Recommendations for offline combustion-based nitrogen isotopic analysis of silicate minerals and rocks

• Author(s) / Creator(s)

  • Li, Long
  • Li, Kan
  • Li, Yingzhou
  • Du, Yifan
  • Labbe, Mark

• Rationale

  Due to isotope fractionations during partial nitrogen release from minerals and rocks, the complete extraction of nitrogen for analysis is crucial to ensure high-quality nitrogen isotopic data. However, the appropriate nitrogen extraction conditions (e.g. temperature, duration) have not been established for most silicate minerals and rocks.
  Methods

  Nitrogen in a number of common minerals and rocks was extracted using the most robust sealed-tube offline combustion techniques, purified and quantified in a custom-made metal manifold, and carried by helium gas to an isotope ratio mass spectrometer for isotopic measurement at nanomolar nitrogen level. Each mineral or rock was combusted in a variety of temperature and duration conditions to compare the nitrogen yields and isotopic compositions.
  Results

  The nitrogen yields and isotopic compositions of minerals and rocks are strongly affected by combustion temperature and duration. The optimal combustion temperature is lowest for cyclosilicate minerals, followed by phyllosilicate, tectosilicate and inosilicate minerals. Preheating of samples can induce significant nitrogen loss and δ15N shift. Heating of samples above their optimal temperatures may cause nitrogen re-assimilation by the residual mineral or rock.
  Conclusions

  Each mineral or rock has a characteristic optimal temperature and duration for complete nitrogen release. Preheating, under-heating or over-heating can cause nitrogen loss and isotopic shift. Therefore, we recommend using the offline combustion techniques and the optimal combustion conditions obtained in this study for nitrogen quantification and isotopic analysis of silicate minerals and rocks.

• Date created

  2021-03-01

• Subjects / Keywords

  • Nitrogen isotopes
  • Offline combustion
  • Combustion temperature
  • Minerals
  • Rocks

• Type of Item

  Article (Draft / Submitted)

• DOI

  https://doi.org/10.7939/r3-ggss-6316

• License

  This is the peer reviewed version of the following article: Li, L., Li, K., Li, Y., Zhang, J., Du, Y., & Labbe, M. (2021). Recommendations for offline combustion-based nitrogen isotopic analysis of silicate minerals and rocks. RAPID COMMUNICATIONS IN MASS SPECTROMETRY, 35(10), e9075., which has been published in final form at https://doi.org/10.1002/rcm.9075. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.