FEHLING SOLUTION B

Fehling Solution B is an alkaline reagent used with Fehling Solution A for detecting reducing sugars and distinguishing reducing from non-reducing carbohydrates. It is also used in Fehling’s test to differentiate compounds based on their reducing properties.
The assay is based on the capacity of sugars with a free aldehyde or keto group to reduce copper(II) ions in a basic solution. Upon mixing the two solutions, Fehling’s solution reacts with the test solution, and on heating, reducing sugar reduces the deep blue solution of copper complex to insoluble cuprous oxide, which has a yellow, red, or orange color. Glucose, galactose, fructose, lactose, and maltose may yield positive results, whereas sucrose typically does not.
Fehling’s test may be used for detecting glucose in urine and for measuring reducing sugar during starch hydrolysis and in the production of glucose syrups and maltodextrin. Alkaline medium is essential for the reaction to take place, acid medium can retard the reduction of copper ions. Aromatic aldehydes are in general not reliably detected by this test.
Fehling Solution B is specified as a colourless solution and passes suitability testing as a reagent for reducing sugars. Proper laboratory procedures should be followed during preparation and testing.

Used with Fehling’s Solution A to detect reducing sugars through formation of coloured cuprous oxide precipitate.