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Picric Acid Test for Glucose – Principle, Procedure, Result

Picric acid test is used for reducing sugars, and is a highly sensitive chemical tests. Picric acid reactions (toxic yellow crystal solid) which is also referred to chemically as 2,4 6-trinitrophenol (TNP) reacts with sugars that are reduced to create Picramic Acid that is red-colored.

The Picric Acid test is made up of a sugar that has functional ketone or free aldehyde groups within its molecular structure, which acts as an agent to reduce. Examples include fructose, glucose and lactose. maltose and arabinose. except for sucrose.

Principle of Picric Acid Test

The Picric Acid reaction can be described as a sensitive chemical test to determine the presence of reducing sugars in carbohydrates. Picric Acid (toxic Yellow crystal solid) is also known as chemically as 2,4,6 trinitrophenol (TNP) Picric acid reaction occurs when there are present reducing sugars and results in Picramic Acid which is red-colored.

Reduced properties are observed in the monosaccharides and disaccharides which have a free aldehyde or ketone. Reduced sugars contain the free aldehyde or ketone group with the capability of reducing.

In an alkaline environment, they reduce the organic acids in various forms. In order to make the solution alkaline, basic sodium carbonate (Na2CO3) is added. Picric acid (yellow solution) is converted to picramic acid via reducing sugars (mahogany the red solution).

Principle of Picric Acid Test
Principle of Picric Acid Test | Source: https://www.biosciencenotes.com/wp-content/uploads/2018/11/picric-1.png

Requirements

Materials

  • Boiling water bath
  • Pipette
  • Test tube
  • Test tube stand

Chemicals

  • Picric acid
  • Sodium Carbonate

Picric Acid

  • Saturated picric acid: Dissolve 13 mg picric Acid in 100mL Double distillated water, then boil the solution and then allow to cool.
  • 10% Sodium Carbonate: Dissolve 10 grams of Sodium Carbonate in 50 mL water, dilute it with water to 50 mL, then mix.

Procedure of Picric Acid Test

  1. Add 1mL of the above reagent to 1mL of the test solution followed by 0.5 mL of 10% Sod. Carbonate solution.
  2. Heat the test tube in a boiling water bath.
  3. Observe the color of the solution.

Result of Picric Acid Test

Positive result in the picric acid reaction is the appearance of a mahogany red colour in the solution. This is a sign of the presence of reducing sugar within the solution.

Result of Picric Acid Test
Result of Picric Acid Test | Image Source: https://www.biosciencenotes.com/wp-content/uploads/2018/11/picric1.png.jpg

Application of of Picric Acid Test

Picric acid test is used to detect the reducing sugars. Mahogany red solution is the positive result. A compound (here sugar, saccharides or sugar) that has the free aldehyde or ketone group can have reduction properties. When they are in an alkaline solution they can reduce organic acids. To make the solution more alkaline (or basic), Sodium Carbonate (Na2Co3) can be added. In the process, reduced sugars transform Picric Acid reaction (yellow solution) to picramic acid (mahogany red solution).

Refereneces

  • http://www.expertsmind.com/questions/define-observation-or-inference-for-picric-acid-test-30180046.aspx
  • https://studylib.net/doc/6662411/carbohydrates-tests-2
  • https://noteshippo.com/picric-acid-test-for-reducing-sugars-principle-procedure-observation/
  • https://www.biosciencenotes.com/picric-acid-test-for-the-detection-of-reducing-sugars/

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