Thin layer chromatography preparation

As a rule, chemical methods used in the examination of writing materials require initial preparation of a sample for study. Paper chromatography, thin-layer chromatography and capillary electrophoresis are experimental techniques often applied. These methods lead primarily to separation of the dyes contained in the ink under examination and to the discrimination of ink samples. The techniques are simple to use, require a small amount of sample for examination, are selective and give reproducible results. Their basic disadvantage, however, is the necessity to isolate the ink from the substrate (e.g. paper) on which the examined document has been prepared. Solvent extraction of the ink often leads to partial damage of the document. 

Compared to paper chromatography, thin layer is more versatile, faster and more reproducible. It is often used as pilot technique to quickly determine the complexity of a mixture. It may otherwise be used as an aid in order to find out the best conditions for large-scale chromatography. Because of its speed and simplicity, it is often used to follow the course of reactions. Thin layer technique has often been used to identify drugs, contaminants and adulterants. It has also been widely used to resolve plant extracts and many other biochemical preparations. 

Other major chromatographic methods, e.g., conventional column chromatography, thin-layer chromatography, and gas-liquid chromatography as well as conventional detection systems, e.g., fluorescence and the UV-VIS absorption of the retinoids themselves or of their colored products, have been used for many years. In these cases developments generally have focused either on special applications, on the simplification of procedures, on improvements in the preparation and stabilization of reagents, or on increased sensitivity. 

The nitration of the 2-anilino-4-phenylselenazole (103) is much more complicated. Even careful nitration using the nitrate-sulfuric acid method leads to the formation of a mixture of variously nitrated compounds in an almost violent reaction. By the use of column chromatography as well as thin-layer chromatography a separation could be made, and the compounds could be partly identified by an independent synthesis. Scheme 33 shows a general view of the substances prepared. Ring fission was not obser ed under mild conditions. 

Until separation techniques such as chromatography (28,29) and counter-current extraction had advanced sufficientiy to be of widespread use, the principal alkaloids were isolated from plant extracts and the minor constituents were either discarded or remained uninvestigated. With the advent of, first, column, then preparative thin layer, and now high pressure Hquid chromatography, even very low concentrations of materials of physiological significance can be obtained in commercial quantities. The alkaloid leurocristine (vincristine, 22, R = CHO), one of the more than 90 alkaloids found in Catharanthus roseus G. Don, from which it is isolated and then used in chemotherapy, occurs in concentrations of about 2 mg/100 kg of plant material. 

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. 

DETERMINATION OF ASCORBIC ACID IN POLYVITAMIN PREPARATIONS BY ION-PAIR THIN LAYER CHROMATOGRAPHY... 

Zinc dust (35 mg) is added to a solution of 9a-bromo-5a-androstan-ll-one (225, 13 mg) in anhydrous ether (2 ml) and acetic acid-OD (0.5 ml, prepared by heating an equimolar mixture of acetic anhydride and deuterium oxide) and the resulting suspension is stirred at room temperature for 4 hr. (The progress of the reaction can be checked by thin layer chromatography.) The... 

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). 

Nonionic surfactants, including EO-PO block copolymers, may be readily separated from anionic surfactants by a simple batch ion exchange method [21] analytical separation of EO-PO copolymers from other nonionic surfactants is possible by thin-layer chromatography (TLC) [22,23] and paper chromatography [24], and EO-PO copolymers may themselves be separated into narrow molecular weight fractions on a preparative scale by gel permeation chromatography (GPC) [25]. 

Technique of thin-layer chromatography. Preparation of the plate. In thin-layer chromatography a variety of coating materials is available, but silica gel is most frequently used. A slurry of the adsorbent (silica gel, cellulose powder, etc.) is spread uniformly over the plate by means of one of the commercial forms of spreader, the recommended thickness of adsorbent layer being 150-250 m. After air-drying overnight, or oven-drying at 80-90 °C for about 30 minutes, it is ready for use. 

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. 

Extraction and purification of luciferin and luciferase (Viviani etal., 2002a) To isolate luciferin, the lanterns of the Australian A. flava were homogenized in hot 0.1 M citrate buffer, pH 5, and the mixture was heated to 95°C for 5 min. The mixture was acidified to pH 2.5-3.0 with HCl, and luciferin was extracted with ethyl acetate. Upon thin-layer chromatography (ethanol-ethyl acetate-water, 5 3 2 or 3 5 2), the active fraction of luciferin was fluorescent in purple (emission Lav 415 nm when excited at 290 nm). To isolate the luciferase, the cold-water extract prepared according to Wood (1993 see above) was chromatographed on a column of Sephacryl S-300. On the same... 

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