Barfoed's test is used for detecting the presence of monosaccharides.
It is based on the reduction of copper(II) (as acetate) to copper(I) oxide (Cu2O), which forms a brick-red precipitate. (Disaccharides may also react, but the reaction is much slower.)
Composition:
Barfoed's reagent consists of a 0.33 molar solution of neutral copper acetate in 1% acetic acid solution. The reagent does not keep well and it is therefore advisable to make it up when it is actually required.
The aldehyde group of the monosaccharide which normally forms a cyclic hemiacetal is oxidized to the carboxylate. A number of other substances, including sodium chloride may interfere.
The test is similar to the reaction of Fehling's solution to aldehydes or Benedict's test.
There is no difference for a solution to be tested by Benedict`s or by Barfoed`s test, as both detect the presence of reducing sugars. Barfoed`s test is the least known of these three.