Orcinol, quantitative determination

On the basis of characteristic color-reactions for (acylated) neuraminic acids (for example, Bial s orcinol reaction140,159 and the thio-barbituric acid method181), quantitative methods for the determination of gangliosides have been developed (for example, on thin-layer plates157,161,184,182). 

Derenbach (1970) made a distinction between soluble and combined RNA of planktonic material from the different behaviour of these compounds after different extraction procedures. He and others (see Derenbach, 1970 for references), employed the orcinol/hydrochloric acid reagent according to Ceriotti (1955). Since a variety of other sugars may interfere (see section 3.1 orcinol/sulphuric acid has also been used as a reagent for total carbohydrate determinations) correction factors or preferably chromatographic separations of the extracts are required for quantitative results. 

General color reactions of this type include the Molisch test with a-naphtfiol and concentrated sulfuric acid and the anthrone reaction with anthrone and sulfuric acid. The latter is used for quantitive colorimetric determinations. Reaction conditions can be chosen so that only ketoses react (HCl - - resorcinol, Seliwanoff s test) or only pentoses (HCl -b orcinol. Rial s test). These reactions help to distinguish the various sugars. 

---