Gábor Újvári1,2, Urs Klötzli1, Monika Horschinegg1, Wencke Wegner3, Dorothee Hippler4, Gabriella Ilona Kiss5, László Palcsu5. 1. Department of Lithospheric Research, University of Vienna, Vienna, 1090, Austria. 2. Institute for Geological and Geochemical Research, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Budapest, 1112, Hungary. 3. Natural History Museum, Vienna, 1010, Austria. 4. Institute of Applied Geosciences, Graz University of Technology, Graz, 8010, Austria. 5. Isotope Climatology and Environmental Research Centre, Institute for Nuclear Research, Debrecen, 4026, Hungary.
Abstract
RATIONALE: Complete decomposition of silicate rock matrices is crucial in determining their isotopic compositions, but acid dissolution in a high-pressure steel-jacketed bomb, which has been the only powerful, effective technique thus far, is time-consuming and expensive. Rock dissolution using ammonium bifluoride (ABF), as described here, is a viable alternative. METHODS: Geological reference materials (GRMs) were digested using ABF in closed Teflon beakers at temperatures of 220/230°C in a convection oven and subsequently treated with HNO3 . Hf-Sr-Nd were separated and purified using ion-exchange chemistry columns calibrated for 50-2 mg samples. The isotopic compositions of Sr-Nd were measured by Thermal Ionization Mass Spectrometry, while that of Hf by Multi-Collector Inductively Coupled Plasma Mass Spectrometry, both with normal 1011 Ω and gain calibrated 1013 Ω amplifiers. RESULTS: Total procedural blanks of our protocol are 0.5 ng for Sr, 0.2 ng for Nd and <25 pg for Hf. Test runs with GRMs, ranging in composition from basic to felsic and dissolved in ABF, yield accurate 87 Sr/86 Sr, 143 Nd/144 Nd and 176 Hf/177 Hf isotope ratios as compared with those obtained with the bomb dissolution technique. Reproducibilities were comparable, on the order of 10-20 ppm. Our technique allows combined Hf-Sr-Nd isotope analyses of low-mass (50-2 mg) samples. CONCLUSIONS: The ABF digestion is an alternative technique to high-pressure bomb dissolution in matrix decomposition for accurate and reproducible Hf-Nd-Sr isotope analyses of geological samples within a reasonable time (3-4 days), with high sample throughput and low costs in geochemistry and environmental sciences.
RATIONALE: Complete decomposition of silicate rock matrices is crucial in determining their isotopic compositions, but acid dissolution in a high-pressure steel-jacketed bomb, which has been the only powerful, effective technique thus far, is time-consuming and expensive. Rock dissolution using ammonium bifluoride (ABF), as described here, is a viable alternative. METHODS: Geological reference materials (GRMs) were digested using ABF in closed Teflon beakers at temperatures of 220/230°C in a convection oven and subsequently treated with HNO3 . Hf-Sr-Nd were separated and purified using ion-exchange chemistry columns calibrated for 50-2 mg samples. The isotopic compositions of Sr-Nd were measured by Thermal Ionization Mass Spectrometry, while that of Hf by Multi-Collector Inductively Coupled Plasma Mass Spectrometry, both with normal 1011 Ω and gain calibrated 1013 Ω amplifiers. RESULTS: Total procedural blanks of our protocol are 0.5 ng for Sr, 0.2 ng for Nd and <25 pg for Hf. Test runs with GRMs, ranging in composition from basic to felsic and dissolved in ABF, yield accurate 87 Sr/86 Sr, 143 Nd/144 Nd and 176 Hf/177 Hf isotope ratios as compared with those obtained with the bomb dissolution technique. Reproducibilities were comparable, on the order of 10-20 ppm. Our technique allows combined Hf-Sr-Nd isotope analyses of low-mass (50-2 mg) samples. CONCLUSIONS: The ABF digestion is an alternative technique to high-pressure bomb dissolution in matrix decomposition for accurate and reproducible Hf-Nd-Sr isotope analyses of geological samples within a reasonable time (3-4 days), with high sample throughput and low costs in geochemistry and environmental sciences.
Authors: G Újvári; U Klötzli; T Stevens; A Svensson; P Ludwig; T Vennemann; S Gier; M Horschinegg; L Palcsu; D Hippler; J Kovács; C Di Biagio; P Formenti Journal: J Geophys Res Atmos Date: 2022-08-05 Impact factor: 5.217