Silica gel precoated plates

TLC is carried out on a 5 x 20 cm silica gel precoated plate (Merck) with a solvent system of pyridine-ethylacetate-acetic acid-water (75 25 15 30), tert-butanol-acetic acid-water (2 1 1) or n-butanol-acetic acid-water (60 15 25) (11). 

TLC is used for qualitative analysis its reproducibility is relatively poor. For the analysis of dyes by TLC, extracts are spotted on areas as small as possible on the silica gel precoated plate and developed by a suitable developing solvent. Selection of developing systems depends on the chemical properties of... 

Zlatanov, L., Gonnet, C., and Marichy, M. (1986). Demixing effects in thin layer chromatography with NHj-modified silica gel precoated plates. Chromatographia21 331-... 

Retention (hRfi, hRf2) Resolution (u, Rs) Data of DL-Dansyl-Amino Acids (Dns-AA) on Silanized Silica Gel Precoated Plates (RP-18 Merck) Impregnated with the Copper (II) Complex of Various Chiral Selectors... 

An interesting application of this technique concerned the use of silica gel precoated plates impregnated with unusual chiral selectors, such as L-lactic acid... 

Estriol Dip the concentrating zone of a precoated H PTLC silica gel 60 plate in a saturated ethanolic solution of Fast Dark Blue R salt, allow the solvent to evaporate, apply the sample solution and dip once [10, 59]... 

Merck precoated silica gel F254 plates, layer thickness 0.25 mm., were used. Developing with 10 1 (vjv) benzene-acetone and visualizing with ultraviolet light, the product appears at Rf 0.58 0.67. Normally the product is found in the lower third of the column, and occasionally some is found in the last fractions of eluent collected during development. However, since the exact position of this material on the column depends critically on the way in which the column is packed, a thorough check of all fractions is advisable. 

The literature reports [a]n +23.2° (c = l, aqueous 5N hydrochloric acid). The product was analyzed by the submitters. Analysis caleulated for C5H11NO2S C, 40.25 H, 7.43 N, 9.39 S, 21.49. Found C, 40.14 H, 7.42 N, 9.50 S, 21.52. The product was homogeneous according to thin-layer chromatograms on precoated silica gel G plates purchased from Analtech, Inc., Newark, Delaware, and developed with the following two solvent systems (solvents, volume ratios of solvents in the same order) 1-butanol-acetic acid-ethyl acetate-water, 1 1 1 1, Rf 0.49 1-butanol-acetic acid-pyridine-water, 15 3 10 12, R/0.51. 

Silica-gel-precoated preparative TLC plates impregnated with AgNOj are widely applied in this technique [60,90]. To impregnate a silica-precoated plate with silver nitrate, the plate is dipped for 3 min in a 1% AgNOj solution in a methanol-water mixture (4 1, v v). The plate is then dried, first in air with exclusion of light, and next, it is activated at 80°C in a drying oven. If impregnated plates are not used immediately, they should be stored wrapped in black plastic film in a desiccator [90-92]. 

Thin layer chromatography. Thin layer chromatography (TLC) was carried out on precoated Silica gel 60 plates (Merck) with the solvent system benzene-acetone-methanol-6N acetic acid (150 80 19 1). Toxins were detected by heating the plates after spraying 50% sulfuric acid. 

The progress of the reaction can be monitored by TLC by working up a sample of the reaction mixture filter through Celite, cool to 0°C, and acidify to pH 1 with 10% aqueous HCI. The solid that precipitates is isolated by filtration and dissolved in dimethylformamide (DMF) for TLC analysis on Merck precoated-silica gel 60 plates with methyl ethyl ketone-methanol-water (4 1 1) as eluent, developed by dipping in 5% sulfuric acid-ethanol and heated to 450°C (e.g., with a Bunsen burner). Rf values are 0.25 for fl-cyclodextrin, 0.5 for monotosylate and 0.65 for a second product, probably ditosylate. 

Another spray used to detect the vinyl ether phosphoglycerides on thin layer chromatograms is one containing 2,4-dinitrophenylhydrazine in 2N HC1 or 2 N H2S04. However, when using this spray, it is first necessary to run the sample, spotted on a precoated silica gel G plate, 250 pm, in chloroform-methanol-water (65 35 7, v/v). At the end of the development, the plate is allowed to air dry and then is exposed to HC1 fumes (usually the plate is suspended above a dish containing 12 N (concentrated) HC1 for several minutes). It is then sprayed with the dinitrophenylhydrazine reagent. If an aldehyde is present, a yellow spot will appear within a few minutes at most. 

In the determination of polycychc aromatic hydrocarbons (PAHs), the separation is performed either on caffeine-impregnated HPTLC silica gel 60 plates, on HPTLC-RP-18 plates with a concentration zone or on precoated HPTLC silica gel 60 plates with a concentration zone (Merck Item Nos. 1.15086,1.15037,1.13728). Subsequent dipping in paraffin/n-hexane (1 4) gives not only stabilization of the PAHs on the plate but also an increase in the fluorescence intensity by a factor of 4-5 [83a]. 

Goldenseal and related alkaloids were qualitatively identified and quantitatively determined using TLC/DESI analysis. The TLC separations were performed using aluminum sheets precoated with silica gel 60 F254, or using glass-backed silica gel 60 plates. After the application of analytes, the plates were developed in ascending... 

ToIuene ethyi acetate (7 3) or chloroform methanol (8 2) Precoated silica gel GF plates 292 nm a [54]... 

Several aminoglycoside antibiotics were identified by TLC with different solvent systems and visualizing with two reagents (29). Precoated silica gel 60 plates (Merck) and laboratory-made plates with silica gel H + 1% Carbopol 936 were used. A 10-pl volume of the aminoglycoside and 20 ll of the commercial gentamicin were applied and developed to a height of 15 cm in the following solvents ... 

Brain and extraneural gangliosides Densitometry Complex sample preparation TLC on precoated EM silica gel 60 plates chloroform-methanol-0.25% CaCL (60 35 8) solvent system detection with the resorcinol reagent scanned at 580 nm in the reflectance mode separation of 4-8 individual gangliosides 105... 

Impregnation has also been carried out in the following manner. Precoated silica gel TLC plates, without fluorescent indicator, were dipped into a large dish. 

Fig. 42 Chromatogram of polycyclic aromatic hydrocarbons on caffeine-impregnated precoated silica gel 60 HPTLC plates with concentrating zone (Merck). The following can be recognized in increasing Rf value. — 1. benzo(ghi)perylene, 2. indeno(l,2,3-cd)pyrene, 3 benzo(a)pyrene, 4. benzo(b)fluoranthene, 5. benzo(k)fluoranthene, 6. fluoranthene.

The submitters also tried to purify the crude product by distillation (130-145° at 0.005 mm.), but under these conditions decomposition took place. It is possible to substitute thick-layer chromatography for the dry column. Using Merck silica gel F254 precoated plates, layer thickness 2 mm., and developing with 10 1 (vjv) benzene-acetone, the submitters report a 73% yield of pure product. 

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