Assessing the blank carbon contribution, isotope mass balance, and kinetic isotope fractionation of the Ramped Pyrolysis/Oxidation instrument at NOSAMS
Assessing the blank carbon contribution, isotope mass balance, and kinetic isotope fractionation of the Ramped Pyrolysis/Oxidation instrument at NOSAMS
Date
2017-03
Authors
Hemingway, Jordon D.
Galy, Valier
Gagnon, Alan R.
Grant, Katherine E.
Rosengard, Sarah Z.
Soulet, Guillaume
Zigah, Prosper
McNichol, Ann P.
Galy, Valier
Gagnon, Alan R.
Grant, Katherine E.
Rosengard, Sarah Z.
Soulet, Guillaume
Zigah, Prosper
McNichol, Ann P.
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Abstract
We estimate the blank carbon mass over the course of a typical Ramped PyrOx (RPO)
analysis (150 to 1000 °C; 5 °C×min-1) to be (3.7 ± 0.6) μg C with an Fm value of 0.555 ± 0.042
and a δ13C value of (-29.0 ± 0.1) ‰ VPDB. Additionally, we provide equations for RPO Fm and
δ13C blank corrections, including associated error propagation. By comparing RPO mass-weighted mean and independently measured bulk δ13C 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: μ = -0.8 ‰; ±1σ = 0.9 ‰; n = 66). In
contrast, because they are fractionation-corrected by definition, mass-weighted mean Fm values
accurately match bulk measurements (mean – bulk: μ = 0.005; ±1σ = 0.014; n = 36). Lastly, we
show there exists no significant intra-sample δ13C 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 (13–12ΔE) of 0.3 to 1.8 J×mol-1, indicating that blank and mass-balance corrected
RPO δ13C values accurately retain carbon source isotope signals to within 1 to 2‰.
Description
Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Radiocarbon 59 (2017): 179-193, doi:10.1017/RDC.2017.3.