Barfoed's test
{{Short description|Chemical test for monosaccharides}}
{{ infobox chemical analysis
| name = Barfoed's test
| image = File:Positive result in Barfoed's test.jpg
| caption = Positive result in Barfoed's test
| acronym =
| classification = Colorimetric method
| analytes = Monosaccharides
| manufacturers =
| related =
| hyphenated =
}}
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.{{cite journal
| title = Über die Nachweisung des Traubenzuckers neben Dextrin und verwandten Körpern
| author = C. Barfoed
| journal = Fresenius' Zeitschrift für Analytische Chemie
| volume = 12
| issue = 1
| pages = 27
| year = 1873
| url = https://zenodo.org/record/1594255
| doi = 10.1007/BF01462957
| s2cid = 95749674
}}{{cite web|work=Biochemistry Laboratory 353 |title=Colorimetric Identification of Unknown Sugars |publisher=Smith College |author=Biochemistry Department |url=http://www.science.smith.edu/departments/Biochem/Biochem_353/CARBO.html |url-status=dead |archiveurl=https://web.archive.org/web/20060716052807/http://www.science.smith.edu/departments/Biochem/Biochem_353/CARBO.html |archivedate=2006-07-16 }}
::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,{{cite journal | author = William H. Welker | journal = J. Am. Chem. Soc. | year = 1915 | doi = 10.1021/ja02174a036 | pages = 2227–2230 | title = A Disturbing Factor in Barfoed's Test | volume = 37 | issue = 9 | url = https://zenodo.org/record/1428983 }} may interfere.
Its author is the Danish chemist Christen Thomsen Barfoed and it is primarily used in botany.{{Citation needed|date=April 2009}}
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.{{cite web |title=Barfoed Reagent Safety Data Sheet |url=http://browardcentralscience.org/sds/barfoeds%20reagent.pdf |website=Broward Central Science |publisher=Carolina Biological Supply Company |accessdate=10 September 2020 |archive-date=14 February 2020 |archive-url=https://web.archive.org/web/20200214175228/http://browardcentralscience.org/sds/barfoeds%20reagent.pdf |url-status=dead }} The reagent does not keep well and it is therefore advisable to make it up when it is actually required.{{Cite book | author = Bowen, Graham and Williams | title = A Students' Handbook of Organic Qualitative Analysis | publisher = University of London Press | date = 1957 | page = 73}}
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
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{{Organic reactions}}
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