Fehling's reagent
Fehling's reagent, also called Fehling's solution, is a reagent used to test for reducing sugars, named after German chemist Hermann von Fehling.[1] It is an alkaline solution of copper(II) stabilized by tartrate ions.
Contents
Reagent
The reagent is prepared immediately before use by mixing equal volumes of two solutions:
- Solution A
- 70 g of copper(II) sulfate pentahydrate dissolved in water and diluted to one litre
- Solution B
- 350 g of potassium sodium tartrate tetrahydrate ("Rochelle salt") and 100 g of sodium hydroxide dissolved in water and diluted to one litre
The final reagent is 140 mmol dm−3 in copper(II) and 620 mmol dm−3 in total tartrate (a fourfold excess over copper), with a pH of about 14. The copper(II) is present as a variety of tartrate complexes, [Cu(C4H4O6)n](2n−2)− (n = 2–6),[2] which prevents the precipitation of copper(II) hydroxide or sparingly soluble copper(II) tartrate.[3]
The mixed reagent cannot be stored, as the tartrate ions are degraded in the strongly alkaline conditions and will reduce the copper(II) to a precipitate of copper(I) oxide.[4]
Test
Fehling's reagent was used to test for glucose in urine, a clear sign of diabetes, until it was superseded by Benedict's reagent and then by enzymatic methods, particularly those based on glucose oxidase.[5]
References
- ↑ Fehling, H. Die quantitative Bestimmung von Zucker und Stärkmehl mittelst Kupfervitriol. Justus Liebigs Ann. Chem. 1849, 72 (1), 106–13. DOI: 10.1002/jlac.18490720112.
- ↑ Jespersen, Neil D. Novel Copper-Tartrate Coordination Compounds. Anal. Lett. 1972, 5 (7), 497–508. DOI: 10.1080/00032717208064332.
- ↑ Jian, Fangfang; Zhao, Pusu; Wang, Qingxiang Synthesis and crystal structure of a novel tartrate copper(II) two-dimensional coordination polymer: {[Cu2(C4H4O6)2(H2O)2·4H2O}∞]. J. Coord. Chem. 2005, 58 (13), 1133–38. DOI: 10.1080/00958970500148446.
- ↑ 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>.
- ↑ 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>.
External links
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