Ninhydrin (2,2-dihydroxyindane-1,3-dione) is a chemical used to detect ammonia or primary and secondary amines. When reacting with these free amines, a deep blue or purple color known as Ruhemann's purple is produced.
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.