Secondary processes in atmospheric pressure chemical ionization–ion trap mass spectrometry: a case study of orotic acid. Fryčák, P., Jirkovský, J., Ranc, V., Bednář, P., Havlíček, V., Lemr, K.: J. Mass Spectrom. 47, 720-726 (2012).
Atmospheric pressure chemical ionization is known for producing unusual artifacts of the ionization process in some cases. In this work, processes occuring in atmospheric pressure chemical ionization/MS of orotic acid that afforded ions accompanying protonated and deprotonated orotic acid molecules in the spectra were studied. Two processes ran in parallel in the ion source: decarboxylation of neutral orotic acid and collision-induced dissociation of its protonated or deprotonated form. A procedure discerning pre-ionization decomposition and post-ionization dissociation by manipulating ion source parameters was proposed. Experiments with isotopically labeled solvents confirmed ion-molecule reactions of the product of collision-induced dissociation of protonated orotic acid with solvent molecules in the ion source and even under vacuum in the ion trap.