Assessing the Blank Carbon Contribution, Isotope Mass Balance, and Kinetic Isotope Fractionation of the Ramped Pyrolysis/Oxidation Instrument at NOSAMS Academic Article uri icon

abstract

  • Abstract We estimate the blank carbon mass over the course of a typical Ramped PyrOx (RPO) analysis (150–1000°C; 5°C×min–1) to be (3.7±0.6) ?g C with an Fm value of 0.555±0.042 and a ?13C value of (–29.0±0.1) ‰ VPDB. Additionally, we provide equations for RPO Fm and ?13C blank corrections, including associated error propagation. By comparing RPO mass-weighted mean and independently measured bulk ?13C values for a compilation of environmental samples and standard reference materials (SRMs), we observe a small yet consistent 13C depletion within the RPO instrument (mean–bulk: ?=–0.8‰; ±1?=0.9‰; n=66). In contrast, because they are fractionation-corrected by definition, mass-weighted mean Fm values accurately match bulk measurements (mean–bulk: ?=0.005; ±1?=0.014; n=36). Lastly, we show there exists no significant intra-sample ?13C variability across carbonate SRM peaks, indicating minimal mass-dependent kinetic isotope fractionation during RPO analysis. These data are best explained by a difference in activation energy between 13C- and 12C-containing compounds (13–12 ?E) of 0.3–1.8 J×mol–1, indicating that blank and mass-balance corrected RPO ?13C values accurately retain carbon source isotope signals to within 1–2‰.
  • AbstractWe estimate the blank carbon mass over the course of a typical Ramped PyrOx (RPO) analysis (150–1000°C; 5°C×min–1) to be (3.7±0.6) ?g C with an Fm value of 0.555±0.042 and a ?13C value of (–29.0±0.1) ‰ VPDB. Additionally, we provide equations for RPO Fm and ?13C blank corrections, including associated error propagation. By comparing RPO mass-weighted mean and independently measured bulk ?13C values for a compilation of environmental samples and standard reference materials (SRMs), we observe a small yet consistent 13C depletion within the RPO instrument (mean–bulk: ?=–0.8‰; ±1?=0.9‰; n=66). In contrast, because they are fractionation-corrected by definition, mass-weighted mean Fm values accurately match bulk measurements (mean–bulk: ?=0.005; ±1?=0.014; n=36). Lastly, we show there exists no significant intra-sample ?13C variability across carbonate SRM peaks, indicating minimal mass-dependent kinetic isotope fractionation during RPO analysis. These data are best explained by a difference in activation energy between 13C- and 12C-containing compounds (13–12?E) of 0.3–1.8 J×mol–1, indicating that blank and mass-balance corrected RPO ?13C values accurately retain carbon source isotope signals to within 1–2‰.

publication date

  • February 2017