Preparative thin layer chromatography

TLC can be scaled-up and used for the isolation of large (10-100 mg) quantities of pure component. The practice of the technique is similar to that for analytical, qualitative scale work. The main difference lies in the plates used. Almost all preparative scale work is carried out, in the adsorption mode, principally on silica gel plates of varying thickness, 1-5 mm, and of 20 x 20 cm dimensions. The sample is applied as a streak, either by a pasteur pipette, syringe or a motorised streak applicator . Advantage can be taken of multiple development techniques, which allow efficient separation of components of markedly different polarities. Bands incompletely resolved can be applied to a fresh plate and rechromatographed with a suitable solvent and development procedure. Once development is complete the bands of component can be scraped off with a razor blade or spatula and the component washed off the adsorbent with a suitable solvent. Plates for preparative chromatography are available with added fluorescent indicator which facilitates non-destructive location of the components. The fluorescent indicator is irreversibly bound to the silica. 

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The aporphinoid alkaloid PO-3 (129) was also prepared by intermolecular benzyne cycloaddition between 1-methylene isoquinolines 148 and arynes derived from 147 (Scheme 53). The alkaloid was finally isolated by means of preparative thin layer chromatography (91JOC2984). 

The bacteriochlorin 10 (65 mg, 0.11 mmol) was dissolved in coned H2S04 (18 mL) and allowed lo react at 20 C for 5 min. The mixture was poured into ice, diluted with H20 and NaOAc (7.5 g, 91 mmol) was added. The mixture was extracted several times with CHC13, the organic extractions were washed with H20 (2 x), dried (Na2S04) and evaporated. Preparative thin-layer chromatography (silica gel) gave 11 and 12 yields 10.7 mg (17%) and 44 mg (70%), respectively. 

A dimer portion can be prepared exclusively from the mixed crystal by controlling the wavelength of irradiating light (>410nm) and isolated by preparative thin-layer chromatography. The high-performance liquid chro-... 

Touchstone, J.C. and Dobbins, M.F., Preparative thin layer chromatography, in Practice of Thin Layer Chromatography, John Wiley Sons, New York, 1978, chap. 12. Nyiredy, Sz., Ed., Planar Chromatography, A Retrospective View for the Third Millennium, Springer Scientific, Budapest, 2001. 

Sherma, J. and Fried, B., Preparative thin layer chromatography, in Preparative Liquid Chromatography, Journal of Chromatography Library, Bidlingmeyer, B.A., Ed., Vol. 38, Elsevier, Amsterdam, 105-127, 1987. 

Wing, R.E. and BeMiller, J.N., Preparative thin layer chromatography, in Methods in Carbohydrate Chemistry, Whistler, R.L. and BeMiller, J.N., Eds., Academic Press, New York, 1972, pp. 60-64. 

To obtain reliable chromatograms in the final step of the determination of the analytes by LC or GC, it is important to remove interfering signals resulting from coelution of other compounds. To this end, a variety of techniques are applied for cleanup of the sample extract. The most effective procedures for sample cleanup for PAH measurements are partitioning between M, N-dimethylformamide/water/cyclo-hexane and LC on silica and on Sephadex LH 20. Other cleanup procedures include LC on alumina or XAD-2 and preparative thin-layer chromatography. 

Figure 1. Column and preparative thin layer chromatography.

Seifert, W.K. Teeter, R.M. Preparative Thin-layer Chromatography and High Resolution Mass Spectrometry of Crude Oil Carboxylic Acids, Anal. Chem. 1969, 41, 786. 

Although the metabolism of several phthalate esters has been studied in vitro, essentially all of the in vivo studies have involved DEHP. A summary of these experiments which involved exposure offish to aqueous - C-DEHP is presented in Table IV (11,12). Tissue C was isolated and separated into parent and the various metabolites by preparative thin layer chromatography on silica gel. Metabolites were hydrolyzed where appropriate and identified by gas chromatography-mass spectroscopy. In whole catfish, whole fathead minnow and trout muscle, the major metabolite was the monoester while in trout bile the major metabolite was the monoester glucuronide. The fact that in all cases the major metabolite was monoester or monoester glucuronide despite the differences in species, exposure level and duration, etc. represented by these data, suggests that hydrolysis of DEHP to monoester is important in the biotransformation of DEHP by fish. 

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%,... 

The borohydride reduction of 2 - and 3 -ketocytidine derivatives having or lacking an N4-acetyl group provided a facile route to cytosine nucleosides labeled with tritium at specific positions of the sugar.28 Reduction of either 20a or 20c with sodium borohydride in ethanol-benzene afforded the arabino and the ribo derivatives in the ratio of 4 1. Treatment of the reduction mixture with methanolic ammonium hydroxide gave the deacetylation products, 82b and 19b, isolated in crystalline form by preparative, thin-layer chromatography. 

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