Premium
Recommendations for offline combustion‐based nitrogen isotopic analysis of silicate minerals and rocks
Author(s) -
Li Long,
Li Kan,
Li Yingzhou,
Zhang Ji,
Du Yifan,
Labbe Mark
Publication year - 2021
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.9075
Subject(s) - chemistry , nitrogen , silicate , combustion , silicate minerals , isotopes of nitrogen , mineralogy , environmental chemistry , organic chemistry
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 δ 15 N 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.