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Centre for Coastal Biogeochemistry Research, Southern Cross University, Lismore 2480, NSW, Australia
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- PublicationRestrictedInterlaboratory test for stable carbon isotope analysis of dissolved inorganic carbon in geothermal fluids(2020)
; ; ; ; ; ; ; ; ; ; ; ; ; Rationale: Stable carbon isotope ratios have many applications in natural sciences. In the first worldwide interlaboratory proficiency test, the discrepancies in measured δ13CDIC values of natural waters were up to σ = ±3‰. Therefore, we continued the investigation on the analytical data quality assurance of individual laboratories and internal consistency among laboratories worldwide. Methods: We designed and performed an interlaboratory comparison exercise for δ13C analyses of ten water and two solid samples (Na2CO3, CaCO3), including two synthetic samples prepared by dissolving the carbonates individually. Three laboratories analyzed an additional sample set to assess solution stability, at least one month after the first set analysis period. The δ13C values were measured using dual inlet isotope ratio mass spectrometry (DI-IRMS) or continuous flow (CF)-IRMS. Results: The δ13C values of solid Na2CO3 and its aqueous solution were −5.06 ± 0.21‰and 5.32 ± 0.24‰, respectively, while the δ13C value of solid CaCO3 was −4.49 ± 0.93‰. Similarly, the lake water has a consistent value (2.45 ± 0.19‰). The δ13C values of geothermal water have a wide dispersion among individual laboratory measurements and among those of different laboratories; however, a trend exists in the δ13C values measured at the three sampling points of each well. Conclusions: The δ13C values of solid Na2CO3 and its solution, and lake water (i.e. DIC concentration samples >100 mg/L carbon) are consistent among all the participating laboratories. The dispersion in the δ13C values of solid CaCO3 is associated with its lower chemical affinity than that of Na2CO3. The poor reproducibility in the δ13C values of geothermal fluids, collected at three points of a geothermal well, despite overall consistent trends regarding their collection points suggests inadequate sample handling (atmospheric CO2 exchange) and/or inappropriate analytical approaches (incomplete H3PO4 acid reaction).114 4 - PublicationRestrictedStable carbon isotope analysis of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in natural waters – Results from a worldwide pro!ciency test(2013-06-21)
; ; ; ; ; ; ; ;van Geldern, R.; GeoZentrum Nordbayern, Applied Geosciences, Friedrich-Alexander-University Erlangen-Nuremberg, Schlossgarten 5, 91054 Erlangen, Germany ;Verma, M. P.; Geotermia, Instituto de Investigaciones Eléctricas, Reforma 113, Col. Palmira, Cuernavaca, Mor. C.P. 62490, Mexico ;Carvalho, M. C.; Centre for Coastal Biogeochemistry Research, Southern Cross University, Lismore 2480, NSW, Australia ;Grassa, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Delgado-Huertas, A.; Laboratorio de Biogeoquímica de Isótopos Estables, Instituto Andaluz de Ciencias de la Tierra IACT(CSIC-UGR), Avda. de las Palmeras 4, 18100 Armilla, Granada, Spain ;Monvoisin, G.; Laboratoire Interactions et Dynamiques des Environnements de Surface, Bâtiment 504, Université Paris Sud, 91405 Orsay, France ;Barth, J. A. C.; GeoZentrum Nordbayern, Applied Geosciences, Friedrich-Alexander-University Erlangen-Nuremberg, Schlossgarten 5, 91054 Erlangen, Germany; ; ; ; ; ; RATIONALE: Stable carbon isotope ratios of dissolved inorganic (DIC) and organic carbon (DOC) are of particular interest in aquatic geochemistry. The precision for this type of analysis is typically reported in the range of 0.1‰ to 0.5‰. However, there is no published attempt that compares !13C measurements of DIC and DOC among different laboratories for natural water samples. METHODS: Five natural water samples (lake water, seawater, two geothermal waters, and petroleum well water) were analyzed for !13CDIC and !13CDOC values by !ve laboratories with isotope ratio mass spectrometry (IRMS) in an international pro!ciency test. RESULTS: The reported !13CDIC values for lake water and seawater showed fairly good agreement within a range of about 1‰, whereas geothermal and petroleum waters were characterized by much larger differences (up to 6.6‰ between laboratories). !13CDOC values were only comparable for seawater and showed differences of 10 to 21‰for other samples. CONCLUSIONS: This study indicates that scatter in !13CDIC isotope data can be in the range of several per mil for samples from extreme environments (geothermal waters) and may not yield reliable information with respect to dissolved carbon (petroleum wells). The analyses of lake water and seawater also revealed a larger than expected difference and researchers from various disciplines should be aware of this. Evaluation of analytical procedures of the participating laboratories indicated that the differences cannot be explained by analytical errors or different data normalization procedures and must be related to speci!c sample characteristics or secondary effects during sample storage and handling. Our results reveal the need for further research on sources of error and on method standardization.283 41