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Rapid Furfural Test for Glucose and Fructose

Rapid furfural test for glucose and fructose post we briefly summarise about: principle, reagents requirements, procedure, result, application and limitations of rapid furfural test.

Rapid Furfural Test

The rapid furfural test is a chemical method for determining the difference between glucose and fructose. The rapid furfural test is identical to Molisch’s test, except that instead of concentrated sulfuric acid, concentrated hydrochloric acid is used and the solution is boiled.

Objective

The rapid furfural test is a chemical method for determining the difference between glucose and fructose.

Principle

A dehydration reaction which owe to the hydroxyl groups of the sugar. Concentrated HCl being weaker than concentrated sulphuric acid, dehydrate ketoses (e.g. fructose) more readily than aldoses to form hydroxymethyl furfural, which then condenses with α-naphthol to form a violet colored complex.

Requirements

1. Reagent

  1. Preparation of Molisch Reagent, Molisch’s reagent can be made by mixing naphthol with 95 percent ethanol.
  2. Test Solution
  3. H2SO4

2. Materials

  1. Dry test tubes
  2. Test tube stand
  3. Pipettes

3. Equipment

  1. Water bath

Procedure

  1. Separately, fill four test tubes with 2 mL pure water and test sugar solutions. Add six drops of Molisch reagent to each tube.
  2. While holding the test tube in an angled position, pour 3 ml concentrated HCL along the test tube’s wall. Only bring to a boil for 30 seconds. It’s not a good idea to mix the acid with the solution.
  3. The heat created by the reaction may burn the carbohydrates, resulting in a black ring if strong acid is not delivered slowly enough.
  4. At the interface between the solution and the acid in the test tube, look for the formation of a purple-colored ring.

Observation

Rapid furfural test positive reaction is indicated by the development of violet color. Development of violet color within 30 seconds of boiling indicates presence of a keto sugar, e.g. fructose. 

Rapid Furfural Test

Positive rapid furfural test

Aberrant reaction

In rapid furfural test, If red color develops instead of violet color due to charring action of acid, dilute the sugar sample with water and conduct the test with diluted sugar solution.

Rapid Furfural Test

Method to avoid charring response in rapid furfural test

Applications

  1. This Rapid furfural test is used to detect the presence of ketoses.
  2. Rapid furfural test for differentiating ketoses from aldoses.

Further Readings

Reference

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