Tryptophan is an amino acid. Hopkins Cole test is a specific test used for the detection of tryptophan. When tryptophan is present in a solution, it gives a reddish violet ring.
REAGENTS of Hopkins Cole test:
Hopkins Cole Reagent: Magnesium compound of Glyoxalic acid and concentrated H2SO4.
Concentrated H2SO4 causes dehydration of tryptophan which reacts with Hopkins Cole reagent to give a reddish violet ring between two layers.
PROCEDURE of Hopkins Cole test:
- Add 1 ml of original solution (protein solution) in a test tube.
- Add 1 ml of Hopkins-Cole reagent in the test tube.
- Mix thoroughly.
- Then add 1 ml of concentrated sulphuric acid, pouring it down along the side of the test tube.
A deep violet or purple ring forms at the junction of the two liquids. This indicates the presence of tryptophan.
Gelatin and other proteins which do not contain tryptophan do not give this reaction.
If you follow all the steps mentioned above correctly, then the reddish violet ring will form at the junction of the two liquids. This means that the result is positive and tryptophan is present in the solution.
Below are some precautions which should be followed while performing the experiments.
- Firstly wash the apparatus before and after the experiment keenly.
- Test tube should be free of impurities.
- Carefully measure the solution before pouring it into the test tube.
- Make sure to pour the acids into the test tube sidewise. Otherwise, it will give you a false result.
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