FEHLING SOLUTION A

Fehling Solution A is used with Fehling Solution B to detect reducing sugars, particularly monosaccharides such as glucose. The reagent is an important component of Fehling’s test, which identifies sugars based on their reducing properties.
The reaction is influenced by whether there is a free aldehyde or keto group in the sugar structure. Fehling Solution A supplies the necessary copper(II) ions required for the reaction. With the addition of Fehling Solution B and a sugar containing sample at an alkaline pH, reducing sugars reduces the copper(II) ion to an insoluble cuprous oxide. Depending on the reaction and the concentration, this will result in a yellow, orange or red-coloured precipitate.
Glucose, galactose, fructose, lactose, and maltose can produce positive reactions, while sucrose generally does not. The test is applicable for glucose estimation in urine to screen for glucosuria and for assessing reducing sugar levels during starch hydrolysis and in the manufacture of glucose syrup.
Fehling Solution A has a clear blue-coloured appearance and passes suitability testing as a reagent for reducing sugars. The reaction requires alkaline conditions. Acidic conditions can interfere with copper ion reduction and may lead to unreliable results. Aromatic aldehydes are generally not detected using this test.
Proper laboratory practices should be followed during handling and testing.

Detects reducing sugars, including glucose, through a characteristic coloured cuprous oxide precipitate in an alkaline reaction.