Xanthoproteic test

Dr. Brown agrees that the Xanthoproteic test indicates the presence of protein. She reminds you that this test specifically detects the presence of aromatic amino acids (e.g. tyrosine, tryptophan, phenylalanine). This makes it less ideal than another test, which can detect all proteins in the urine sample. 

You take this opportunity to revise this test and note the following procedure in your notebook. 

1. To 3 ml of 1% egg albumin (protein sample) add 1 ml of concentrated nitric acid. A white precipitate should appear. 

2. Boil until the solution is yellow. 

3. Cool and add 2 ml of concentrated 40% NaOH to give an orange color. This indicates the presence of protein, as shown in the image below (right tube). The left tube indicates a negative test.  

Website: http://biocheminfo.com/2020/04/04/xanthoproteic-test-principle-reaction-reagents-procedure-and-result-interpretation/  

Dr. Brown asks you to re-consider your answer. You think a video may also help you understand the xanthoproteic test further.