Benedict’s test is used as a simple test for reducing sugars. A reducing sugar is a carbohydrate possessing either a free aldehyde or free ketone functional group as part of its molecular structure. This includes all monosaccharides (eg. glucose, fructose, galactose) and many disaccharides, including lactose and maltose.
Benedict’s test is most commonly used to test for the presence of glucose in urine. Glucose found to be present in urine is an indication of Diabetes mellitus
Benedict’s solution (fresh; certainly not more than 3 months old), Dropper, Test-tube, Test-tube holder. Spirit lamp, Match box, Kidney tray, containers.
Quality checking of the Benedict’s solution
Benedict’s solution is blue in color. In order to check purity of Benedict’s solution take 5 ml of Benedict’s solution in test tube and heat it. If it does not change color, it means, it is pure. Spirit lamp, Match box, Kidney tray, Container.
· Take 5 ml (one teaspoon) of Benedict’s solution in the test-tube.
· Holding the test-tube with the holder, heat it over a spirit lamp till the Benedict’s Solution boils without overflowing.
· Drop 8 to 10 drops of urine into the boiling Benedict’s solution.
· After again boiling the mixture, let it cool down.
· While cooling, the mixture changes color.
· Observe the color change and precipitate formation and analyze the test result
The colour of the mixture serves as a guide to the amount of sugar in the urine :
· Fill three-fourth of a test tube with filtered urine (filtering removes pus if present).
· See the reaction of the urine is acidic. If found alkaline, add one drop of acetic acid and make it acidic.
· Heat the upper third of the urine over sprit lamp and allow it to boil.
· A cloud may appear either due to phosphate or albumin.
· Add acidic acid drop by drop in to the test tube.
· If the urine is still cloudy it indicates the presence of albumin.
· If it becomes clear it indicates the presence of phosphates.
· No albumin is presence in the normal urine.
· If the urine is highly acidic or highly alkaline, the reading will be false.
· Take 5 ml of urine in a test tube and saturate it with ammonium sulphate.
· Add a small crystal of sodium nitroprusside and mix well.
· Slowly run along the side of the test tube liquor ammonia to form a layer.
· Immediate formation of a purple permanganate colored ring at the junction of the two fluids indicates a positive test
· Keep reagent tables in a cool, dry place at a temperature below 860 F(30o C).
· Do not refrigerate the reagent tablets and strips.
· Keep the container tightly closed.
· Do not use discolored or outdated tablets or strips.
· Take a test tube, half full of urine.
· Sprinkle sulphur powder on the surface of the urine.
· If the powder sinks down to the test tube, it indicated the presence of bile salts.
· This is because, bile salts reduce the surface tension of the urine and allows the sulphur powder to sink down.
· Fill three-fourth of a test tube with urine.
· Add iodine drops along the sides of the test tube, so as to form the layer on the surface of the urine.
· A green color at the junction of the two liquids indicates the presence of bile pigments.
· Discard the urine and clean the test tube.