Objective
Seliwanoff’s test is a biochemical test devised by the Russian chemist Theodore Seliwanoff in 1887. The main objective of the test is to distinguish Aldoses from ketose sugars. If the sugar contains a ketone group, it is a ketose while if it contains an aldehyde group, it is an Aldose.
Principle
The test relies on the principle that on treatment with acid, ketoses are more rapidly dehydrated than Aldoses. The acid hydrolysis of polysaccharide and oligosaccharide ketoses yields simpler sugars followed by furfural. The dehydrated ketose then reacts with two equivalents of resorcinol in a series of condensation reactions to produce a molecule with a deep cherry red color.
When Seliwanoff reagent is added to a solution containing ketoses, a red color is formed rapidly indicating a positive test. When added to a solution containing Aldoses, a slower forming light pink is observed instead.
Seliwanoff’s Reagent
- Test solution: 5% Glucose, 5% Sucrose, 5% Fructose
- Seliwanoff’s reagent (0.5% resorcinol in 3N HCl)
- Water bath
- Pipettes
- Dry test tubes
Procedure
- Take 1ml of sample in test tube and take 1ml of distilled water in another tube as control.
- Add 3ml of Seliwanoff’s reagent in both test tube
- Keep the test tubes in water bath for between 1-2 minutes.
- Look for the development of red color.
Note: If the reaction is allowed for longer time, Aldoses also produce positive results.
Seliwanoff’s Test Result Interpretation
- Positive Seliwanoff’s Test: If the color changes to red, then your result is positive and keto sugar (Fructose and Sucrose) is present inside the solution.
- Negative Seliwanoff’s Test: If no red color appears or if a faint pink color appears, you’re your result is negative and Aldose sugar (Glucose) is present in the solution.