Acetonitrile Ion Suppression in Atmospheric Pressure Ionization Mass Spectrometry
Date of Original Version
Efforts to analyze trace levels of cyclic peroxides by liquid chromatography/mass spectrometry gave evidence that acetonitrile suppressed ion formation. Further investigations extended this discovery to ketones, linear peroxides, esters, and possibly many other types of compounds, including triazole and menadione. Direct ionization suppression caused by acetonitrile was observed for multiple adduct types in both electrospray ionization and atmospheric pressure chemical ionization. The addition of only 2% acetonitrile significantly decreased the sensitivity of analyte response. Efforts to identify the mechanism were made using various nitriles. The ion suppression was reduced by substitution of an acetonitrile hydrogen with an electron-withdrawing group, but was exacerbated by electron-donating or steric groups adjacent to the nitrile. Although current theory does not explain this phenomenon, we propose that polar interactions between the various functionalities and the nitrile may be forming neutral aggregates that manifest as ionization suppression. [Figure not available: see fulltext.]
Journal of the American Society for Mass Spectrometry
Colizza, Kevin, Keira E. Mahoney, Alexander V. Yevdokimov, James L. Smith, and Jimmie C. Oxley. "Acetonitrile Ion Suppression in Atmospheric Pressure Ionization Mass Spectrometry." Journal of the American Society for Mass Spectrometry 27, 11 (2016): 1796-1804. doi:10.1007/s13361-016-1466-1.