Take 1 ml of the sample extract or test solution in a test tube. Add 4 - 5 drops of iodine solution to it and mix the contents gently. Observe if any colored product is formed.
Note the color of the product. This test is used for distinguishing monosaccharides from reducing disaccharides. Monosaccharides usually react in about 1 - 2 min while the reducing disaccharides take much longer time between 7 - 12 min to get hydrolysed and then react with the reagent. Brick red color is obtained in this test which is due to the formation of cuprous oxide.
Keep the test tubes in a boiling water bath. A briskly boiling water bath should be used for obtaining reliable results. Look for the formation of brick red color and also note the time taken for its appearance. This test is used to distinguish aldoses from ketoses.
Ketoses undergo dehydration to give furfural derivatives, which then condense with resorcinol to form a red complex. Prolonged heating will hydrolyze disaccharides and other monosaccharides will also eventually give color. Note for the appearance of a deep red color. This would indicate that the sample solution contains a keto sugar.
Formation of yellow or red ppt of cuprous oxide denotes the presence of reducing sugars. Rochelle salt acts as the chelating agent in this reaction. Mix thoroughly and place the test tubes in vigorously boiling water bath.
Download Now Download to read offline and view in fullscreen. Business , Technology. Download Now Download Download to read offline. Kate Alyssa Caton Follow. Qualitative tests for carbohydrates. Bial's Test. Mucic and Barfoeds Test. Osazone test. What to Upload to SlideShare. Related Books Free with a 30 day trial from Scribd.
Related Audiobooks Free with a 30 day trial from Scribd. Elizabeth Howell. Ma Theresa Diane Adawe. Cicilia Kalekye. Yokesh Frantic. Ashish Kumar. Jordan Precious. Jann Reynard Cloma. Jane Zyreel Sumangil. Bhavya Vijayakumar. Tony Thomas. Radish White. Collins Agyemang Acheampong. Show More. Views Total views. Actions Shares. No notes for slide. Seliwanoff 8. A few drops of the reagent, consisting of resorcinol crystals dissolved in equal amounts of water and hydrochloric acid, are heated with the test solution and the formation of a red precipitate indicates a positive result.
The dehydrated ketose then reacts with the resorcinol to produce a deep cherry red color. Aldoses may react slightly to produce a faint pink color. Carbohydrates are mainly divided into monosaccharides, disaccharides and polysaccharides.
The commonly occurring monosaccharides includes glucose, fructose, galactose, ribose, etc. The two monosaccharides combine together to form disaccharides which include sucrose, lactose and maltose. Starch and cellulose fall into the category of polysaccharides, which consist of many monosaccharide residues.
This is a common test for all carbohydrates larger than tetroses. The test is on the basis that pentoses and hexoses are dehydrated by conc. Sulphuric acid to form furfural or hydroxymethylfurfural, respectively. This forms the reduction test of carbohydrates.
Hence, formation of the yellow or brownish-red colored precipitate helps in the detection of reducing sugars in the test solution. Depending on the concentration of sugars, yellow to green color is developed.
All monosaccharides are reducing sugars as they all have a free reactive carbonyl group. Some disaccharides, like maltose, have exposed carbonyl groups and are also reducing sugars, but less reactive than monosaccharides. Barfoed's test is used to detect the presence of monosaccharide reducing sugars in solution.
0コメント