Comprehensive inter‐laboratory calibration of reference materials for δ18O versus VSMOW using various on‐line high‐temperature conversion techniques |
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| Authors: | Willi A Brand Tyler B Coplen Anita T Aerts‐Bijma J K Böhlke Matthias Gehre Heike Geilmann Manfred Gröning Henk G Jansen Harro A J Meijer Stanley J Mroczkowski Haiping Qi Karin Soergel Hilary Stuart‐Williams Stephan M Weise Roland A Werner |
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| Institution: | 1. MPI‐BGC, Max‐Planck‐Institute for Biogeochemistry, Beutenberg Campus, P.O. Box 100164, 07701 Jena, Germany;2. USGS, U.S. Geological Survey, 431 National Center, Reston, VA 20192, USA;3. The contributions of T. B. Coplen , J. K. B?hlke and S. J. Mroczkowski to this article were prepared as part of their official duties as United States Federal Government employees.;4. CIO, Centre for Isotope Research, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands;5. UFZ, Helmholtz‐Centre for Environmental Research, Laboratory for Stable Isotopes, Permoserstrasse 15, 04318 Leipzig, Germany;6. IAEA, International Atomic Energy Agency, Isotope Hydrology Laboratory, P.O. Box 100, A‐1400 Vienna, Austria;7. ETH Zurich, Institute of Plant Sciences, Universit?tsstrasse 2, CH‐8092 Zurich, Switzerland;8. ANU, The Australian National University, Research School of Biological Sciences, Canberra, ACT 0200 Australia;9. UFZ, Helmholtz‐Centre for Environmental Research, Laboratory for Stable Isotopes, Theodor‐Lieser‐Strasse 4, 06120 Halle, Germany |
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| Abstract: | Internationally distributed organic and inorganic oxygen isotopic reference materials have been calibrated by six laboratories carrying out more than 5300 measurements using a variety of high‐temperature conversion techniques (HTC) a in an evaluation sponsored by the International Union of Pure and Applied Chemistry (IUPAC). To aid in the calibration of these reference materials, which span more than 125‰, an artificially enriched reference water (δ18O of +78.91‰) and two barium sulfates (one depleted and one enriched in 18O) were prepared and calibrated relative to VSMOW2 b and SLAP reference waters. These materials were used to calibrate the other isotopic reference materials in this study, which yielded: | Reference material | δ18O and estimated combined uncertainty c | | IAEA‐602 benzoic acid | +71.28 ± 0.36‰ | | USGS35 sodium nitrate | +56.81 ± 0.31‰ | | IAEA‐NO‐3 potassium nitrate | +25.32 ± 0.29‰ | | IAEA‐601 benzoic acid | +23.14 ± 0.19‰ | | IAEA‐SO‐5 barium sulfate | +12.13 ± 0.33‰ | | NBS 127 barium sulfate | +8.59 ± 0.26‰ | | VSMOW2 water | 0‰ | | IAEA‐600 caffeine | ?3.48 ± 0.53‰ | | IAEA‐SO‐6 barium sulfate | ?11.35 ± 0.31‰ | | USGS34 potassium nitrate | ?27.78 ± 0.37‰ | | SLAP water | ?55.5‰ | The seemingly large estimated combined uncertainties arise from differences in instrumentation and methodology and difficulty in accounting for all measurement bias. They are composed of the 3‐fold standard errors directly calculated from the measurements and provision for systematic errors discussed in this paper. A primary conclusion of this study is that nitrate samples analyzed for δ18O should be analyzed with internationally distributed isotopic nitrates, and likewise for sulfates and organics. Authors reporting relative differences of oxygen‐isotope ratios (δ18O) of nitrates, sulfates, or organic material should explicitly state in their reports the δ18O values of two or more internationally distributed nitrates (USGS34, IAEA‐NO‐3, and USGS35), sulfates (IAEA‐SO‐5, IAEA‐SO‐6, and NBS 127), or organic material (IAEA‐601 benzoic acid, IAEA‐602 benzoic acid, and IAEA‐600 caffeine), as appropriate to the material being analyzed, had these reference materials been analyzed with unknowns. This procedure ensures that readers will be able to normalize the δ18O values at a later time should it become necessary. The high‐temperature reduction technique for analyzing δ18O and δ2H is not as widely applicable as the well‐established combustion technique for carbon and nitrogen stable isotope determination. To obtain the most reliable stable isotope data, materials should be treated in an identical fashion; within the same sequence of analyses, samples should be compared with working reference materials that are as similar in nature and in isotopic composition as feasible. Copyright © 2009 John Wiley & Sons, Ltd. |
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