Detection Of Reducing Substances In Urine And Faeces
INTRODUCTION:
Benedict's reagent (also called Benedict's solution or Benedict's test) is a chemical reagent named after an American chemist, Stanley Rossiter Benedict. Benedict's reagent is used as a test for the presence of reducing sugars. This includes all monosaccharides and the disaccharides, lactose and maltose. Even more generally, Benedict's test will detect the presence of aldehydes (except aromatic ones), and alpha-hydroxy-ketones, including those that occur in certain ketoses. Thus, although the ketose fructose is not strictly a reducing sugar, it is an alpha-hydroxy-ketone, and gives a positive test because it is converted to the aldoses glucose and mannose by the base in the reagent. Benedict's reagent contains blue copper(II) ions (Cu2+) which are reduced to copper(I) ions (Cu+). These are precipitated as red copper(I) oxide which is insoluble in water. Benedict's solution, deep-blue alkaline solution is used to test for the presence of the aldehyde functional group, -CHO. Wee-Tab Benedict’s Tablet is a solid form of the reagent that provides comparable results as the reagent.
PRINCIPLE:
The substance to be tested is heated with the Wee-Tab Benedict’s Tablet in the provided heat stable test tube; formation of a brick-red precipitate indicates presence of the aldehyde group. Since simple sugars (e.g., glucose) give a positive test, the tablets are used to test for the presence of glucose in urine, a symptom of diabetes. Once a reducing sugar is detected in urine, further tests have to be undergone in order to ascertain which sugar is present. Only glucose is indicative of diabetes. Wee-Tab Benedict’s Tablet reacts chemically like Fehling's solution; the cupric ion (complexed with citrate ions) is reduced to cuprous ion by the aldehyde group (which is oxidized), and precipitates as cuprous oxide, Cu2O.
INGREDIENTS:
Wee-Tab Benedict’s Tablet (Cat No. KS-K1965) contain sodium carbonate, sodium citrate and 2 mg. copper(II) sulfate pentahydrate.
STORAGE:Store tablets at room temperature away from light.
MATERIALS REQUIRED:Wee-Tab Benedict’s Tablet are sold in tubes ready-to-use, 50 per pack. The test requires fresh urine samples since bacteria consume glucose and other reducing sugars. Refrigerate urine samples if they cannot be tested immediately. The following items are required but not provided:o Disposable pipetteo Water bath/Heating Blocko Glass Tubes
DIRECTIONS FOR USE:
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Add 10 drops of urine to the heat stable test tube containing the tablet. Addition of water is not required for urine sample testing.
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Heat in a water bath at 100oC for 10-15 minutes.
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Compare color of liquid to provided color chart to determine glucose content.
INTERPRETATION:
The solution should progress in the colors of blue (with no glucose present or negative), green, yellow, orange, red, and then brick red or brown (with high glucose present). A color change would signify the presence of glucose. The common disaccharides lactose and maltose are directly detected by Wee-Tab Benedict’s Tablet, because each contains a glucose with a free reducing aldehyde moiety, after isomerization. Urine samples may begin to react within 30 seconds but should be held for 5 minutes for complete results. Limitation: Leaving samples in water bath for more than 7 minutes may lead to erroneously low results, but the test will not go back to negative. Negative tests will remain negative regardless of time frame.
QUALITY CONTROL:
For positive control, make a 2% dextrose solution in water. Add 5 drops of the solution and 5 drops of water to the test tube containing the tablet. Results should proceed to a red brick color within 3-5 minutes. Negative control can be done with 10 drops of water only. This should remain blue.
