Principle of Seliwanoff’s test

Seliwanoff’s test is used for difference between ketose and aldose sugars. It is for the detection of fructose i.e this test is positive for fructose and negative for other sugar. With the help of this test we can easily distinguish and detect fructose solution.

When the saliwanoff’s reagent is mixed with sugar solution, it will give color for keto group.

Reagents for seliwanoff’s test:

• Saliwanoff’s reagent (recicinal plus hydrochloric acid)
• Original solution

Procedure of Saliwanoff’s test:

• Take 3ml of salwenoff’s reagent in the test tube.
• Then add 3 drops of original solution in the test tube.
• Heat the mixture.
• If red colour appear, then it shows that keto group or fructose is present in the original solution.

Precautions:

Here are some of the things that you need to take care of while performing this test:

1. Add seliwanoff reagent more then the solution as mentioned above in the procedure.
2. Heat the solution carefully.
3. Keep the test tube to side while heating. It should not be towards any human.
4. Remove the test tube from fire when the solution boils the the opening of test tube. Place it again when it goes down.

Some important points about seliwanoff’s test:

Here are some of the important things about seliwanoff’s test that you must remember while performing the test:

• First polysaccharides or oligosaccharides are hydrolyzed to simple sugar by acid hydrolysis.
• Simple sugars then react with recicinal to produce deep red color.
• Aldose sugars will not react will recicinal and produce a faint pink colour.
• Recicinal reacts with only fructose and sucrose. (As sucrose contains fructose and glucose, seliwanoff’s reagent react with its fructose part).
• All other sugars except fructose and sucrose gives negative result with saliwanoff’s reagent.

Conclusion:

If you follow the step by step procedure written above correctly keeping the precautions in mind then you would see the color of solution changing to red if your solution contains keto sugar.

You can also test it for aldose sugar and see yourself the negative results. It would produce a light pink solution as mentioned above.