title: On-line hydrogen-isotope measurements of organic samples using elemental chromium: an extension for high temperature elemental-analyzer techniques.
abstract: The high temperature conversion (HTC) technique using an elemental analyzer with a glassy carbon tube and filling (temperature conversion/elemental analysis, TC/EA) is a widely used method for hydrogen isotopic analysis of water and many solid and liquid organic samples with analysis by isotope-ratio mass spectrometry (IRMS). However, the TC/EA IRMS method may produce inaccurate δ(2)H results, with values deviating by more than 20 mUr (milliurey = 0.001 = 1‰) from the true value for some materials. We show that a single-oven, chromium-filled elemental analyzer coupled to an IRMS substantially improves the measurement quality and reliability for hydrogen isotopic compositions of organic substances (Cr-EA method). Hot chromium maximizes the yield of molecular hydrogen in a helium carrier gas by irreversibly and quantitatively scavenging all reactive elements except hydrogen. In contrast, under TC/EA conditions, heteroelements like nitrogen or chlorine (and other halogens) can form hydrogen cyanide (HCN) or hydrogen chloride (HCl) and this can cause isotopic fractionation. The Cr-EA technique thus expands the analytical possibilities for on-line hydrogen-isotope measurements of organic samples significantly. This method yielded reproducibility values (1-sigma) for δ(2)H measurements on water and caffeine samples of better than 1.0 and 0.5 mUr, respectively. To overcome handling problems with water as the principal calibration anchor for hydrogen isotopic measurements, we have employed an effective and simple strategy using reference waters or other liquids sealed in silver-tube segments. These crimped silver tubes can be employed in both the Cr-EA and TC/EA techniques. They simplify considerably the normalization of hydrogen-isotope measurement data to the VSMOW-SLAP (Vienna Standard Mean Ocean Water-Standard Light Antarctic Precipitation) scale, and their use improves accuracy of the data by eliminating evaporative loss and associated isotopic fractionation while handling water as a bulk sample. The calibration of organic samples, commonly having high δ(2)H values, will benefit from the availability of suitably (2)H-enriched reference waters, extending the VSMOW-SLAP scale above zero.
authors: †Department for Isotope Biogeochemistry, Helmholtz-Centre for Environmental Research (UFZ), Permoserstrasse 15, 04318 Leipzig, Germany.
authors: Matthias
authors: M
authors: Gehre
authors: †Department for Isotope Biogeochemistry, Helmholtz-Centre for Environmental Research (UFZ), Permoserstrasse 15, 04318 Leipzig, Germany.
authors: Julian
authors: J
authors: Renpenning
authors: †Department for Isotope Biogeochemistry, Helmholtz-Centre for Environmental Research (UFZ), Permoserstrasse 15, 04318 Leipzig, Germany.
authors: Tetyana
authors: T
authors: Gilevska
authors: ‡U.S. Geological Survey, 431 National Center, Reston, Virginia 20192, United States.
authors: Haiping
authors: H
authors: Qi
authors: ‡U.S. Geological Survey, 431 National Center, Reston, Virginia 20192, United States.
authors: Tyler B
authors: TB
authors: Coplen
authors: §Centre for Isotope Research (CIO), Energy and Sustainability Research Institute Groningen (ESRIG), University of Groningen, Nijenborgh 4, 9747 AG Groningen, Netherlands.
authors: Harro A J
authors: HA
authors: Meijer
authors: ∥Max-Planck-Institute for Biogeochemistry, Beutenberg Campus, P.O. Box 100164, 07701 Jena, Germany.
authors: Willi A
authors: WA
authors: Brand
authors: ⊥Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, United States.
authors: Arndt
authors: A
authors: Schimmelmann
mesh_terms: D002138:Calibration; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D002857:Chromium / Q000737:chemistry*; D004058:Diffusion; D006219:Halogens / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D007554:Isotopes; D009930:Organic Chemicals / Q000737:chemistry*; D013696:Temperature
chemical_list: D006219:Halogens; D007554:Isotopes; D009930:Organic Chemicals; D002857:Chromium; D006859:Hydrogen