Preparative layer chromatography development

Modem planar chromatography is suitable not only for qualitative and quantitative analysis but also for preparative purposes. The separation efficiency of a thin-layer chromatographic system is independent of this intended purpose and is mainly determined by the quahty of the stationary phase, that is to say, by the applied coated layer. Therefore, progress in modem planar chromatography can be attributed not only to the development of the efficiency of the instmments but also to a large extent to the availability of high-quahty precoated layers. And today, as in the past, bulk sorbents for self production, especially of preparative layer chromatography (PLC) layers, are widely used. 

Chromatographic development chambers for analytical pirrposes are commercially available in several different sizes. The most commonly used ones are rectangiflar glass tanks with inner dimensions of 21 X21 X9 cm, and they can be used to develop two plates simultaneously in the preparative scale. Even bigger tanks are available for much larger plates, for preparative layer chromatography. The width of the chamber should be varied depending on the size and the number of plates to be developed. 

Preparative layer chromatography (PLC). Minor constituents were isolated by PLC on a glass backed plate developed twice in hexane-isopropanoi (9 1, v/v). Bands were detected under UV at k254 nm and the compounds were eluted from scraped sections of the silica gel with CHCl3-MeOH (19 1). 

Other variations have been described by Szepesi and Nyiredy (1996) and Nyiredy (1996). Incremental multiple development (IMD) (Szabady et al., 1995 and 1997) involves rechromatography with the same composition mobile phase for distances that increase, usually by the same amount (linearly). If development occurs in the same direction with the same distance but different mobile phases having distinctive strength and selectivity, the method is termed gradient multiple development (GMD) this method most significantly increases the separation capacity of the system. In bivariate multiple development, the development distance and mobile phase composition are varied simultaneously for successive runs this method, which is effective for samples of differing polarity, has been used especially for preparative layer chromatography plates. 

PTFE membranes loaded with particles of silica gel or chemically bonded silica gel are a relatively new type of flexible support developed for TLC (97-99). These Empore sheets, which are similar to Empore extraction disks used for solid phase extraction (100), are especially useful for recovery of separated samples in preparative layer chromatography or scintillation counting of radioisotopes by cutting out sections of the chromatogram containing the analytes of interest. Empore sheets have lower efficiency than conventional thin layers (29) and have not yet been applied widely for TLC. 

Circular development of TLC plate, 27 Classical preparative layer chromatography (CPLC), 307,308-317 applicability of, 317... 

Gas chromatography (gc) is inferior to hplc in separating abiUty. With gc, it is better to use capillary columns and the appHcation is then limited to analysis (67). Resolution by thin layer chromatography or dc is similar to Ic, and chiral stationary phases developed for Ic can be used. However, tic has not been studied as extensively as Ic and gc. Chiral plates for analysis and preparation of micro quantities have been developed (68). 

One of trends of development of thin-layer chromatography implies that replacement of aqueous-organic eluents by micellar surfactants solution. This is reduces the toxicity, flammability, environmental contamination and cost of the mobile phases, reduce sample prepar ation in some cases. 

Isocratic linear development is the most popular mode of chromatogram development in analytical and preparative planar chromatography. It can be easily performed in horizontal chambers of all types. The mobile phase in the reservoir is brought into contact with the adsorbent layer, and then the movement of the eluent front takes place. Chromatogram development is stopped when the mobile phase front reaches the desired position. Usually 20 X 20 cm and 10 X 20 cm plates are applied for preparative separations, and this makes the migration distance equal to about 18 cm. Due to the fact that the migration distance varies with time according to the equation Z, = (Z, c, and t are the distance of the solvent front traveled, constant,... 

The development of the open-column methods, ie paper chromatography (in the 1940 s) and thin-layer chromatography (in the 1950 s) greatly improved the speed and resolution of lc, but there were still serious limitations compared to modern lc methods, in that analysis times were long, resolution was poor and quantitative analysis, preparative separations and automation were difficult. 

Baker Chemical Co. Molinate sulfoxide was prepared by reacting [ring- Cjmolinate with equimolar m-chloroperbenzoic acid in chloroform (10). The product was puriTied by preparative thin-layer chromatography (TLC) using acetone hexane (1 1) as the developing solvent. The final radiopurity was 98%,... 

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