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Issue 2, 2013
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Effect of ammonium on liquid- and gas-phase protonation and deprotonation in electrospray ionization mass spectrometry

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Abstract

The electrospray ionization (ESI) is a complex process and there has been a long debate regarding the gas-phase effect on ion generation in the process. In this paper we investigated the effect of liquid chromatographic mobile phase additives (formic acid, aqueous ammonia and their combination) on the ESI signal intensities for a wide variety of compounds. The addition of a trace amount of aqueous ammonia to the common formic acid–methanol mobile phase significantly enhances the ESI signals of protonated molecules and suppresses the formation of sodium adduct ions. This effect is well observed for the compounds containing the –N–C[double bond, length as m-dash]O group but not for those without N or O atoms. The ESI signal intensity of deprotonated molecules increases with increase in pH of the mobile phase for neutral compounds, such as substituted urea, whereas this trend is not observed for acidic compounds such as phenoxy acids. The mechanistic analysis regarding liquid- and gas-phase protonation and deprotonation is discussed.

Graphical abstract: Effect of ammonium on liquid- and gas-phase protonation and deprotonation in electrospray ionization mass spectrometry

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Supplementary files

Article information


Submitted
05 Aug 2011
Accepted
13 Nov 2012
First published
26 Nov 2012

Analyst, 2013,138, 659-665
Article type
Paper

Effect of ammonium on liquid- and gas-phase protonation and deprotonation in electrospray ionization mass spectrometry

X. J. Yang, Y. Qu, Q. Yuan, P. Wan, Z. Du, D. Chen and C. Wong, Analyst, 2013, 138, 659
DOI: 10.1039/C2AN36022E

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