Thiol adducts of triphenylcyclopropenylium undergo efficient heterolytic dissociation under conditions of both electrospray (ESI) and laser desorption ionization (LDI) mass spectrometry giving rise to a prominent signal of an aromatic C3Ph3+cation. A functionalized mass tagging reagent, an activated ester carrying an S-linked C3Ph3unit, has been developed and used for the derivatization of amines and their subsequent HPLC/ESI-MS detection in low attomolar amounts.