Determination of stable carbon isotope ratios for molecules in natural organic matter using ESI FT-ICR MS.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 42308308.
- Also identified by DOI 10.1126/sciadv.aee5238 and PMC identifier 13274584.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
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 (Δδ<sup>13</sup>C) across samples. Between terrestrial and marine NOM, we observed Δδ<sup>13</sup>C values of 17.3, 8.8, and 10.1‰ for marine-enriched formulas C<sub>19</sub>H<sub>22</sub>O<sub>10</sub>, C<sub>20</sub>H<sub>26</sub>O<sub>9</sub>, and C<sub>20</sub>H<sub>24</sub>O<sub>9</sub>, respectively, whereas an invariant formula, C<sub>18</sub>H<sub>22</sub>O<sub>6</sub>, showed a nonsignificant difference (Δδ<sup>13</sup>C = 2.7‰, <i>P</i> = 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 δ<sup>13</sup>C values were obtained, e.g., -46.8‰ for C<sub>18</sub>H<sub>22</sub>O<sub>6</sub> in terrestrial NOM.