Objective:

• to detect amino acid tryptophan present in protein

Principle:

The indole group of tryptophan reacts with glyoxylic acid in the presence of conc.  H2SO4 to give a purple colored complex.  Glyoxylic acid is prepared by reducing Oxalic acid with magnesium powder or sodium amalgam. Glacial acetic acid which has been exposed to the sunlight also contains glyoxylic acid and can thus be used for this test.

Reagents:

• 1 % tryptophan, 1 % glycine, 5 % egg white (albumin)
• Adamkevich’s reagent: glyoxylic acid ( prepared by reducing oxalic acid with magnesium powder or sodium amalgam)
• H2SO4
• Dry test tubes
• Pipettes

Procedure

1. Take 2 ml test solution in dry test tube.
2. Similarly, take 1ml distilled water in another test tube as control.
3. Add 1 ml of Adamkiewicz’s reagent, mix well.
4. Now add 1ml conc. H2SO4 along the wall of the test tube.
5. A purple colored ring develops at the interface of two solutions.

Result:

Positive Hopkin’s cole test: purple color at the interface. ( tryptophan and egg albumin)

Negative Hopkin’s cole test: glycine

Adamkiewicz reaction (Hopkin’s-cole test): Objective, Principle, Reagents, Procedure and Result

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