[M-ZZ42] Frontiers in geochemistry: new challenges and future prospects

[MZZ42-P05] Isotopologue analysis of Polycyclic Aromatic Hydrocarbon (PAH) using Orbitrap Mass Spectrometry

*Beomsik Kim¹, Yuichiro Ueno^1,2,3 (1.Department of Earth and Planetary Sciences, Institute of Science Tokyo., 2.Earth-Life Science Institute, Institute of Science Tokyo., 3.Japan Agency for Marine-Earth Science and Technology.)

Keywords:Orbitrap Mass Spectrometry, Polycyclic Aromatic Hydrocarbon (PAH), Isotopologue, Clumped Isotope Analysis, Position Specific Isotope Analysis

Polycyclic aromatic hydrocarbons (PAHs) are widely distributed in the atmosphere, ocean, and soil. In organic geochemistry, PAHs can be extracted from sediments and/or hydropyrolysis of sedimentary organic matter, including highly matured kerogen, which can provide insights into ancient biogeochemical carbon cycling. Isotopic analysis of PAHs has been so far limited to Con-flow analyses using GC-C-IRMS systems. Here, we aim to expand the isotope analysis of PAHs to clump isotope analysis and position specific isotope analysis using an Orbitrap high-mass-resolution mass spectrometer equipped with a dual syringe system. First, for clump isotope analysis, four PAHs (anthracene, phenanthrene, pyrene, and fluoranthene) are prepared and measured their M0 (all ¹²C), M1 (single ¹³C substitution), M2 (double ¹³C substitution), M3 (triple ¹³C substitution) species separated by their precise mass. Their isotope ratios were calculated from intensity of each mass peak: ^13x1R=M1/M0, ^13x2R=M2/M0, and ^13x3R=M3/M0. And δ defined as δ^13xnC = (^13xnR_sample/^13xnR_standard-1)x1000‰. The clumped isotopologue abundance represented by the equilibrium constant of the homogeneous isotope exchange reaction, which can calculate as Δ^13x2C=δ^13x2C-2δ^13x1C and Δ^13x3C=δ^13x3C-3δ^13x1C. The dual syringe analysis of two different commercial samples of the four PAHs gave precision of 0.09~0.47‰ for δ^13x1C, and 0.06~1.27‰ for Δ^13x2C, 0.75–2.62‰ for Δ^13x3C for 17.5 nmol sample in 350 µL. Second, for position specific isotope analysis (PSIA), fragmentation of the PAH was performed using the higher-energy collisional dissociation (HCD) cell before introducing Orbitrap mass analyzer. In the case of phenanthrene (C₁₄H₁₀), C₄ to C₁₄ fragments were identified, and their carbon isotope ratios were determined. The results of HCD-Orbitrap were compared with those analyzed by ¹³C-NMR for calibration. The new high-precision PAH isotopologue analysis using Orbitrap MS may provide additional information on sedimentary organic matter to understanding the past biogeochemical carbon cycling.