Benedict's reagent 184383 222301118 2008-06-28T16:25:41Z DOI bot 6652755 Citation maintenance. Added: pmid. Formatted: doi. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. '''Benedict's reagent''' (also called '''Benedict's solution''' or '''Benedict's test''') is a chemical [[reagent]] named after an American chemist, [[Stanley Rossiter Benedict]].<ref name = benedict>{{cite journal | author = Benedict, S. R. | title = A Reagent For the Detection of Reducing Sugars | journal = J. Biol. Chem. | volume = 5 | issue = | pages = 485–487 | year = 1908 | url = http://www.jbc.org/cgi/reprint/5/6/485}} </ref> Benedict's reagent is used as a test for the presence of all [[monosaccharide]]s, and generally also [[reducing sugar]]s. These include [[glucose]], [[galactose]], [[mannose]], [[lactose]] and [[maltose]]. Even more generally, Benedict's test will detect the presence of [[aldehyde]]s (except aromatic ones), and alpha-hydroxy-ketones, including those that occur in certain ketoses. Thus, although the ketose [[fructose]] is not strictly a reducing sugar, it is an alpha-hydroxy-ketone, and gives a positive test because it is converted to the aldoses [[glucose]] and [[mannose]] by the base in the reagent.<ref>[http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/D-Fehling-e.htm Fehling's Test for Reducing Sugars<!-- Bot generated title -->]</ref>. Benedict's reagent can be prepared from [[sodium carbonate]], [[sodium citrate]] and [[copper(II) sulfate]].<ref>{{cite journal | author = Robert D. Simoni, Robert L. Hill, and Martha Vaughan | title = Benedict's Solution, a Reagent for Measuring Reducing Sugars: the Clinical Chemistry of Stanley R. Benedict | journal = J. Biol. Chem. | volume = 277 | issue = 16 | pages = 10–11 | year = 2002 | url = http://www.jbc.org/cgi/content/full/277/16/e5 | doi = 10.1074/jbc.M110516200 | pmid = 11773074}}</ref> It is often used in place of [[Fehling's solution]]. Benedict's reagent contains blue copper(II) ions (Cu<sup>2+</sup>) which are reduced to copper(I) (Cu<sup>+</sup>). These are [[precipitate]]d as red [[copper(I) oxide]] which is insoluble in water. ==Chemical test== To test for the presence of monosaccharides and reducing disaccharide sugars in food, the food sample is dissolved in water, and a small amount of Benedict's reagent is added. The mixture is heated in a boiling water bath, and any precipitate formed is recorded as a positive result for the presence of reducing sugars in the food. The common disacharrides lactose and maltose are directly detected by Benedict's reagent, because each contains a glucose with a free reducing aldehyde moiety, after isomerization. [[Sucrose]] (table [[sugar]]) contains two sugars (fructose and glucose) joined with by their [[glycosidic bond]] in such a way as to prevent the glucose isomerizing to aldehyde, or the fructose to alpha-hydroxy-ketone form. Sucrose is thus a non-reducing sugar which does not react with Benedict's reagent. Sucrose indirectly produces a positive result with Benedict's reagent if heated with dilute hydrochloric acid prior to the test, although after this treatment it is no longer sucrose. The acidic conditions and heat break the [[glycosidic bond]] in sucrose through [[hydrolysis]]. The products of sucrose decomposition are glucose and fructose, both of which can be detected by Benedict's reagent, as described above. [[Starch]]es do not react or react very poorly with Benedict's reagent, due to the relatively small number of reducing sugar moieties, which occur only at the ends of carbohydrate chains. [[Inositol]] (myo-inositol) is another carbohydrate which produces a negative test. Benedict's reagent can be used to test for the presence of glucose in [[urine]]. Glucose found to be present in urine is an indication of [[diabetes mellitus]]. Once a reducing sugar is detected in urine, further tests have to be undergone in order to ascertain which sugar is present. Only glucose is indicative of diabetes. ==Quantitative reagent== '''Benedict's [[quantitative]] reagent''' is used to determine how much reducing sugar is present. This solution forms as white precipitate rather than a red one and so can be used in a [[titration]]. The titration should be repeated with 1% glucose solution instead of the sample for [[calibration]]. ==References== <references/> [[Category:Copper compounds]] [[Category:Chemical tests]] [[Category:Coordination compounds]] [[Category:Oxidizing agents]] [[de:Benedict-Reagenz]] [[es:Reacción de Benedict]] [[nl:Benedicts reagens]] [[ja:ベネジクト液]] [[pl:Próba Benedicta]] [[pt:Reagente de Benedict]] [[zh:本尼迪克试剂‎]]