Preparation and characterisation of IAEA‐603, a new primary reference material aimed at the VPDB scale realisation for δ13C and δ18O determination

The stable carbon isotopic (δ 13 C) reference material (RM) LSVEC Li 2 CO 3 has been found to be unsuitable for δ 13 C standardization work because its δ 13 C value increases with exposure to atmospheric CO 2. A new CaCO 3 RM, USGS44, has been prepared to alleviate this situation. Methods: USGS44 was prepared from 8 kg of Merck high-purity CaCO 3. Two sets of δ 13 C values of USGS44 were determined. The first set of values was determined by online combustion, continuous-flow (CF) isotope-ratio mass spectrometry (IRMS) of NBS 19 CaCO 3 (δ 13 C VPDB = +1.95 milliurey (mUr) exactly, where mUr = 0.001 = 1‰), and LSVEC Li 2 CO 3 (δ 13 C VPDB = −46.6 mUr exactly), and normalized to the two-anchor δ 13 C VPDB-LSVEC isotope-delta scale. The second set of values was obtained by dual-inlet (DI)-IRMS of CO 2 evolved by reaction of H 3 PO 4 with carbonates, corrected for cross contamination, and normalized to the singleanchor δ 13 C VPDB scale. Results: USGS44 is stable and isotopically homogeneous to within 0.02 mUr in 100-μg amounts. It has a δ 13 C VPDB-LSVEC value of −42.21 ± 0.05 mUr. Single-anchor δ 13 C VPDB values of −42.08 ± 0.01 and −41.99 ± 0.02 mUr were determined by DI-IRMS with corrections for cross contamination. Conclusions: The new high-purity, well-homogenized calcium carbonate isotopic reference material USGS44 is stable and has a δ 13 C VPDB-LSVEC value of −42.21 ± 0.05 mUr for both EA/IRMS and DI-IRMS measurements. As a carbonate relatively depleted in 13 C, it is intended for daily use as a secondary isotopic reference material to normalize stable carbon isotope delta measurements to the δ 13 C VPDB-LSVEC scale. It is useful in quantifying drift with time, determining massdependent isotopic fractionation (linearity correction), and adjusting isotope-ratioscale contraction. Due to its fine grain size (smaller than 63 μm), it is not suitable as a δ 18 O reference material. A δ 13 C VPDB-LSVEC value of −29.99 ± 0.05 mUr was determined for NBS 22 oil.

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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USGS44, a new high‐purity calcium carbonate reference material for δ¹³C measurements

Moossen

Meijer

et al. 2021

“…Although it is not always necessary to abide by international certification schemes, the selection, normalization, and use of WSs should not be taken lightly. Similar to the requirements for iRMs, 7 WSs should be:…”

Section: Introductionmentioning

confidence: 99%

Designing working standards for stable H, C, and O isotope measurements in CO₂ and H₂O

Hélie

Hillaire‐Marcel

2021

Self Cite

Rationale We address here the selection, preparation, calibration, storage, and use of carbonate and water working standards (WSs) for stable H, C, and O isotope measurements requiring the best possible precision and accuracy vs international reference materials (iRMs). This may be of interest for laboratories working intensively in the domains of the carbon and water cycles and of paleoclimate. Methods Defining a WS for stable C and O isotope studies requires combining mineralogical, physical, chemical (low Mg‐ and trace‐carbonate), and isotopic measurements to select a carbonate fit for purpose; for water, two distinct deionized or distilled waters, with high and low δ2H and δ18O values, respectively, are normally used. In both cases, a strict protocol must be followed to properly qualify the WS vs the current international isotopic scales, and much attention must be paid to calculating rigorous estimates of final uncertainties on these scales. Results Two specific protocols for the selection of carbonate and water WSs are detailed. Equations for a proper estimate of uncertainties are proposed. Conclusions The selection of WSs involves a preselection of potentially suitable materials based on initial estimates of their mineralogical, chemical, and isotopic properties and long‐term stability, based on literature or previous measurements. Their precise characterization vs international isotopic scales requires a thorough analytical work in a correct sequence. When properly carried out, the proposed protocols should permit WSs to be obtained, defined vs the VSMOW and VPDB scales, with uncertainties comparable with those achieved for the characterization of iRMs.

Characterisation of new reference materials IAEA‐610, IAEA‐611 and IAEA‐612 aimed at the VPDB δ¹³C scale realisation with small uncertainty

Assonov

Fajgelj

Hélie

et al. 2021

Self Cite

Rationale LSVEC, the second anchor Reference Material (RM) for the VPDB δ13C scale realisation, was introduced in 2006. In 2015, its δ13C value was found to be drifting and, in 2017, its use as an RM for δ13C was officially discontinued by IUPAC. New RMs of low uncertainty are needed. This paper describes the preparation and characterisation of IAEA‐610, IAEA‐611 and IAEA‐612 (calcium carbonate, of chemical origin) which shall serve as a set of RMs aimed at anchoring the VPDB scale at negative δ13C values. Methods The preparation and characterisation of IAEA‐610, IAEA‐611 and IAEA‐612 were performed by addressing the contemporary technical requirements for RM production and characterisation (ISO Guide 35:2017). The three RMs were produced in large quantities, and the first batch was sealed into ampoules (0.5 g) to ensure the integrity of the RM during storage; additional batches were sealed for long‐term storage. The most accurate method of CO2 preparation and stable isotope measurements was used, namely carbonate‐H3PO4 reaction under well‐controlled conditions combined with well‐tested stable isotope ratio mass spectrometry. Results The assigned values of δ13C and associated uncertainties are based on a large number of analyses (~10 mg aliquots) performed at IAEA and address all the known uncertainty components. For aliquots down to ~100 μg, the δ13C uncertainty is increased. The uncertainty components considered are as follows: (i) material homogeneity, (ii) value assignment against IAEA‐603, (iii) potential storage effects, (iv) effect of the 17O correction, and (v) mass spectrometer linearity and cross‐contamination memory in the ion source. Conclusions The new RMs IAEA‐610, IAEA‐611 and IAEA‐612 have been characterised on the VPDB δ13C scale in a mutually consistent way. The use of three RMs will allow a consistent realisation of the VPDB δ13C scale with small uncertainty to be established, and to reach metrological compatibility of measurement results over several decades.