Laboratory test for protein: 7 easy protocol

Laboratory test for protein includes various qualitative test which indicates the presence of proteins. It has certain functional groups which can react to produce characteristically colored products. There are various tests for indicating protein in the given samples. Let us study more about those tests with the easy protocol.

Laboratory test for protein

Laboratory test for protein

Protein can be tested by different protocols and methods. First, let us know a few things about proteins. What exactly are proteins? Living things contain chemical molecules called proteins. They perform several different tasks, such as organizing, transportation, and defense. A protein can have up to four different structural levels and is made up of chains of amino acids. Examples of particular proteins are collagen, insulin, and anticorps. Let us talk one by one :

1. Biuret test

This test is specific for peptide bonds present in proteins. The substances containing not less than two peptide linkage give this test. For this test, we have some easy protocols that we can easily carry out in the lab :



  1. First, the given sample solution is treated with an alkaline solution of dilute copper sulfate and a few drops of biuret reagent is added and observed.
  2. The presence of violet color indicates the presence of protein in the given samples.
biuret test

2. Ninhydrin test

A chemical test called the ninhydrin test is used to determine whether an analyte in question contains amines or -amino acids. In this experiment, ninhydrin (a molecule with the formula C9H6O4) was used.

This test results from a reaction between ninhydrin and an amino group of free amino acids. Because of ninhydrin’s potent oxidizing properties, amino acids that are exposed to it undergo oxidative deamination, releasing ammonia, CO2, a matching aldehyde, and a reduced form of ninhydrin ( hydrindantin).

ninhydrin test


Take 1 mL of the test sample in a dried test tube.
add 10 drops of ninhydrin reagent and hold the test tube on the flame till boiling.bluish-purple color is seenPresence of protein
ninhydrin test

3. Xanthoproteic test

Tyrosine, tryptophan, and phenylalanine are among the amino acids having aromatic nuclei that can be detected using the xanthoproteic test in protein solutions by heating them with concentrated HNO3. Tyrosine or tryptophan will produce a yellow solution when nitric acid is added to a sample and the mixture is heated.

xanthoproteic test


Take a clean test tube and a few drops of concentrated sulfuric acid is added and shake the test tube.
Then gently heat the solutionthe appearance of a yellow colorpresence of amino acids in the protein
xanthoproteic acid

4. Million’s test

Proteins containing phenolic amino acids can give Millon’s test. This test is not provided by gelatin. When proteins are treated with million’s reagents, a white precipitate first forms, and when this precipitate is heated, it turns brick-red, confirming the existence of proteins.

Tyrosine produces a yellow precipitate of mercury-amino acid complex when it reacts with acidified mercuric sulfate solution. The yellow mercury-amino acid combination transforms into the red mercury phenolate upon the addition of sodium nitrate solution and heating.

Million's test


2-3 drops of million’s reagent are taken in a test tube containing the samplewhite ppt is seen
then the sample is heatedafter heating, it turns into brick red coloredindicates the presence of protein
million's test

5. Pauly reaction test

This test is specific for the protein containing tyrosine and histidine. Tyrosine or histidine can be found in proteins via the Pauly reaction, a chemical test. Hermann Pauly, a German chemist who first reported the reaction, is honored with its name. When proteins having either tyrosine or histidine react with diazotized sulfanilic acid in an alkaline solution, a coupling reaction results in the formation of red color.

Pauly test


Test tube + chilled sulfanilic acid+ few drops of pre-chilled sodium nitritecolor begins to appear
Then 1 mL of sample is added and a few drops of sodium carbonate drop by drop is addedthe red colored complex is seenpresence of protein
pauly's test

6. Lead sulfide test

This test is used for the specific detection of amino acids like cysteine and cystine. Detection of amino acid containing sulfur, S-S group in cysteine, and S-H group in cystine.

lead acetate test
2 mL of the amino acid solution is taken along with 2mL of sodium hydroxide
The solution is boiled and cooled down then, a drop of lead acetate is addedthe solution turns black (ppt)presence of cysteine and cystine
lead acetate test

7. Nitroprusside test

This test is especially used to detect the presence of cysteine in the protein sample.

nitroprusside test
2mL of amino acid is taken and 0.5 Ml freshly prepared sodium nitroprusside is added
Now 0.5 concentrated NaOH is addedthe red colored complex is observedpresence of cysteine in the given protein sample
nitroprusside test

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