Alumina thin layer chromatography

A large number of variously 2-, 4-, and 5-substituted thiazoles with alkyl, aryl, hydroxy, methylthio, mercapto, halo, and nitro groups have been analyzed by thin-layer chromatography on silica and alumina by the Stahl s technique (167, 170, 172). Among the many systems recommended for the elution of these compounds are the following ... 

An important publication by Kost et al. (63JGU525) on thin-layer chromatography (TLC) of pyrazoles contains a large collection of Rf values for 1 1 mixtures of petroleum ether-chloroform or benzene-chloroform as eluents and alumina as stationary phase. 1,3- and 1,5-disubstituted pyrazoles can be separated and identified by TLC (Rf l,3>i y 1,5). For another publication by the same authors on the chromatographic separation of the aminopyrazoles, see (63JGU2519). A-Unsubstituted pyrazoles move with difficulty and it is necessary to add acetone or methanol to the eluent mixture. Other convenient conditions for AH pyrazoles utilize silica gel and ethyl acetate saturated with water (a pentacyanoamine ferroate ammonium disodium salt solution can be used to visualize the pyrazoles). 

The progress of the reaction may be followed by analytical thin-layer chromatography on alumina. The submitters used polygram pre-coated plastic sheets (Alox N/UV254) purchased from Macherey-Nagel, Inc. The plates were developed with 1 1 hexane-ether and stained with basic permanganate. The Rf of the product is 0.56. 

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. 

The difference between this technique and GC or HPLC is that the separation process occurs on a flat essentially two-dimensional surface. The separated components are not usually eluted from the surface but are examined in situ. Alternatively, they can be removed mechanically for further analysis. In thin-layer chromatography (TLC), the stationary phase is usually a polar solid such as silica gel or alumina which is coated onto a sheet of glass, plastic, or aluminium. Although some moisture is retained by the stationary phase, the separation process is predominantly one of surface adsorption. Thin layers are sometimes made from ion-exchange or gelpermeation materials. In these cases the sorption process would be ion-exchange or exclusion. 

N-methylcarbamate and N,N -dimethylcarbamates have been determined in soil samples by hydrolyses with sodium bicarbonate and the resulting amines reacted with 4-chloro-7-nitrobenzo-2,l,3-Oxadiazole in isobutyl methyl ketone solution to produce fluorescent derivatives [81]. These derivatives were separated by thin layer chromatography on silica gel G or alumina with tetrahydrofuran-chloroform (1 49) as solvent. The fluorescence is then measured in situ (excitation at 436 nm, emission at 528 and 537nm for the derivatives of methylamine and dimethylamine respectively). The... 

Also thin-layer chromatography is applied to the separation of both elements . Pertechnetate and molybdate can be separated on silica gel or alumina with mixtures of 1 M HCl methanol or 1 M HCl ethanol (1 5) as solvent and also on cellulose MN 300 with butanol saturated with 1 M HCl . 

Thin-layer chromatography (TLC) is often used as a faster alternative to paper chromatography. Instead of paper, a thin layer of silica gel or alumina coated onto glass, metal or plastic is used. The water held on the silica gel or alumina is the stationary phase. The mobile phase is a suitable solvent or a mixture of solvents. The solvent flows through the stationary phase and carries the components of the mixture with it. Different components in the mixture travel across the stationary phase at different rates. 

Details of the extraction methods for ficine (4) and isoficine (5) were not given. Phyllospadine (6) was isolated from the flavonoid-containing n-butanol-soluble extract from dried plant material (4). The alkaloids from Vochysia and Buchenavia were isolated by conventional procedures, utilizing acid-base extraction and subsequent column or thin-layer chromatography using silica gel or alumina (5,6). 

Thin layer chromatography (TLC) uses the same principles as GC or HPLC but is performed on a glass plate containing an adsorbent, such as silica or alumina, that attracts other molecules to its surface. A small portion of the sample to be analyzed is spotted on the plate. The plate is placed upright in a tank containing a small amount of solvent that then rises up the plate and separates the components of the sample. The separated components can be located with an ultraviolet lamp or by spraying the plate with chemicals to produce color. 

Thin layer chromatography is in principle similar to paper chromatography when used in the ascending method, i.e. the solvent creeps up the stationary phase by capillarity. The adsorbent (e.g. silica, alumina, cellulose) is spread on a rectangular glass plate (or solid inert plastic sheet). Some adsorbents (e.g. silica) are mixed with a setting material (e.g. CaSC>4) by the manufacturers which causes the film to set on drying. The adsorbent can... 

Thin-layer chromatography is now more widely used than paper chromatography. In addition to its greater resolving power, TLC is faster and plates are available with several sorbents (cellulose, alumina, silica gel). 

For a method to be used to follow the course of a chemical research, the method given in Ref 33 might be used to advantage. In this method RDX is detd in HMX in concns of 0.05 to 5% by Thin-Layer Chromatography on alumina coated plates. The RDX is recovered from the subscrate by extraction with acetonitrile and is measured by spectrophotometry at 228 millimicrons. See also Analytical Procedures under RDX in this Volume Note This Section was written in collaboration with E.F. Reese of PicnArsn)... 

The more recent applications of open-column chromatography in fat-soluble vitamin assays utilize liquid-solid (adsorption) chromatography using gravity-flow glass columns dry-packed with magnesia, alumina, or silica gel. Such columns enable separations directly comparable with those obtained by thin-layer chromatography to be carried out rapidly on a preparative scale. 

The removal of sterols, vitamin E vitamers, carotenoids, and other interfering material from the unsaponifiable fraction of food samples has been achieved using one or more of the following techniques coprecipitation of sterols with digitonin (91), precipitation of sterols from a methano-lic solution (195,209), adsorption chromatography on open columns of alumina (70,91,96), thin-layer chromatography on silica plates (209), and solid-phase extraction on silica (68,100) and reversed-phase (210) cartridges. 

Oxidation may be monitored by thin-layer chromatography (Alumina GF Uniplate, 1 1 ethyl acetate hexane). The Rf values of the N-oxide product and starting material are 0.30 and 0.79 respectively (Note 7). 

Liquid/Solid Chromatography (LSC) is adsorption chromatography. Adsorbents such as alumina and silica gel are packed in a column and the sample components are displaced by a mobile phase. Thin layer chromatography and most open column chromatography are considered liquid/solid chromatography. 

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