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 WaldMaayan Yehudai, Daniel M. Sigman, Alfredo Martínez-García

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The analysis of the nitrogen (N) isotopic composition of organic matter bound to fossil biomineral structures (BB-δ15N) 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 N2O, and (c) a method for storing recrystallized dipotassium peroxodisulfate (K2S2O8) 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-δ15N, and it significantly reduces the processing time. Storage of K2S2O8 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 δ15N (−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-δ15N 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.

Original languageEnglish (US)
Article numbere9650
JournalRapid Communications in Mass Spectrometry
Issue number1
StatePublished - Jan 15 2024

All Science Journal Classification (ASJC) codes

  • Analytical Chemistry
  • Spectroscopy
  • Organic Chemistry


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