Barfoed's test

Barfoed's test

Positive result in Barfoed's test
Classification	Colorimetric method
Analytes	Monosaccharides

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.[1][2]

RCHO + 2Cu^2+ + 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,[3] may interfere.

Its author is the Danish chemist Christen Thomsen Barfoed[1] and it is primarily used in botany.^[citation needed]

The test is similar to the reaction of Fehling's solution to aldehydes.

Composition

Barfoed's reagent consists of a 0.33 molar solution of copper (II) acetate in 1% acetic acid solution.[4] The reagent does not keep well and it is therefore advisable to make it up when it is actually required.[5]

Procedure

1 drops of Barfoed's reagent is added to 2 mL of given sample in a test tube and boiled for 3 minutes and then allowed to cool. If a red precipitate occurs, a monosaccharide is present.

References

1. 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. S2CID 95749674.
2. Biochemistry Department. "Colorimetric Identification of Unknown Sugars". Biochemistry Laboratory 353. Smith College. Archived from the original on 2006-07-16.
3. William H. Welker (1915). "A Disturbing Factor in Barfoed's Test". J. Am. Chem. Soc. 37 (9): 2227–2230. doi:10.1021/ja02174a036.
4. "Barfoed Reagent Safety Data Sheet" (PDF). Broward Central Science. Carolina Biological Supply Company. Archived from the original (PDF) on 14 February 2020. Retrieved 10 September 2020.
5. Bowen, Graham and Williams (1957). A Students' Handbook of Organic Qualitative Analysis. University of London Press. p. 73.