4-(Dimethylamino)benzaldehyde (DMAB or Ehrlich’s reagent) has been used as a color reagent for the determination of hydroxyproline level.
[1]It forms colored condensation products (Schiff bases) with pyrroles and primary amines. DMAB is also suitable as a reagent to develop latent fingermarks on paper surfaces yielding impressions that are both colored and photoluminescent.