Chemical Ionization of Barbituric acid in Corona discharge

Ion mobility spectrometry was used for studying the chemical ionization of Barbituric acid. The ionization source was corona discharge in positive mode. Four product ion peaks were observed in the ion mobility spectrum obtained at the cell and injection port temperatures of 170 and 260 °C, respectively. Product ion peaks were assigned to the protonated isomers of Barbituric acid as fragment ions. Density functional theory calculations were carried out to confirm the experimental results. Topical proton affinities of Barbituric acid and dipole moments of its protonated isomers were calculated to identify the chemical structures of ions which have contributed to 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 probable protonation sites of the studied compound.