Seliwanoff's test used to distinguish sugars that included
ketose or aldose. Aldose sugars have an aldehyde group, while ketose have a
ketone group. So if heated, ketose is faster dehydrated than aldose. HCl in the
seliwanoff’s reagent will dehydrate sugar into furfural which will react with
resorcinol to form a cherry red solution.
With this test, ketose sugars such as fructose will result in cherry red color, while the aldose sugars like glucose will give a negative result with no red color appearing in the solution. However, if the heating is not in accordance with the procedure (over 5 minutes), aldose sugar will sometimes produce a pink color. While the sucrose (a combination of fructose and glucose) will produce a cherry red color because of the fructose in it.
The reaction occurs:
- HCl dehydrate sugar ketosa forming furfural.
- Furfural reacts with resorcinol (seliwanoff’s reagent) forming the cherry red color of solution.
Material and reagents:
- Seliwanoff’s reagent (Dissolve 34 ml of HCl in 68 ml of distilled water, add 0.15 g resorcinol)
- Material to be tested
- Enter 5 ml of seliwanoff’s reagent into a test tube.
- Add 1 ml of material to be tested.
- Heat in boiling water (water bath) for 5 minutes.
- Observe the color change appears.