Ninhydrin, a tricyclic 1,2,3-trione, is a useful organic building block. It is an amino acid reagent, which reveals latent fingerprints on porous surfaces like paper, cardboard and raw wood.
It is employed for nitrite detection in various samples, identifying contamination, and is also used as a colorimetric reagent.

Ninhydrin (Triketohydrindene hydrate) may be used as a reagent for the quantification of amino acids and peptides by photometric method and colorimetric method. It may be used to prepare the ninhydrin reagent, by mixing ninhydrin and hydrindantin (reduced form of ninhydrin) in dimethyl sulfoxide. This reagent is used in manual ninhydrin method for the quantitative determination of amino acids.

Used for the detection of free amino groups in amino acids, peptides and proteins.

Used in the detection and assay of peptides, amino acids, amines, and amino sugars yielding highly fluorescent ternary compounds with aldehydes and primary amines. Reaction with sarcosine or proline gives azomethine ylides.