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Updated: Feb 6, 2026

Sample Preparation for Probe Electrospray Ionization Mass Spectrometry
Published on: February 19, 2020
Probing the Structures of Solvent-Complexed Ions Formed in Electrospray Ionization Using Cryogenic Infrared
Matthew R Bell1, Vinícius Wilian D Cruzeiro1, Adam P Cismesia1
1Department of Chemistry , University of Florida , P.O. Box 117200, Gainesville , Florida 32611-7200 , United States.
Abstract:
The gas-phase infrared photodissociation (IRPD) spectra of solvent-tagged small biomolecules are studied in a cryogenic ion trap at 17 K. In this study para-aminobenzoic acid (PABA) and tyramine molecules are noncovalently tagged with water or acetonitrile in the electrospray ionization (ESI) source. The complexes are then cooled in the cryogenic trap prior to spectroscopic measurements. These molecules provide two putative sites for solvent attachment: the protonated amine (NH3+) and the OH groups. Comparisons of the experimental IR spectra to theoretical spectra obtained with density functional theory show that the NH3+ site is mainly favored. Evidence for the formation of both NH3-bound and OH-bound conformers is found only in tyramine, despite having similar solution- and gas-phase energetics to that of PABA. Since the structures cannot interconvert in the gas phase, this suggests an isomerization during the electrospray process.
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