Ninhydrin Test- Definition, Principle, Procedure, Result, Uses


Ninhydrin test is a simple and widely used chemical test to detect the presence of amino acids, peptides, proteins and other compounds that contain a free amino group. Amino acids are the building blocks of proteins and are essential for many biological processes. They can be found in various sources such as food, body fluids, tissues, and forensic samples.

The ninhydrin test is based on the reaction of ninhydrin, a yellow crystalline compound, with the amino group of the test sample. When heated in the presence of ninhydrin, the amino group undergoes deamination and decarboxylation, resulting in the formation of a deep blue or purple colored complex known as Ruhemann`s purple. The intensity of the color is proportional to the amount of amino acid present in the sample. The color can be measured by a spectrophotometer to quantify the amino acid concentration.

The ninhydrin test is useful for both qualitative and quantitative analysis of amino acids and other compounds with an amino group. It can also be used to distinguish carbohydrates from amino acids, as carbohydrates do not react with ninhydrin. However, some exceptions exist, such as proline and hydroxyproline, which produce a yellow-orange color instead of purple. Similarly, some proteins with a free amine group like asparagine produce a brown color.

The ninhydrin test is easy to perform and requires only a few reagents and equipment. It is also sensitive and can detect traces of amino acids in various samples. The ninhydrin test has many applications in biochemistry, forensic science, chromatography, and peptide synthesis. In this article, we will discuss the definition, principle, procedure, result, uses and limitations of the ninhydrin test in detail.