Charring reagents

The combination of copper salts and snlfnric acid is another widely used charring reagent. For preparation, 10 ml of concentrated H2SO4 has to be mixed carefully with 90 ml of acetic anhydride. Three grams of copper-II-acetate is dissolved in 100 ml of 8% phosphoric acid. After plate dipping or plate spraying, 15 min of heating at 125°C is recommended [17]. 

Highly nonpolar compounds such as fatty acids, glycerides, alkanes, and some lower terpenoids require simple nonpolar solvent systems (e.g., cyclohexane, hexane, pentane, diethyl ether.hexane mixtures) and may be difficult to detect by UV (i.e., no chromophore) or by spray detection (use charring reagents, e.g., vanillin-sulfuric acid). 

Charring reagents have been incorporated by dipping layers to avoid spraying of corrosive chemicals. For example, silica plates have been impregnated with 4% sulfuric acid in methanol [53] or ammonium bisulfate [54]. 

Spraying of acid-charring reagents must be carried out in a hood using extreme caution. A less hazardous charring spray consists of 10-20% aqueous ammonium sulfate. Heating the sprayed chromatogram decomposes the salt to produce sulfuric acid in situ. Commercial plates are available with 10% ammonium sulfate incorporated into silica gel G or H (Analtech). 

Sulphuric acid (charring reagent) alicyclic amines Alkaloids, amines... 

The high carbon content of RP layers hinders some common detection methods. Most charring reagents and those that do not adequately wet the layer cannot be used. Reagents that have been successfully employed on C-18 layers include iodine, 10% phosphomolybdic acid in ethanol with... 

---