Which compound is typically formed during the treatment with Ninhydrin?

Ruhemann's Purple is the compound that is typically formed during the treatment of latent fingerprints with Ninhydrin. Ninhydrin reacts with amino acids that are present in sweat residues left by friction ridges on skin. When Ninhydrin interacts with these amino acids, it undergoes a chemical transformation that leads to the formation of Ruhemann's Purple, which is a deep blue-purple compound. This coloration not only helps in visualizing the fingerprints but also serves as an indicator of the presence of amino acids, thereby enhancing the detection process of latent prints on various surfaces.

Other compounds listed, such as Gentian Violet, Naphthalene Black, and Amido Black, are used in different contexts within forensic science and latent print visualization, but they are not products of the Ninhydrin treatment process. Gentian Violet is often used as a dye in various applications, including biological staining, while Naphthalene Black and Amido Black function primarily as colorimetric agents for protein detection. Thus, the formation of Ruhemann's Purple is a specific and well-documented outcome of Ninhydrin treatment that is critical for enhancing the visibility of latent prints.