Barfoed's Test for Monosaccharides

Barfoed's test used to distinguish the monosaccharide and disaccharide. Monosaccharides oxidized by Cu 2+ ions form a carboxylic group and precipitation of copper (I) oxide that has brick red color. A positive results of the test is indicated by the appearance of brick red precipitate. This reaction occurs under acidic conditions (pH about 4.6), so acetic acid is used in barfoed reagent. Negative results characterized by remaining blue color of solution after boiling.

Reducing disaccharide like maltose also can react with barfoed reagent (produce red precipitate anyway) but in longer warm-up time. Therefore, the timeliness of this test is very important to produce valid results. NaCl and some other substances can become an obstacle in the reaction.

Barfoed's test reaction

Barfoed's test was discovered by the Danish chemist named Christen Thomsen Barfoed, immortalized his name became the name of this test.

Material and reagents:

• Barfoed reagent: 33 g of copper acetate in 1% acetic acid solution (5 ml of glacial acetic acid in 500 ml of distilled water)
• Material to be tested

Work steps:

• Enter 5 ml of barfoed reagent into a test tube.
• Add 1 ml of material to be tested into test tube.
• Heat tubes in boiling water (water bath) for 1 minute.

Note:

Reagents barfoed not stand with storage for a long time, so it better be made shortly before the time of test.
Reducing disaccharide can show a positive result with the barfoed's test when heated more than 1 minute. Therefore, the time of heating (1 minute) is very important in barfoed's test.