Analytical improvements and assessment of long-term performance of the oxidation-denitrifier method

Simone Moretti; Nicolas N Duprey; Alan D Foreman; Anthea Arns; Sven Brömme; Jonathan Jung; Xuyuan E Ai; Alexandra Auderset; Aaron L Bieler; Camino Eck; Jesse Farmer; Barbara Hinnenberg; Matthew Lacerra; Jennifer Leichliter; Tina Lüdecke; Sergey Oleynik; Florian Rubach; Mareike Schmitt; Marissa Vink; Tanja Wald; Maayan Yehudai; Daniel M Sigman; Alfredo Martínez-García

doi:10.1002/rcm.9650

Analytical improvements and assessment of long-term performance of the oxidation-denitrifier method

Rapid Commun Mass Spectrom. 2024 Jan 15;38(1):e9650. doi: 10.1002/rcm.9650.

Authors

Simone Moretti^{1

2}, Nicolas N Duprey¹, Alan D Foreman¹, Anthea Arns¹, Sven Brömme¹, Jonathan Jung¹, Xuyuan E Ai^{1

3}, Alexandra Auderset^{1

4}, Aaron L Bieler¹, Camino Eck¹, Jesse Farmer^{1

3

5}, Barbara Hinnenberg¹, Matthew Lacerra^{1

3}, Jennifer Leichliter¹, Tina Lüdecke¹, Sergey Oleynik³, Florian Rubach¹, Mareike Schmitt¹, Marissa Vink¹, Tanja Wald¹, Maayan Yehudai¹, Daniel M Sigman³, Alfredo Martínez-García¹

Affiliations

¹ Climate Geochemistry Department, Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, Mainz, 55128, Germany.
² Istituto di Scienze Polari, Consiglio Nazionale delle Ricerche, Via Piero Gobetti 101, Bologna, 40129, Italy.
³ Department of Geosciences, Princeton University, Princeton, New Jersey, USA.
⁴ Ocean and Earth Science Programme, University of Southampton, Southampton, UK.
⁵ School for the Environment, University of Massachusetts Boston, Boston, Massachusetts, USA.

PMID: 38073197
DOI: 10.1002/rcm.9650

Abstract

The analysis of the nitrogen (N) isotopic composition of organic matter bound to fossil biomineral structures (BB-δ¹⁵ N) using the oxidation-denitrifier (O-D) method provides a novel tool to study past changes in N cycling processes.

Methods: We report a set of methodological improvements to the O-D method, including (a) a method for sealing the reaction vials in which the oxidation of organic N to NO₃ ^- takes place, (b) a recipe for bypassing the pH adjustment step before the bacterial conversion of NO₃ ^- to N₂ O, and (c) a method for storing recrystallized dipotassium peroxodisulfate (K₂ S₂ O₈ ) under Ar atmosphere.

Results: The new sealing method eliminates the occasional contamination and vial breakage that occurred previously while increasing sample throughput. The protocol for bypassing pH adjustment does not affect BB-δ¹⁵ N, and it significantly reduces the processing time. Storage of K₂ S₂ O₈ reagent under Ar atmosphere produces stable oxidation blanks over more than 3.5 years. We report analytical blanks, accuracy, and precision for this methodology from eight users over the course of ~3.5 years of analyses at the Max Planck Institute for Chemistry. Our method produces analytical blanks characterized by low N content (0.30 ± 0.13 nmol N, 1σ, n = 195) and stable δ¹⁵ N (-2.20 ± 3.13‰, n = 195). The analysis of reference amino acid standards USGS 40 and USGS 65 indicates an overall accuracy of -0.23 ± 0.35‰ (1σ, n = 891). The analysis of in-house fossil standards gives similar analytical precision (1σ) across a range of BB-δ¹⁵ N values and biominerals: zooxanthellate coral standard PO-1 (6.08 ± 0.21‰, n = 267), azooxanthellate coral standard LO-1 (10.20 ± 0.28‰, n = 258), foraminifera standard MF-1 (5.92 ± 0.28‰, n = 243), and tooth enamel AG-Lox (4.06 ± 0.49‰, n = 78).

Conclusions: The methodological improvements significantly increase sample throughput without compromising analytical precision or accuracy down to 1 nmol of N.

Abstract

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