Imitation is the Sincerest Form of Flattery

The success of ninhydrin (2,2-dihydroxyindane-1,3-dione) as a method of revealing latent fingerprints by chemically reacting with the free amines present in amino acid residues has created several imitators. A previous entry described the use of DFO (1,8-diazafluoren-9-one) as a substitute for ninhydrin. Along the way I have discovered several more reagents that most likely react in similar way to ninhydrin to form a colored and/or fluorescent compound in the presence of primary amines. 5-MTN (5-methylthioninhydrin) is simply a modified ninhydrin. Fluorescamine has a ketal in a similar position as the ninhydrin gem diol. The two reagents 1,2-indanedione and O-phthaldehyde have reactive carbonyl groups. Dansyl chloride (5-(dimethylamino) naphthalene-1-sulfonyl chloride) is a well know reagent used to modify amino acids to facilitate UV-vis and fluorescent detection of these compounds as they are eluted from an HPLC column. These reagents tend to form more active chromophores and/or fluorescent compounds that can be more easily detected and distinguished from the background than ninhydrin. The detection of amines is an interesting crossover area for fingerprint analysis, chemistry, and biochemistry.

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