Coating TLC Plates

Practical Tips for coating TLC plates with blood-gelatin reagent  

The beer money is a tip for the slaughterhouse worker whose job will have to be interrupted for your benefit. He will fill the glass jar with fresh blood, close it. 

After the chromatography, the plate, from which the solvent has been removed, is surroimded on all four sides by a 3-cm wide adhesive textile band so that a border ca. 1 cm high is formed which will prevent the blood-gelatin reagent applied later from miming off (Fig. 88a,b). Using a spirit level, the plate is placed on a horizontal substrate (Fig. 88a). 

If available, a cooling block forms a particularly good base for the plate which is to be coated, as this enables the reaction time to be considerably shortened. 

Example of a derivatization by coating saponin-containing drugs 

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Procedure Apply separately to the coated TLC plate 1 p/ of each of three solutions (1), (2) and (3). Develop the plate in the above mobile-phase such that the solvent front is allowed to ascend only 10 cm above the line of application. After removal of the plate, dry it at 100 °C to 105 °C for 15 minutes, allow to cool and spray with dilute potassium iodobismuthate solution until spots appear. 

This type of test could be carried out equally well with commercially produced ODS plates. Silica gel plates can be simply modified with reaction with organosilane reagents, the availability of a wide range of reactive organosilanes means that there is potential for producing a wide range of coated TLC plates for specific purposes. 

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. 

Analytical thin layer chromatography (TLC) was conducted on pre-coated TLC plates, silica gel 60 F254, layer thickness 0.25 mm, manufactured by E. Merck and Co., Darmstadt, Germany. Silica Gel for flash column chromatography was obtained from Silicycle Chemical Division Silica Gel, 60 (particle size 0.040 - 0.063 mm) 230-240 mesh ASTM. All columns were prepared, loaded, and fractions collected according to the specification of Still.37 Ethyl acetate used for chromatography was dried over 4 A molecular sieves for at least 24 hours prior to use. Hexanes are the mixed hydrocarbon fraction (bp 60-70 °C), principally n-hexanes, which was purified as follows the commercial solvent was stirred concentrated sulfuric acid for at least 24 hours, decanted, stirred over anhydrous sodium carbonate for 6 hours, decanted, then distilled. 

This book is the result of cooperation between four colleagues, who have been working in the field of thin-layer chromatography for many years and, in particular, took an active part in the development from hand-coated TLC plates to... 

The semioxamazone is prepared by refluxing a mixture of 0.04 mole of 3, 0.04 mole of aldehyde 1, and 0.5 g of p-toluenesulfonic acid in 400 mL of anhydrous benzene until no starting aldehyde can be detected by TLC (about 10 minutes for 4b). Pre-coated TLC plates (silica gel 60 F-254, eluent diethyl ether/ hexane 90/10). The benzene is removed on a rotary evaporator and a red-orange, solid crude product is obtained, which is a —50 50 mixture of the diastereomers. 

Silica gel specific surface area SOOemVg pore volume 0.75 cm7g pore diameter 60 A, The TLC is performed on siliacagel 60 l, 3, glas-coated TLC-plates from Merck (Germany), a company with world wide representation. 

There are a few techniques related to normal phase chromatography that are worth mentioning. Silica can be coated with the salts of heavy metals. This results in unique selectivities for analytes that form complexes with the metal ions. An example of this is argentation chromatography (20). The silica is coated with silver nitrate, which gives it a spedal sel ivity for compounds with al atic double bonds. The technique has acquired a broad range of applications. However, while Ag -coated TLC plates are commercially available, HPLC columns have to be prepared by the user. Other metal salts can be used in a similar manner for different applications. 

In some cases, an online combination of cellulose-coated TLC plates and MALDl-MS produces higher quality MS spectra with no or little background compared to an offline approach. In the latter case, pure sample test solution and matrix are crystallized on a conventional metal MALDI plate and several interfering signals are observed in the MS, which originate from matrix ions and cluster ions, respectively. This concept was readily presented in the analysis of triterpenoids [10]. 

The first online TLC-MS attempt in the field of triterpenoids was done only in 2005 in the study of the photo-oxidation of natural di- and triterpenoid resins used as paint varnishes [10], The resinous samples were applied onto a cellulose-coated TLC plate, which afterward was subjected to direct MALDI-TOF-MS analysis without any development. The plates were only sprayed with a saturated ethanol solution of 2,5-dihydroxybenzoic acid as matrix to assist the ionization of compounds. Triterpenoids were observed as protonated molecules or as sodium clusters. Dammaradienone, dammaradienol, nor-a-amyrone, and dammarenolic, oleanonic, and ursonic acid were detected in dammar resin moronic acid, masticadienonic acid, and 3-0-acetyl-3-epi(iso)masticadienonic acid were found in mastic resin and diterpenoid abietane and pimarane acids were present in colophony. The induced aging process produced oxidized triterpenoids, which were observed in the MS spectra... 

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