Ninhydrin Reaction

**Ninhydrin reaction (HNR)** is a method for determining the presence or absence of a primary or secondary amide bond in proteins and other organic compounds. The reaction is based on the ability of ninhydrin, an oxidized form of the amine oxide N-chlorosuccinimide (NCS), to form colored complexes with amino acids and their derivatives. If amino groups are present in a molecule of a protein or other organic compound, they will condense with ninhydrin, forming a colored compound with a certain shade. Therefore, the ninhydrin reaction is used to determine the structural features of proteins and to analyze the dynamics and purity of reagents in biological systems.

To carry out the ninhydrin reaction, the following steps must be followed:

1. Prepare a solution of ninhydrin and add it to the test sample. 2. Stir the contents of the solution for a certain time. 3. Leave the mixture for several hours or days - it depends on the specific instructions. 4. Evaluate the resulting color of the solution and compare it with the typical pattern on samples where the amino group is present or absent. The advantages of using the ninhydrin method over other methods based on the detection of residual acidity (for example, the Sholl method) are as follows:

- The eutrophication of most samples in most cases does not allow them to be examined optically, even with longer immersion times in the solvent. Using the ninhydrogen method, you can avoid problems associated with dilution and parallel acidification of the solution before conducting the study. - The result of spectrophotometric research methods is only the measurement of residual acids. Thus, information about the presence of amides is obtained indirectly, and the value thus obtained may not be directly correlated with the amount of amides detected. This disadvantage is more characteristic of the standard method, the Sholl method, than of the ninhydrogen reaction, which has a clear advantage when studying samples with a high content of residual nitrogen-containing products. It is the result obtained with ninhydrene that gives the specialist an idea of ​​either how high-quality the product he has received (and then he will increase the hydrolysis temperature), or that his resulting product does not contain amides and therefore does not need clarification. Some salts containing amide groups, for example, sodium cyclohexanol indoxyl, have sufficient native absorption in the ultraviolet region at wavelengths from 208 to 270 nm. Sufficiently accurate quantitative results on such groups can be obtained by high-resolution absorption or