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Updated: Jun 19, 2026

Sampling and Pretreatment of Tooth Enamel Carbonate for Stable Carbon and Oxygen Isotope Analysis
Published on: August 15, 2018
Determination of stable carbon isotope ratios for molecules in natural organic matter using ESI FT-ICR MS
Shuxian Gao1, Boris P Koch2,3, Steffen Kümmel4
1Department Environmental Analytical Chemistry, Research Group BioGeoOmics, Helmholtz Centre for Environmental Research-UFZ, Permoserstr. 15, Leipzig D-04318, Germany.
Abstract:
Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) enables nontargeted identification of molecular formulas in natural organic matter (NOM), yet molecular-level isotope analysis at natural abundance remains limited. Here, we present a comprehensive workflow for molecular formula-specific isotope analysis (MSIA) in NOM using FT-ICR MS, including calibration against universal reference materials (RMs). The central step of MSIA is an intensity-tuning strategy that, with sufficient spectral averaging, achieves sub-per mil (‰) precision and accuracy and enables robust isotopic comparison (Δδ13C) across samples. Between terrestrial and marine NOM, we observed Δδ13C values of 17.3, 8.8, and 10.1‰ for marine-enriched formulas C19H22O10, C20H26O9, and C20H24O9, respectively, whereas an invariant formula, C18H22O6, showed a nonsignificant difference (Δδ13C = 2.7‰, P = 0.296). Matrix effects for RMs spiked into NOM were within the method uncertainty, rendering existing RMs suitable for MSIA when matched in carbon number, peak intensity, and mass (<50 daltons). Under these conditions, molecular formula-level δ13C values were obtained, e.g., -46.8‰ for C18H22O6 in terrestrial NOM.
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