THE USE OF THE MOLISCH (a-NAPHTHOL) REACTIONS IN THE STUDY OF SUGARS IN BIOLOGICAL FLUIDS BY

The cy-naphthol (Molisch) reaction for sugars has been neglected as a possible basis for a quantitative method. As a ring test, the only form in which it is ever described, it is very crude. The violet colors produced at the surface of contact of concentrated sulfuric acid and a sugar solution containing cr-naphthol are often obscured by charring. The lack of control of the concentration of sugar tends to give results which appear qualitatively the same for all carbohydrates. The present paper describes a modification of the test and the results which it gives with various sugars and biological fluids as observed with a spectrophotometer. It will deal only with the qualitative nature of the reaction. The application of the Molisch reaction to a method for estimating very small quantities of carbohydrates will be described in future communications. The chemical basis of the a-naphthol test is the production of furfural derivatives on heating carbohydrates with strong acids and the condensation of these furfuraldehydes with cr-naphthol to give colored compounds. In the Molisch ring test concentrated sulfuric acid is used both to produce the furfural derivatives and as the condensing agent. For ordinary laboratory purposes the following procedure will give a delicate and satisfactory test. The color resulting will be evenly distributed throughout the test mixture and there will be no interference by charring.