of chiral stationary phases for HPLC. However, this would require the development of non-trivial additional chemistry to appropriately link the peptide to a porous solid support. 

The solution coating technique involves preparing an excess of solution of known concentration of the stationary phase dissolved in appropriate solvent. A known weight of support is then added slowly to a known volume of solution while the solution is stirred until all of the support is in suspension. This slurry... 

Solvent code these solvents have been found to be the most suitable for the preparation of solutions of the stationary phase prior to the addition of support material during the coating process. A = toluene B = dichloromethane C = methanol D = acetone. 

On the other hand, the direct chromatographic approach involves the use of the chiral selector either in the mobile phase, a so-called chiral mobile phase additive (CMPA), or in the stationary phase [i.e., the chiral stationary phase (CSP)]. In the latter case, the chiral selector is chemically bonded or coated or allowed to absorb onto a suitable solid support. Of course chiral selectors still can be used as CMPAs, but the approach is a very expensive one owing to the high amount of chiral selector required for the preparation of the mobile phase, and the large amount of costly chiral selector that is wasted (since there is very little chance of recovering this compound). Moreover, this approach is not successftd in the preparative separation of the enantiomers. 

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