Carbohydrates phenol-sulfuric acid reaction

Method 2 (phenol-sulfuric acid reaction). The reaction of carbohydrates with phenol in the presence of sulfuric acid produces a UV-absorbing chromophore which is sufficiently sensitive to be used as a means of detecting less than 1-pg amounts of carbohydrates... 

Post-column derivatization of carbohydrates has been described for liquid chromatography and UV detection by heat treatment [46], acid treatment [47] and reaction with phenol-sulfuric acid [48,49]. These methods have been applied to the analysis of sugars in body fluids and in wood products. The procedures are only suitable for low-speed liquid chromatography. 

Anthrone (9,10-dihydro-9-oxo-anthracene) reacts with most carbohydrates in concentrated sulfuric acid to produce a characteristic blue color, with an absorption maximum at 625 nm. This reaction has been automated and was once widely used in analysis of dextran fractions emerging from size exclusion columns. However, as in the case of the phenol-sulfuric acid method, the presence of concentrated acid necessitates special precautions (such as the inclusion of a pulse suppressor) and for this reason, and also because of the instability of the reagent, the method is seldom used today except in manual analysis. 

The sulfate group can be transferred easily, i.e. in exergonic reactions, to phenols and alcohols. These sulfuric esters have long been known as detoxication and excretion forms of various foreign substances and metabolic products. They include phenol sulfuric acid, indoxyl sulfuric acid (indican), and estrone sulfuric acid. The sulfuric esters of carbohydrates arise presumably in a similar manner (Chapt. XVII-7). 

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