Thin layer chromatography coatings

Thin Layer Chromatography. Coat 8- x 8-inch glass plates with a 0.25-mm. layer of aluminum oxide G, and air-dry overnight. Activate in an oven at 155°C. for 2.5 hours, and store over Drierite until used. 

Chemical stabiUty studies are monitored by siUca gel thin-layer chromatography (dc) or by high performance Hquid chromatography (hplc) using a reverse-phase C g coated column (24). Hplc peaks or dc spots are visualized by thek uv absorption at 245 nm the tic spots can also be detected by ceric sulfate or phosphomolybdic acid staining. 

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. 

Commercially available pre-coated plates with a variety of adsorbents are generally very good for quantitative work because they are of a standard quality. Plates of a standardised silica gel 60 (as medium porosity silica gel with a mean porosity of 6mm) released by Merck have a specific surface of 500 m /g and a specific pore volume of 0.75 mL/g. They are so efficient that they have been called high performance thin layer chromatography (HPTLC) plates (Ropphahn and Halpap J Chromatogr 112 81 1975). In another variant of thin layer chromatography the... 

The moist cells were suspended in 750 parts of volume of ethanol and extracted by warming at 60°C for 1 hour. A total of 3 extractions were carried out in a similar manner and the extracts were pooled, diluted with water and further extracted three times with 1,000 parts of volume portions of n-hexane. The n-hexane layer was concentrated to dryness under reduced pressure to recover 4.12 parts of a yellow oil. This oily residue was dissolved in 6 parts by volume of benzene and passed through a column (500 parts by volume capacity) packed with Floridil (100 to 200 meshes). Elution was carried out using benzene and the eluate was collected in 10 parts by volume fractions. Each fraction was analyzed by thin-layer chromatography and color reaction and the fractions rich in ubiquinone-10 were pooled and concentrated under reduced pressure. By this procedure was obtained 0.562 part of a yellow oil. This product was dissolved in 5 parts by volume of chloroform, coated onto a thin layer plate of silica gel GF254 (silica gel with calcium sulfate) and developed with benzene. The fractions corresponding to ubiquinone-10 were extracted, whereby 0.054 part of a yellow oil was obtained. This oil was dissolved in 10 parts by volume of ethanol and allowed to cool, whereupon 0.029 part of yellow crystals of ubiquinone-10 were obtained, its melting point 4B°to 50°C. 

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. 

Analysis by thin layer chromatography (TLC) indicates product formation and a small amount of starting material. TLC was performed on Merck Silica gel 60 F-254 coated on aluminum sheets. Product 3 has Rf = 0.44 (elution with 70 30 petroleum ether-ethyl acetate visualization with iodine vapor). 

Tswett s initial column liquid chromatography method was developed, tested, and applied in two parallel modes, liquid-solid adsorption and liquid-liquid partition. Adsorption ehromatography, based on a purely physical principle of adsorption, eonsiderably outperformed its partition counterpart with mechanically coated stationary phases to become the most important liquid chromatographic method. This remains true today in thin-layer chromatography (TLC), for which silica gel is by far the major stationary phase. In column chromatography, however, reversed-phase liquid ehromatography using chemically bonded stationary phases is the most popular method. 

Test 3. According to the general method (2.2.27), examine by thin-layer chromatography using a suitable octadecylsilyl silica gel as the coating substance. 

Examine the sample by thin-layer chromatography, using silica gel G R as the coating substance. Dissolve 10 mg of the substance to be examined in 4 mL of water R as a test solution, and dissolve 10 mg of penicillamine reference substance in 4 mL of water R as a reference solution. Apply 2 pL of each solution separately to the plate. Develop over a path of 10 cm using a mixture of 18 volumes of glacial acetic acid R, 18 volumes of water R, and 72 volumes of butanol R. Dry the plate at 100-105 °C for 5-10 min, and expose to iodine vapor for 5-10 min. The principal spot in the chromatogram obtained with the test solution is similar in position, color, and size to the principal spot in the chromatogram obtained with the reference. 

Test 3 Examine by thin-layer chromatography, as specified in the general procedure (2.2.27), using as the coating substance a suitable silica gel with a fluorescent indicator having an optimal intensity at 254 nm. 

Examine by thin-layer chromatography (TLC) using a suitable TLC silica gel as the coating substance on the TLC plate. The method requires preparation of the following solutions ... 

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. 

Most of the reactions described in the following chapters were monitored by Thin Layer Chromatography (TLC) using plastic TLC plates coated with a thin layer of Merck 60 F254 silica gel. The products were detected by using an ultraviolet lamp or the TLC plates were treated with p-anisaldehyde reagent, prepared as explained below, and then heated to 120 °C to stain the spots. After visualization and measurement, the Rf values were recorded. 

Thin layer chromatography was carried out on 20x20cm glass plates coated 0.25mm thick with a suitable support and dried overnight. Silica gel G, silica gel H and cellulose were examined as the solid phases for chromatography of methanearsonate, arsenite and arsenate. Several sprays for the visualization of the arsenicals on plates were tested. Three of the more successful reagents and the colour produced with final product are shown in Table 13.2. 

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. 

TLC. Aliquots of samples and standards were run on silica-coated thin layer chromatography (TLC) plates in either n-butanol/acetic acid/water (4 1 1 by vol. (BUOH/HAC/H2O)) or n-propanol/concentrated ammo-nia/water (8 1 11, pre-equilibration). These eluents were previously described (Keller et ah, 1984) for the two-dimensional TLC-separation of elastin cross-links. 

Thin Layer Chromatography Procedures. Silica gel G (Suppelco, Redi-coat, 5 X 20 cm X 0.25 mm) plates were activated by heating in an oven for 1 hour at 110°C. Toxic products were spotted onto duplicate plates at concentrations corresponding to their previously determined LD99 levels. The plates were developed to 14 cm with chloroform, methanol and (6N) ammonium hydroxide (90 9.5 0.5) or chloroform, methanol, and water (60 35 8). Plates were developed and visualized by spraying with 50% aqueous sulfuric acid and charring. Undeveloped plates were scraped, the silica gel fines removed and the extracts concentrated to a residue under a nitrogen gas stream. 

The ultraviolet reflectance absorbance spectrum of a benzoic acid spot on a thin-layer chromatography place was recorded on a Shimadzu CS-930 TLC scanner, and is shown in Figure 5. The spectrum was obtained on a silica-gel F254 pre-coated TLC-plate (E. Merck) after elution with 7 2 2 acetone/ammonia 25 %/isopropanol. The absorbance maximum for this system was determined to be 225 nm. 

As discussed in Chapter 3, thin-layer chromatography utilizes a thin coating of silica gel on a glass or plastic plate to separate components of a mixture. The mixture of chemical substances to be analyzed is applied near one edge... 

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