Barfeod’s test is a qualitative test used to check the presence of monosaccharides in an unknown solution.Barfeod’s reagent react with monosaccharide and precipitate is formed.It also react with disaccharide but the reaction is slow and monosaccharides can be easily distinguished from disaccharides and polysaccharides.
Principle of barfoed’s test:
When barfoed reagent mix with solution of monosaccharide or disaccharide, and heated in boiling water bath, they react and crystal precipitate is formed. Copper acetate which is present in barfoed’s reagent convert to copper oxide and give brick red precipitate when react with monosaccharide or disaccharides.Monosaccharde react fast while disaccharide react slowly.
Reagents for barfeod test:
3 to 5 ml of barfoed’s reagent which is composed of:
- Copper acetate
- Acetic acid.
Original sugar solution.
Procedure of barfeod’s test:
- Take 3 to 5 ml of barfoed’s reagent in a test tube.
- Add 3-4 drops of original solution to the test tube.
- Then put the test tube in boiling water bath for boiling.The reaction will occur and precepitate would be formed.
Monosacchardies give brick red precipitate with copper acetate and acetic acid.They usually appear within seven minutes.If they appear within seven minutes, it means that monosaccharide is present in the solution.If brick red precipitate are formed after seven minutes, it means that disacchaides are present in the original solution.And if precipitates are not formed, it means that solution doesn’t contains either monosaccharides or disaccharides.
Here are a few important things you must keep in mind while performing this test:
- Add more amount of barfoed reagent as compared to solution. As mentioned in procedure above.
- Keep a stop watch or just watch with yourself and note time when you put test in boiling water bath.
- Water should be boiling. Don’t put test tube in water if it is not boiling.
- Remove the test tube regularly and check if precipitates are formed or not. If ppt are not formed, keep it in water bath again quickly.
Results of barfoed test:
If precipitate appear in 7 minutes, it means monosaccharde is present in the original solution.But if precipitate appear after seven minutes, it means that disaccharide is present in the original solution.