Differentiation between Glucose, Galactose and Mannose by a Colour Reaction

Abstract

THREE naturally occurring aldohexoses—glucose, mannose and galactose—can readily be differentiated by the following method. Add 2 mgm. of the unknown sugar material to a solution of pyrocatechol at a concentration of 0.2 per cent in 85 per cent phosphoric acid syrup. Heat for 15 min. in a boiling water bath, shaking vigorously at the end of the first minute of heating to effect solution of the sugar. In these conditions, glucose produces a lilac colour, mannose produces a brown colour and galactose produces a red colour intermediate in quality between the colours afforded by glucose and mannose. The test is applicable equally to free and polymerized aldohexose. Amino-acids (apart from tryptophane) and gelatine do not produce colour in these conditions, and do not interfere even in large amount with this test.