Barfoed's Test for Monosaccharides

This reaction will detect reducing monosaccharides in the presence of disaccharides. This reagent uses copper ions to detect reducing sugars in an acidic solution. Barfoed's reagent is copper acetate in dilute acetic acid (pH 4.6). Look for the same color changes as in Benedict's test.

Method

Add 1 ml of the solution to be tested to 3 ml of freshly prepared Barfoed's reagent. Place test tubes into a boiling water bath and heat for 3 minutes. Remove the tubes from the bath and allow to cool. Formation of a green, red, or yellow precipitate is a positive test for reducing monosaccharides. Do not heat the tubes longer than 3 minutes, as a positive test can be obtained with disaccharides if they are heated long enough.