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Reaction of Arylium Ions with the Collision Gas N2 in Electrospray Ionization Mass Spectrometry



Yuxue Liang, Pedatsur Neta, Yamil Simon, Stephen E. Stein


RATIONALE: Tandem mass spectra of many compounds contained peaks which could not arise from the precursor ion and were different in different instruments. Such peaks were found to be due to reaction of arylium ions with N2 in the collision cell. Therefore, this reaction was studied in detail with representative compounds. METHODS: Various classes of compounds were dissolved in acetonitrile/water/formic acid and studied by electrospray ionization mass spectrometry to record their MS2 and pseudo-MS3 spectra in a QQQ mass spectrometer and their accurate m/z values in an Orbitrap Elite instrument. Arylium ions were found to react with N2 in the collision cell. The reaction was confirmed by MS3 studies, by comparison with authentic diazonium ions, and by the pressure dependence of the product ion survival yield. RESULTS: Reactions of arylium ions with N2 were observed with p-toluenesulfonic, o- toluenesulfonamide, phenylphosphonic acid, phenol, aniline, aminonaphthalenes, benzoic acid, benzophenone and other compounds. By using a QQQ mass spectrometer, we observed that the diazonium ion was produced with N2 but not with Ar as collision gas, and its abundance increased with increasing N2 pressure. For comparison, we examined the effect of CO2 as collision gas; it was found to react with aryl anions but not with the cations. CONCLUSIONS: Arylium ions generated from a wide range of compounds in electrospray ionization tandem mass spectrometry may react with N2 to form diazonium ions. The abundance of the diazonium ions is affected by collision energy and N2 pressure. This reaction should be considered when annotating peaks in MS/MS libraries.
Rapid Communications in Mass Spectrometry


Arylium ions, Collision gas N2, Electrospray Ionization Mass Spectrometry


Liang, Y. , Neta, P. , Simon, Y. and Stein, S. (2015), Reaction of Arylium Ions with the Collision Gas N2 in Electrospray Ionization Mass Spectrometry, Rapid Communications in Mass Spectrometry, [online], (Accessed April 13, 2024)
Created January 9, 2015, Updated November 10, 2018