Benedict's reagent
Benedict's reagent, also called Benedict's solution, is a reagent used to test for reducing sugars, named after American chemist Stanley Rossiter Benedict.[1][2] Similar to Fehling's reagent, it is an alkaline solution of copper(II), but it is stabilized by citrate ions rather than tartrate ions and is less corrosive and more stable to storage.[2]
Contents
Reagent
The reagent is prepared by dissolving 100 g of anhydrous sodium carbonate, 173 g of trisodium citrate dihydrate and 17.3 g of copper(II) sulfate pentahydrate in water, and diluting to 1 litre.[1] The final solution is 71.3 mmol dm−3 in copper(II) and 588 mmol dm−3 in total citrate (an eightfold excess over copper), with a pH of about 12. The copper(II) is believed to be present as a 1:1 citrate complex, [Cu(C6H5O7)(OH)(H2O)n]2− (n = 0, 1).[3] The prepared solution can be stored for at least a year under normal laboratory conditions, unlike Fehling's reagent or Tollen's reagent, which must be prepared freshly before each use.[1]
Test
A few drops of the solution to be tested are added to about 5 cm3 of the reagent in a test tube. The mixture is heated to 100 °C and kept at that temperature for one or two minutes, then allowed to cool. The presence of an abundant precipitate, which can be red, yellow or green, indicates the presence of reducing sugar. The test is sensitive to 1 g dm−3 (5 mmol dm−3) glucose.[1]
Benedict's reagent was widely used in clinical chemistry to test for glucose in urine, a clear sign of diabetes: it has now been superseded by enzymatic methods, particularly those based on glucose oxidase.[2]
References
- ↑ 1.0 1.1 1.2 1.3 Benedict, Stanley R. A Reagent For the Detection of Reducing Sugars. J. Biol. Chem. 1908, 5 (6), 485–87, <http://www.jbc.org/content/5/5/485.full.pdf>.
- ↑ 2.0 2.1 2.2 Simoni, Robert D.; Hill, Robert L.; Vaughan, Martha Benedict's Solution, a Reagent for Measuring Reducing Sugars: the Clinical Chemistry of Stanley R. Benedict. J. Biol. Chem. 2002, 277 (16), e5, <http://www.jbc.org/content/277/16/e5.full.pdf>.
- ↑ Field, Terrence B.; McCourt, Janet L. Composition and Stability of Iron and Copper Citrate Complexes in Aqueous Solution. Can. J. Chem. 1974, 52, 3119–24, <http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?issn=1480-3291&volume=52&issue=17&startPage=3119>.
External links
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See also the corresponding article on Wikipedia. |
- Benedict's Test for Reducing Sugars
- Colorimetric Identification of Unknown Sugars
- Reagents for biochemistry
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