1) Ninhydrin Test:
Amino acids & peptides, proteins give blue to violet colour with ninhydrin solution.
2) Biuret Test:
Biuret is a compound formed by heating 2 moles of urea at 180°C (shown aside). When biuret is treated with dilute copper sulphate in alkaline medium, purple colour is Acquired. Biuret test widely used for the Recognition of proteins and peptides.
3) Xanthoproteic Test:
Xanthoproteic Test is given by (proteins & peptidÄ—s) which have (aromatic amino acids) phenylalanine or tyrosine or tryptophan in their molecules. On treatment with conc. nitric acid, these amino acids Pass off nitration in the aromatic ring. These nitro compounds (Particular nitrophenols) are yellow in colour. Same reaction which occurs when skin comes in contact with concentrated nitric acid in laboratories.
4) Millon's Test:
When proteins or peptides are treated with Millon's reagent (a solution of mercuric and mercurous nitrate in nitric acid) a white precipitate is formed. When this is heated, a red coloured precipitate is formed. This test is given only by proteins containing tyrosine in their molecules, forming red mercury complexes with the nitrophenol formed. Test is also given by other phenolic compounds and is therefore not Conspicuous to proteins.
5) Sodium Nitroprusside Test:
Sodium nitroprusside reagent gives a red colour with peptides and proteins , which yield cysteine or cystine on hydrolysis. As many proteins consist cysteine or cystine, test is given by most proteins.
6) Sakaguchi Reaction:
Sakaguchi test is a specific reaction for the presence of arginine in proteins. Protein hydrolysates will produced red colour with α-naphthol-sodium hypochlorite reagent if arginine is present. Reaction is due to present of guanidine group.
7) Hopkins-Cole Reaction:
This test is carried out by adding glacial acetic acid then concentrated sulphuric acid to a solution of protein. Violet colour is produced if tryptophan is presence in protein. Reaction is due to glyoxalic acid formed on acid hydrolysis of tryptophan.
* Presence of proteins in urine can be detected by the following
A. Sulphosalicylic Acid Test:
In a test tube, 5ml of the protein solution is taken and added with sulphosalicylic acid drop by drop, and mixed after each addition. Creation of a white precipitate or Squalidity indicates the presence of protein.
B. Heller's Test:
In a test tube, 3ml of concentrated nitric acid is taken. The test tube is inclined and 3ml of the protein solution is added along the test tube wall.White precipitate formed at the junction of the two fluids Signalize presence of protein.
C. Heat Coagulation Test:
Two-third of the test tube is filled with the protein solution and 4-5 drops of chlorophenol red is added with thorough mixing. Purple red colour develops. 1% acetic acid is added drop by drop until the colour changes to a faint pink. The test tube is held at its bottom in slightly inclined position and the upper portion of the fluid is heated. Formation of a dense coagulum occurs in the upper part of the solution. Positive results are obtained for heat coagulable proteins, albumin, and globulin.
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