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Picric Acid Test for Glucose

Picric acid test for glucose post we briefly summarises about: principle, reagents requirements, Picric acid test procedure, picric acid reaction result, application and limitations of Picric acid test.

Picric Acid Test for Glucose

Picric acid test for reducing sugars and it is highly sensitive chemical test. Picric acid reaction (toxic yellow crystalline solid), also known chemically as 2, 4, 6-trinitrophenol (TNP), reacts with the reducing sugars to generate Picramic Acid, which is red in colour.

Picric acid test is based on, a sugar with free aldehyde or ketone functional groups in its molecular structure that acts as a reducing agent. Examples include glucose, fructose, glyceraldehydes, lactose, arabinose, and maltose, Except for sucrose.

Principle

Picric Acid Test

Picric Acid Reaction: Picric Acid to Picramic Acid

Picric acid reaction is a highly sensitive chemical test for the presence of reducing sugars in carbohydrates. Picric Acid (toxic yellow crystalline solid), also known chemically as 2,4,6-trinitrophenol (TNP), picric acid reaction happens with the reducing sugars to generate Picramic Acid, which is red in colour. 

Reduced characteristics are seen in all monosaccharides and disaccharides that contain a potentially free aldehyde or ketone group. Reducing sugars have a free aldehyde or ketone group that has the ability to reduce. 

When in an alkaline solution, they decrease various organic acids. To make the solution alkaline or basic, sodium carbonate (Na2CO3) is added. Picric acid (yellow solution) is reduced to picramic acid by reducing sugars (mahogany red solution).

Requirements

Materials

1. Boiling water bath

2. Pipette

3. Test tube

4. Test tube stand

Chemicals

1. Picric acid

2. Sodium Carbonate

Picric Acid

1. Saturated picric acid: Dissolve 13 mg Picric Acid in 100mL Double distilled water, boil the solution and allowed to cool.

2. 10% Sodium Carbonate:  Dissolve 10 g of Sodium Carbonate in about 50 mL of water, dilute with water to 50 mL, and mix.

Procedure

1. 1 mL of the Saturated picric acid reaction reagent, followed by 0.5 mL of the 10% sodium carbonate solution, to 1 mL of the sample solution.

2. Heat the tube in a boiling water bath. The presence of sugar reduction in the solution causes a mahogany red colour to develop.

Result

Picric Acid Test

Positive reaction in picric acid reaction is appearance of mahogany red solution colour indicates the presence of reducing sugar in the solution.

Uses

Picric acid test for reducing sugars. Mahogany red solution formation indicates a positive outcome. A compound (here, sugar or saccharides) with a free aldehyde or ketone group has reducing properties. When in alkaline solution, they reduce some organic acids. To make the solution alkaline or basic, Sodium Carbonate (Na2Co3) is added. As a result, reducing sugars convert picric acid reaction (yellow solution) to picramic acid (mahogany red solution).

Further Readings

Reference

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