CHEMICAL TEST OF CARBOHYDRATES

This presentation includes chemical test of carbohydrates .
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1. Detection of Carbohydrates Small quantities of aqueous extracts of powdered drug were treated separately with distilled water and filtered. The filtrates were concentrated and used for various tests to detect the presence of carbohydrates. Molisch’s Test The filtrate was taken in a test tube and treated with 1ml of 1% alcoholic α- naphthol solution  2 ml of concentrated sulfuric acid was added along the side of the test tube  Violet color ring at the junction of two liquids indicates the presence of carbohydrate .

2. b) Fehling’s Test Small portion of concentrated extract was taken in a test tube with equal volumes of Fehling’s solution A and B  It was heated on a Bunsen burner. Formation of green, yellow or brick red color precipitate indicates the presence of reducing sugar(s). c) Benedict’s test Small portion of the concentrated extract was treated with equal volumes of Benedict’s reagent and heated  Formation of green, yellow or brick red color precipitate indicates the presence of reducing sugar(s).

3. d) Barford’s Test Small portion of the concentrated extract was treated with equal volumes of Barford’s reagent and heated in a water bath for five minutes. Formation of red color precipitates at the bottom of the test tube indicates presence of monosaccharide(s). e) Cobalt-chloride Test 3 ml of test solution was taken in a test tube and treated with 2 ml of cobalt chloride solution, boiled and cooled. Few drop of sodium hydroxide solution was added. Appearance of greenish blue color indicates presence of glucose/ appearance of purplish color indicates presence of fructose/ upper layer greenish blue and lower layer purplish color indicates presence of glucose and fructose.

4. f) Tollen’s Phloroglucinol Test 2.5 ml of concentrated Hydrochloric acid, 4 ml of 0.5% solution of phloroglucinol and 1-2 ml of test solution were mixed together and heated. Appearance of yellow or red color indicates presence of hexose sugars like galactose . g) Test for Starch A small amount of extract was taken in a test tube and treated with dilute iodine solution. Appearance of blue color indicates presence of starch.