Rapid Furfural Test for Glucose and Fructose

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The rapid furfural test is a type of chemical test which is used to determine the difference between fructose and glucose. The test for rapid furfural is like Molisch’s test however it utilizes concentrated hydrochloric acid instead of concentrated sulfuric acid, and the solution is then boiled. A dilute solution of sugar is added in ethanolic 1-Naphthol as well as concentrations of hydrochloric acid. This solution is then boiled and if a violet colour develops within 30 seconds, it is fructose. If a violet colour isn’t visible within 30 seconds, it is because glucose is present.


The rapid furfural test is a chemical test to determine the distinction between fructose and glucose.

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Principle of Rapid Furfural Test

Dehydration reactions owe to the hydroxyl group of sugar. Concentrated HCl being less abrasive than concentrated sulphuric acids, ketoses are dehydrated (e.g. fructose) more quickly than aldoses, forming the hydroxymethyl furfural. It then is dissolved by a-naphthol and forms an edgy violet-colored complex.

Requirements for Rapid Furfural Test


  • The preparation for Molisch Reagent. Molisch’s Reagent can be prepared by mixing naphthol in 95 percent alcohol.
  • Test Solution
  • concentrated hydrochloric acid.


  • Dry test tubes
  • Test tube stand
  • Pipettes



  1. Separately make sure to fill the four tubes of test with 2mL pure water and sugar testing solutions. Include six drops of Molisch Reagent in each tube.
  2. When you hold the test tube at an angle, pour 3ml of concentrated HCL on the tube’s wall. Make sure to boil the solution for 30 seconds. It’s not recommended mixing the acid in the solution.
  3. The heat generated by the reaction could ignite the carbohydrate, leading to an erupting black ring if acid isn’t delivered gradually enough.
  4. In the interface between the acid and the solution inside the test tube, look for the formation of purple-colored circle.


A rapid positive reaction to the furfural test is shown by the appearance of a violet-colored color. The development of violet color within 30 seconds after boiling indicates the presence of a ketosugar, e.g. fructose.

Rapid Furfural Test for Glucose and Fructose
Rapid Furfural Test for Glucose and Fructose

Aberrant reaction

In the rapid furfural test when red color appears instead of violet due to the charring effect of acid dilute the sugar sample using water and test using the dilute sugar solution.

Rapid Furfural Test for Glucose and Fructose
Rapid Furfural Test for Glucose and Fructose


  • The Rapid furfural test is utilized to determine the presence of ketoses.
  • Fast furfural test to distinguish ketoses and aldoses.

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