Experimental and Theoretical Investigation of 5-aminoindole Chemical Ionization

on mobility spectrometry was used for studying chemical ionization of 5-aminoindole. The ionization source was corona discharge in positive mode. Two product ion peaks were observed in the ion mobility spectrum obtained at cell and injection port temperatures of 200 and 260 °C, respectively. Product ion peaks were assigned to the protonated isomers of 5-aminoindole. Density functional theory calculations were carried out to confirm the experimental results. Topical proton affinities of 5-aminoindole and dipole moments of its protonated isomers were calculated to identify the chemical structures of ions which have contributed in the creation of product ion peaks. It was shown that the combination of DFT calculations and ion mobility experiments leads to a reliable prediction of reactive protonation sites of the studied compound.