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Barfoed’s Test for Monosaccharides

Barfoed’s test for monosaccharides post we briefly summarises about: principle, reagents requirements, barfoed test for carbohydrates procedure, result, application and limitations of Barfoed’s test.

Barfoed’s Test for Monosaccharides

Barfoed test for carbohydrates is a subjective method for determining the presence of Monosaccharide in a solution. The monosaccharide reacts with Barfoed’s reagent, forming a solution.

It also reacts to disaccharide, although the reaction is mild, and monosaccharide may be distinguished from disaccharides and polysaccharides with ease.

Barfoed test for carbohydrates is a chemical test used to determine whether or not monosaccharide is present. It is determined via the reduction of copper (II) acetic acid to copper (I) oxide (Cu2O), which results in a brick red mixture.

Principle

The basis of Barfoed’s test reaction is the reduction of cupric acetate by reducing monosaccharides and disaccharides. When cupric acetate is converted to cuprous oxide, a brick red precipitate forms.

Monosaccharides react quickly, producing a scarlet precipitate in 1–5 minutes. The reducing disaccharides, on the other hand, require anywhere between 7 and 12 minutes to create a crimson precipitate.

The reaction with disaccharides is slower because they must first be hydrolyzed before interacting with the reagent cupric acetate to create cuprous oxide.

RCHO +2 CU2+ +2H2O―> RCOOH + Cu2O + 4H+

Requirements

Reagent

1. Barfoed’s reagent: 0.33M solution of copper acetate is added to 1% acetic acid. The freshly prepared reagent should be used for the assay.

Materials

1. Test tubes

2. Test tube stand

3. Pipettes

Equipment

1. Water bath

2. Vortex

Procedure

1. 1 mL of a given sample should be placed in a clean, dry test tube. If disaccharides are employed, their concentration should not exceed 1% (w/v).

2. In a separate tube, control 1 mL of pure water. Add a few drops of Barfoed’s reagent to both tubes and vortex them together.

3. Allow 1-2 minutes for the test tubes to soak in the water bath. Boiling should not last longer than 2 minutes, or the disaccharides may hydrolyse into monosaccharides, resulting in a positive result.

4. Examine how the colour appears in the test tubes. kept track of how long it took for colour to show in the tubes.

Result

Barfoed's Test for Monosaccharides

Brick Red precipitation within 5min boiling in case of a monosaccharide, while 7-12 min for disaccharide. This delay in the development of the color of in case of disaccharides is due to slow reduction of disaccharide during the reaction.

Applications

1. Barfoed test for carbohydrates is used to identify reducing monosaccharides and distinguish the reducing disaccharides from reducing monosaccharides.

Limitations

1. Barfoed test for carbohydrates  cannot be used to detect sugar in urine as urine contains Cl- ions, which might interfere with the reaction. If a higher concentration of disaccharides is present in a sample, it might give a positive result.

Further Readings

Reference