David X Soto1,2, Geoff Koehler1, Leonard I Wassenaar1,3, Keith A Hobson1,4. 1. Environment and Climate Change Canada, 11 Innovation Boulevard, Saskatoon, SK, Canada. 2. Department of Earth and Environmental Sciences, KU Leuven, B-3001, Leuven, Belgium. 3. International Atomic Energy Agency, Vienna, Austria. 4. Department of Biology, University of Western Ontario, London, ON, Canada.
Abstract
RATIONALE: Determination of non-exchangeable hydrogen isotopic compositions (δ2 H values) of bulk complex organic materials is difficult due to uncontrolled H isotope exchange between the organic material and ambient water vapor. A number of calibration keratinous materials with carefully measured hydrogen isotopic compositions of the non-exchangeable fraction were proposed to enable stable isotope laboratories to normalize their 2 H measurements. However, it was recently reported that high-temperature carbon-reactor methods for measuring the hydrogen isotopic composition of nitrogenous organic materials is biased by the production of HCN in the reactor. As a result, the reported values of these calibration materials needed to be re-evaluated. METHODS: We evaluated the non-exchangeable δ2 HVSMOW values of keratins EC1 (CBS) and EC2 (KHS), USGS hair standards, and a range of other nitrogenous widely used organic laboratory calibration materials (collagen and chitin) using pre-treatment with a preparation device designed to eliminate residual moisture and quantify exchangeable H. RESULTS: The revised non-exchangeable δ2 HVSMOW values of EC-1 (CBS) and EC-2 (KHS) keratin standard materials were -157.0 ± 0.9 and -35.3 ± 1.1 ‰, respectively. The revised values of USGS42 and USGS43 were -72.2 ± 0.9 and -44.2 ± 1.0 ‰, respectively, in excellent agreement with previous results. CONCLUSIONS: For routine H isotope analyses, with proper sample pre-treatment, we show that the Comparative Equilibration approach can provide accurate and reproducible non-exchangeable δ2 H values among laboratories regardless of the reactor type used.
RATIONALE: Determination of non-exchangeable hydrogen isotopic compositions (δ2 H values) of bulk complex organic materials is difficult due to uncontrolled H isotope exchange between the organic material and ambient water vapor. A number of calibration keratinous materials with carefully measured hydrogen isotopic compositions of the non-exchangeable fraction were proposed to enable stable isotope laboratories to normalize their 2 H measurements. However, it was recently reported that high-temperature carbon-reactor methods for measuring the hydrogen isotopic composition of nitrogenous organic materials is biased by the production of HCN in the reactor. As a result, the reported values of these calibration materials needed to be re-evaluated. METHODS: We evaluated the non-exchangeable δ2 HVSMOW values of keratins EC1 (CBS) and EC2 (KHS), USGS hair standards, and a range of other nitrogenous widely used organic laboratory calibration materials (collagen and chitin) using pre-treatment with a preparation device designed to eliminate residual moisture and quantify exchangeable H. RESULTS: The revised non-exchangeable δ2 HVSMOW values of EC-1 (CBS) and EC-2 (KHS) keratin standard materials were -157.0 ± 0.9 and -35.3 ± 1.1 ‰, respectively. The revised values of USGS42 and USGS43 were -72.2 ± 0.9 and -44.2 ± 1.0 ‰, respectively, in excellent agreement with previous results. CONCLUSIONS: For routine H isotope analyses, with proper sample pre-treatment, we show that the Comparative Equilibration approach can provide accurate and reproducible non-exchangeable δ2 H values among laboratories regardless of the reactor type used.
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