Barfoed's test is a chemical test used for detecting the presence of monosaccharides. It is based on the reduction of copper(II) acetate to copper(I) oxide (Cu2O), which forms a brick-red precipitate.
- RCHO + 2Cu2+ + 2H2O → RCOOH + Cu2O↓ + 4H+
(Disaccharides may also react, but the reaction is much slower.) 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.
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.
2-3 drops of Barfoed's reagent is added to 1 mL of given sample in a test tube and boiled for 30 seconds and then allowed to cool. If a red precipitate occurs, a monosaccharide is present.
- C. Barfoed (1873). "Über die Nachweisung des Traubenzuckers neben Dextrin und verwandten Körpern". Fresenius' Zeitschrift für Analytische Chemie. 12 (1): 27. doi:10.1007/BF01462957.
- Biochemistry Department. "Colorimetric Identification of Unknown Sugars". Biochemistry Laboratory 353. Smith College. Archived from the original on 2006-07-16.
- William H. Welker (1915). "A Disturbing Factor in Barfoed's Test". J. Am. Chem. Soc. 37 (9): 2227–2230. doi:10.1021/ja02174a036.
- Bowen, Graham and Williams (1957). A Students' Handbook of Organic Qualitative Analysis. University of London Press. p. 73.