ArticleJournal of the American Society for Mass Spectrometry2025
Unlocking PAH Ionization in Negative-Mode ESI Orbitrap MS Using Tetramethylammonium Hydroxide: A Petroleomic Strategy.
Article in Journal of the American Society for Mass Spectrometry, 2025. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
The selective ionization of cyclopentadiene-derived polycyclic aromatic hydrocarbons (PAHs) in complex matrices remains a persistent challenge in direct ionization mass spectrometry, particularly under atmospheric pressure ionization (API) conditions. In this study, tetramethylammonium hydroxide (TMAH) was evaluated as a solvent modifier to enhance the ionization efficiency of PAHs in negative-ion mode using high-resolution Orbitrap MS. A systematic assessment with equimolar mixtures of neutral and acidic model compounds was performed to elucidate the fundamental effects of TMAH on ion suppression, deprotonation mechanisms, and gas-phase ion chemistry. The incorporation of TMAH significantly improved the detection of weakly acidic and neutral PAHs by promoting efficient gas-phase deprotonation, thus overcoming conventional ESI limitations. To demonstrate the method's analytical robustness, TMAH-assisted ESI was subsequently applied to crude oil samples, enabling the detection of hydrocarbon species otherwise inaccessible under standard conditions, with a particular focus on low-alkylated fluorene derivatives. These results establish a simple and effective strategy for expanding the analytical scope of ESI-MS toward nonpolar and weakly acidic hydrocarbons, offering a valuable tool for the advanced molecular characterization of complex organic mixtures.
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