Nitrogen abundance and isotope analysis of silicate glasses by secondary ionization mass spectrometry

Redox control on nitrogen isotope fractionation during planetary core formation

“…The N contents of silicate glasses in each sample were homogeneous with a SD below 9%. As observed by Dalou et al (17) and Füri et al (40), the glasses contained micrometer-sized graphite inclusions, causing highly variable C signals over the course of an analysis and between distinct areas. Given that silicate glass N contents and isotopic compositions were measured as 14 N 16 O − / 16 O 2 − and 15 N 16 O − / 14 N 16 O − instead of 12 C 14 N − / 12 C 2 − and 12 C 15 N − / 12 C 14 N − , this variability does not affect our N-elemental and -isotopic analyses (40).…”

“…As observed by Dalou et al (17) and Füri et al (40), the glasses contained micrometer-sized graphite inclusions, causing highly variable C signals over the course of an analysis and between distinct areas. Given that silicate glass N contents and isotopic compositions were measured as 14 N 16 O − / 16 O 2 − and 15 N 16 O − / 14 N 16 O − instead of 12 C 14 N − / 12 C 2 − and 12 C 15 N − / 12 C 14 N − , this variability does not affect our N-elemental and -isotopic analyses (40). In samples for which metal blobs were large enough to perform multiple measurements (up to 4 analyses in HB05 and HB3, and 6 in HB4), homogeneous N-isotopic ratios were observed across the metal blobs, with SDs below 2% (2σ; SI Appendix , Table S3).…”

“…We thus developed a method for in situ measurement of the N concentrations and isotopic compositions of quenched silicate and metal alloy phases by secondary ion mass spectrometry (SIMS) using the CAMECA IMS 1280 HR2 and 1270 at the Centre de Recherches Pétrographiques et Géochimiques (Nancy, France). Following the analytical protocol of Füri et al (40), nitrogen isotopes in silicate glasses were measured with the IMS 1280 HR2 by spot analyses of 14 N 16 O − and 15 N 16 O − secondary molecular ions at mass numbers 30 and 31, respectively, at a nominal mass resolution m /Δ m = 14,000 using a Cs + primary ion beam with a current of ∼10 nA. A suite of reference glasses with known 14 N contents (40, 41) was used to determine the nitrogen concentration of each sample based on the 14 N 16 O − count rate normalized by the 16 O 2 – signal ( SI Appendix , section S1).…”

“…Following the analytical protocol of Füri et al (40), nitrogen isotopes in silicate glasses were measured with the IMS 1280 HR2 by spot analyses of 14 N 16 O − and 15 N 16 O − secondary molecular ions at mass numbers 30 and 31, respectively, at a nominal mass resolution m /Δ m = 14,000 using a Cs + primary ion beam with a current of ∼10 nA. A suite of reference glasses with known 14 N contents (40, 41) was used to determine the nitrogen concentration of each sample based on the 14 N 16 O − count rate normalized by the 16 O 2 – signal ( SI Appendix , section S1). The nitrogen and carbon abundances and 15 N/ 14 N and 13 C/ 12 C ratios of metal phases were measured on the IMS 1270 using a Cs + primary ion beam with a current of ∼2.4 nA.…”

“…Owing to the low Si solubility in metals at the studied pressure–temperature ( P–T ) and f O 2 conditions (17), 28 Si − was analyzed to monitor for potential silicate contamination during analyses. In parallel to the SIMS measurements, the nitrogen contents and 15 N/ 14 N ratios of reference silicate glasses (40) and metal reference materials were determined independently by noble gas mass spectrometry ( SI Appendix , section S1). The use of 15 N-spiked samples allowed us to determine the 15 N/ 14 N ratios in the silicate and metal phases with average analytical uncertainties of 0.1‰ and 5.5‰, respectively.…”