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How Soft Is Secondary Electrospray Ionization?
Jérôme Kaeslin1, Cedric Wüthrich1, Stamatios Giannoukos1
1Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland.
Journal of the American Society for Mass Spectrometry
|September 16, 2022
Summary
Secondary electrospray ionization (SESI) mass spectrometry is a soft ionization technique. However, standard instrument settings are harsh; soft tuning is essential for optimal performance in metabolomics and breath analysis.
Area of Science:
- Analytical Chemistry
- Physical Chemistry
Background:
- Secondary electrospray ionization (SESI) mass spectrometry (MS) is a direct infusion technique used for untargeted metabolomics, particularly in online breath analysis.
- SESI is considered a soft ionization method, crucial for minimizing in-source fragments and simplifying compound annotation.
Purpose of the Study:
- To investigate the internal energy distribution of ions produced by SESI.
- To evaluate SESI's softness compared to electrospray ionization (ESI) and assess the impact of instrument settings.
Main Methods:
- Utilized benzylammonium ions as thermometer ions with known bond dissociation enthalpies.
- Employed in-source collision-induced dissociation (CID) experiments.
Main Results:
- Demonstrated that SESI is softer than ESI.
- Revealed that standard MS instrument settings in SESI are often too harsh for optimal soft ionization.
- Provided evidence for analyte solvation under soft SESI conditions, supporting the ligand switching mechanism.
Conclusions:
- SESI qualifies as a soft ionization technique, but requires proper instrument tuning to leverage its full potential.
- Optimized SESI conditions are critical for accurate metabolomics and breath analysis.
- Findings support the ligand switching mechanism in SESI.
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