[M-ZZ45] Frontiers in geochemistry: discussing its appeal and future prospects

[MZZ45-05] Development of a stable isotope analysis method for methanesulfonate (MSA) using ESI-Orbitrap Mass Spectrometry

★Invited Papers

*Shohei Hattori^1,2, Yihang Hong^1,2, Longchen Zhu^1,2, Chen Yu³, Tengyu Liu³, Hao Yan^1,2, Yu Wei^1,2, Zhenfei Wang^1,2, Yongbo Peng^1,2 (1.Nanjing University, International Center for Isotope Effects Research, 2.Nanjing University, School of Earth Sciences and Engineering, 3.Nanjing University, School of Atmospheric Sciences)

Keywords:Sulfate aerosols, MSA, ESI-Orbitrap-MS, Triple oxygen isotope composition

Methanesulfonate (MSA), an oxidation product of dimethyl sulfide (DMS) originating from marine biological activities, is an oxyanion that forms a primary sulfur aerosol component in the pristine atmosphere. Earlier studies have shown that MSA possesses elevated Δ¹⁷O values, indicating that Δ¹⁷O analysis could effectively trace the atmospheric oxidation reactions of DMS (Ishino et al., 2021, JGR-A; Hattori et al., 2024, Appl. Geochem.). Nevertheless, the low atmospheric concentration of MSA and the challenges in extracting oxygen isotopic data from MSA persist. While there have been studies on sulfur isotopes (Sanusi et al. 2006), detailed analysis of the oxygen isotopic composition of MSA has been lacking.
This study presents a method for Δ¹⁷O analysis of MSA utilizing Electrospray Ionization Orbitrap Mass Spectrometry (ESI-OrbitrapMS). Direct analysis of MSA (m/z 96-98) showed that isotopologues substituted with ¹³C and ¹⁷O were indistinguishable in a high-stability low-resolution mode (60,000). However, by examining the SO₃^- fragment ions (m/z 80-82) produced via Higher-energy Collisional Dissociation (HCD), we achieved simultaneous analysis of δ³³S, δ³⁴S, δ¹⁷O, and δ¹⁸O values. Through a dual-inlet system, we developed a protocol that allows for the analysis of Δ¹⁷O values with a precision of ±1‰. This presentation will discuss calibration results using an isotopically enriched ¹⁷O standard and the determination of standard values through an offline method, thus outlining the methodology of this innovative analytical technique.