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Nylander’s Test for Carbohydrates

Nylander’s test for carbohydrates post we briefly summarise about: principle, reagents requirements, procedure, result, application and limitations of Nylander’s test.

Nylander’s Test for Carbohydrates

Nylander’s test is a chemical test used for detecting the presence of reducing sugars. Glucose or fructose reduces bismuth oxynitrate to bismuth under alkaline conditions. When Nylander’s test reagent, which consists of bismuth nitrate, potassium sodium tartrate and potassium hydroxide, is added to a solution with reducing sugars, a black precipitate of metallic bismuth is formed.

Reducing sugar is a type of sugar that acts as a reducing agent and can effectively donate electrons to another molecule by oxidising it. In another definition, reducing sugar is any sugar that tends to act as a reducing agent because it contains either an aldehyde group (-CHO) or a ketone group (-CO-). The Nylander’s test purpose is a that detects the presence of reducing sugars. Under alkaline conditions, glucose or fructose converts bismuth oxynitrate to bismuth.

Nylander’s Test Principle

Free ketone or aldehyde group of carbohydrate reduces to form black precipitates bismuth subnitrate reduced to black bismuth. Even very small amount of glucose (0.08%) can be detected by this test.

Requirements

Materials

  1. Test tube
  2. Test tube stand
  3. Water Bath
  4. Weighing balance

Chemicals

  1. Bismuth Subnitrate
  2. Glucose or Fructose
  3. Potassium Hydroxide
  4. Rochelle salt

Reagent

  1. Nylander’s Reagent Composition: Dissolve 4 gm of Rochelle salt and 2 gm of bismuth subnitrate in 10% solution (100mL) of potassium hydroxide.

Procedure

  1. Take 5 ml sample (Glucose or Fructose) solution in a test tube, add 5–8 drops of Nylander’s reagent, boil for 3 minutes on boiling water bath, and allowed reach room temperature.

Nylander’s Test Positive Result

Nylander’s Test

Nylander’s test positive result color, black precipitates develop after a few minutes (bismuth subnitrate reduced to black bismuth).

How to Test For Carbohydrates?

Take 5 ml sample (Glucose or Fructose) solution in a test tube, add 5–8 drops of Nylander’s reagent, boil for 3 minutes on boiling water bath, and allowed reach room temperature. Make a note of any changes.

Further Readings

Reference

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