4-(Dimethylamino)benzaldehyde is a simple aldehyde which forms colorful Schiff base adducts with amines, pyrroles and indoles, and can be used to assay proteins for residues containing these functional groups. 4-(Dimethylamino)benzaldehyde is often used for the Ehrlich reaction: a test for the presence of indoles in a sample. This reaction with indole is also exploited to indicate the presence of tryptophan residues on proteins.
