Seliwanoff's Test For Ketose Sugars

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

Work steps:

• 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.

Note:

This test was discovered by Russian chemist named Theodore Seliwanoff in 1887. This test is popularly used in the test carbohydrate qualitatively, to determine the type of sugar that were tested include ketose or aldose. When showing cherry red color solution, it means sugar that be tested is / contains ketose sugars. 

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