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Updated: May 19, 2026

Using a Cyclic Ion Mobility Spectrometer for Tandem Ion Mobility Experiments
Published on: January 20, 2022
Probing electrospray ionization dynamics using differential mobility spectrometry: the curious case of 4-aminobenzoic
J Larry Campbell1, J C Yves Le Blanc, Bradley B Schneider
1AB SCIEX , Concord, Ontario, Canada. larry.campbell@absciex.com
Abstract:
Here, we present the separation of two ions that differ only by the site of protonation of the analyte molecule using differential mobility spectrometry (DMS). Protonated 4-aminobenzoic acid molecules (4-ABA) generated by positive-mode electrospray ionization [ESI(+)] can exist with the proton residing on either the amine nitrogen (N-protonated) or the carboxylic acid oxygen (O-protonated), and the protonation site can differ on the basis of the solvent system used. In this study, we demonstrate the identification and separation of N- and O-protonated 4-ABA using DMS, with structural assignments verified by: (1) the presence of distinct peaks in the DMS ionogram, (2) the observed effects resulting from altering the ESI(+) solvent system, (3) the observed (13)C NMR chemical shifts arising from altering the solvent system, (4) the observation of distinct MS/MS fragmentation patterns for the two DMS-separated ions, (5) the unique hydrogen-deuterium exchange behavior for these ions, and (6) the fundamental behavior of these two ions within the DMS cell, linked back to the structural differences between the two protonated forms.
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