Materials for TLC

Cover 0.5 g of cholesterol with 5 mL of acetic acid in a small Erlenmeyer flask, swirl, and note that the initially thin slurry soon sets to a stiff paste of the molecular compound C27H45OH CH3CO2H. Add 1 mL of acetic anhydride and heat the mixture on the steam bath for any convenient period of time from 15 min to 1 h record the actual heating period. While the reaction takes place, prepare the chromatographic column. Cool, add 20 mL of water, and extract with two 25-mL portions of ether. Wash the combined ethereal extracts twice with 15-mL portions of water and once with 25 mL of 10% sodium hydroxide, dry by shaking the ether extracts with 25 mL of saturated sodium chloride solution, then dry the ether over anhydrous sodium sulfate for 10 min in an Erlenmeyer flask, filter, and evaporate the ether. Save a few crystals of this material for TLC (thin-layer chromatography) analysis. Dissolve the residue in 3-4 mL of ether, transfer the solution with a capillary dropping tube onto a column of 12.5 g of silica gel, and rinse the flask with another small portion of ether. ... 

Free amino acids and peptides are markedly hydrophilic compounds, only slightly soluble in non-aqueous solvents. This must be borne in mind when sampling and preparing materials for TLC as well as when choosing the solvent. Some data on solubilities of a few amino acids in various solvents which illustrate this are ... 

The term thin-layer chromatography was coined by Egon Stahl in Germany in the late 1950s. Stahl s greatest contribution to the field was the standardization of materials, procedures, and nomenclature and the description of selective solvent systems for the resolution of many important compound classes. His first TLC laboratory manual (Stahl, 1962) popularized TLC, and he elicited the aid of various chemical manufacturers in offering standard materials for TLC. Stahl (1979, 1983) has provided an introspective view of his contributions to the field over a period of 25 years. 

Various hydrated aluminum hydroxides serve as starting material for TLC alumina. By a series of nonuniform thermal dehydration processes, a variety of aluminas are obtained, and the ones most suitable for TLC are the crystalline modifications of x-ALOs and y-ALO (Rossler, 1969 Snyder, 1975). The physicochemical properties or the exact nature of adsorption sites of alumina are not well understood. Snyder (1975) has suggested that exposed A1 atoms, strained Al-O bonds, and perhaps other cationic sites serve as adsorption sites, whereas, unlike silica, surface hydroxyl groups are probably not important. Acids are probably retained by interaction with basic sites such as surface oxide ions. Gasparic and Churacek (1978) report that every A1 atom is surrounded by six atoms of... 

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