title: Bulk δ15N measurements of organic-rich rock samples by elemental analyzer/isotope ratio mass spectrometry with enhanced oxidation ability.
abstract: BACKGROUND
  Elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) has been widely used for nitrogen isotope ratio determination in various organic and inorganic samples. However, the extent of the redox reaction in the EA reaction tube can greatly affect the accuracy and precision of measurements, especially in the case of complex geological samples. It is therefore necessary to determine the appropriate reaction conditions to reach a high recovery of nitrogen by complete combustion or thermal decomposition and quantitative reduction.
  
  
  METHODS
  The conventional Dumas dual-inlet method was used to determine the bulk nitrogen isotope composition of SGR-1 (an organic-rich standard sample), which then was analyzed by EA/IRMS under different EA reaction conditions to study the influence of the redox environment on the δ15N measurements. The measured data together with the results reported by previous researchers were used to evaluate the effectiveness of the nitrogen extraction for organic-rich rock samples.
  
  
  RESULTS
  Our results demonstrated that with the Dumas dual-inlet method more oxidizing agent (CuO) addition to SGR-1 would yield a higher nitrogen content of 0.91% than the recommended content (0.81%) although a δ15N value of 17.39 ± 0.09‰ was consistent with the recommended value by USGS. Using EA/IRMS, when more O2was injected in the reaction tube, a high nitrogen content (0.92 ± 0.01%) and a δ15N value (17.43 ± 0.17‰) close to that of the Dumas dual-inlet method were obtained. The addition of V2O5or CuO in a continuous-flow system of EA/IRMS could not effectively enable the complete combustion of SGR-1.
  
  
  CONCLUSIONS
  When measuring the nitrogen isotope composition of organic-rich rock sample dominated by reduced substances with EA/IRMS, greater O2injection will enable more complete combustion to obtain reliable nitrogen yields compared with the addition of V2O5or CuO. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Institute of Geology and Geophysics, Chinese Academy of Sciences, PO Box 9825, Beijing, 100029, China.
authors.forename: Wennian
authors.initials: W
authors.lastname: Han
authors.affiliation: Institute of Geology and Geophysics, Chinese Academy of Sciences, PO Box 9825, Beijing, 100029, China.
authors.forename: Lianjun
authors.initials: L
authors.lastname: Feng
authors.affiliation: Institute of Geology and Geophysics, Chinese Academy of Sciences, PO Box 9825, Beijing, 100029, China.
authors.forename: Hongwei
authors.initials: H
authors.lastname: Li
authors.affiliation: Institute of Geology and Geophysics, Chinese Academy of Sciences, PO Box 9825, Beijing, 100029, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Liu