Acree-Rosenheim test: Principle, Reaction, Reagents, Procedure and Result Interpretation

Acree-Rosenheim test 

(Detection of tryptophan)

It is also known as aldehyde test. This test used for detecting the presence of tryptophan in proteins.

Principle:

Acree-Rosenheim is another test for detecting tryptophan (Trp) in a protein solution. Tryptophan is mixed with formaldehyde (CH₂O). Concentrated sulfuric acid is added to form two layers. A violet zone in the junction point of two layers is a positive result. A similar result is obtained by the Hopkins-Cole reaction which is frequently used to detect Trp in a protein solution.

Reaction:

Fig: Acree-Rosenheim reaction with Trp.

Reagents:

1. Test solutions:
   •  Prepare solutions containing 1% individual amino acids such as tryptophan, tyrosine, phenylalanine, glutamic acid, etc.
   • Protein solution: Egg albumin in distilled water (5%-10%).
2. Formaldehyde (CH₂O)
3. Cone H₂SO₄.

Procedure:

• To 1 ml of formaldehyde, add 1 ml of 1% amino acid solution.
• Pour 1 ml H₂SO₄ down the side of the sloping test tube.
• Observe the formation of purple color at the interface between the two layers.

Result Interpretation:

Positive test: Appearance of a purple ring between the two layers due to the presence of tryptophan.

Negative test: No appearance of a purple ring between the two layers due to the absence of tryptophan.

References:

• https://fac.ksu.edu.sa/sites/default/files/Qualitative_tests_of_amino_acids_Lab_1.pdf
• http://www.chem.boun.edu.tr/wp-content/uploads/2014/04/Chem-415-Experiment-2.pdf
• https://www.ukessays.com/essays/biology/quantitative-tests-for-amino-acids-and-proteins-biology-essay.php
• http://www.biologydiscussion.com/proteins/qualitative-and-quantitative-tests-for-amino-acids-and-proteins/13065
• https://vlab.amrita.edu/?sub=3&brch=63&sim=1094&cnt=1