Bial s orcinol reagent

Colominic acid is an acidic aminopolysaccharide elaborated in the culture medium of Escherichia coU K235 from which it can be isolated by alternate dialysis and lyophilization followed by fractional precipitation with aqueous ethanol and ammonium sulphate. Pure preparations ([a] —50.5° 2° in water) showed a single peak (mobility —ii.i-io- cm /volt.sec) when subjected to electrophoretic analysis in o.i M borate buffer pH 9.2. It was degraded by acid with formation of humin and when heated in o.i iV alkali gave a product with A 260 m/z in the ultraviolet. It reacted both with Ehrlich s reagent 53om )and Bial s orcinol reagent 540 m ). 

Soon afterward, Blix (1938) demonstrated that this carbohydrate from submaxillary mucin generated a purple chromophore with Bial s orcinol reagent that had the same absorption maximum as that reported... 

Bial s reagent (for pentoses) dissolve 1 g of orcinol in 500 mL of 30% HCl to which 30 drops of a 10% ferric chloride solution have been added. 

By careful choice of both the reaction conditions and the phenolic compound used, it may be possible to produce a colour that is characteristic of a particular carbohydrate or related group, so giving some degree of specificity to the method. Thus, Seliwanoff s test uses hydrochloric acid and either resorcinol or 3-indolylacetic acid to measure fructose with minimal interference from glucose. The colour produced by pentoses with orcinol (Bial s reagent) or p-bromoaniline is sufficiently different from that produced by hexoses to permit their quantitation in the presence of hexoses. However, none of the methods based on the formation of furfural or its derivatives can be considered to be entirely specific. 

Measuring the rate of disappearance of ribose-5-phosphate in the first reaction with orcinol reagent (i.e. Bial s test, q.v.). 

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