Preparation and characterisation of IAEA-603, a new primary reference material aimed at the VPDB scale realisation for δ13 C and δ18 O determination

RATIONALE

NBS19 carbonate, a primary reference material (RM) for the Vienna Pee Dee Belemnite (VPDB) scale realisation introduced in 1987, was exhausted in 2009, and no primary RM was available for several years. This study describes the preparation and characterisation of a new RM, IAEA-603 (Ca-carbonate, calcite of marble origin), which shall serve as a new primary RM (replacement for NBS19) or primary calibrator aimed at the highest realisation of the VPDB scale for δ¹³ C and δ¹⁸ O values, including the VPDB-CO₂ δ¹⁸ O scale.

METHODS

IAEA-603 preparation and characterisation (value transfer) against NBS19 were performed by addressing the major modern technical requirements for the production and characterisation of RMs (ISO Guide 35). IAEA-603 was produced in a large quantity, and the first batch was sealed into ampoules (0.5 g) to ensure RM integrity during storage; four other batches were sealed for long-term storage. The most accurate method of CO₂ preparation for isotope mass spectrometry was used, namely carbonate-H₃ PO₄ reaction under controlled conditions.

RESULTS

The assigned values of δ¹³ C = +2.460 ± 0.010‰ and δ¹⁸ O = -2.370 ± 0.040‰ (k = 1) 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 120 μg, the δ¹⁸ O uncertainty remains unchanged but shall be doubled for δ¹³ C. The uncertainty components considered are as follows: (a) material homogeneity (within and between the 5200 ampoules produced), (b) value assignment against NBS19, (c) storage effects and (d) effect of the ¹⁷ O correction.

CONCLUSIONS

The new primary RM IAEA-603 replaces NBS19 in its use as the highest calibrator for the VPDB δ¹³ C and δ¹⁸ O scale, including the VPDB-CO₂ δ¹⁸ O scale. The use of IAEA-603 will allow laboratories worldwide to establish consistent realisation of the scales for δ¹³ C and δ¹⁸ O values and metrological comparability of measurement results for decades. The VPDB scale definition based on NBS19 stays valid.

USE OF Tc-99m-PERTECHNETATE TO FOLLOW LIQUID WATER UPTAKE BY PORCELLIO SCABER

Terrestrial isopods are, apart from the amphipods, the only group of crustaceans living on land. They have evolved some functional and anatomical adaptations to manage water and ion exchange between themselves and their environment, and these are different from those in all other crustaceans. In higher terrestrial isopods, liquid water is taken in by mouth (Hoese, 1981) and water vapour is absorbed in the pleoventral space (Wright and Machin, 1990; Wright and O'Donnell, 1992). Spencer and Edney (1954) also showed that water from wet filter paper can be taken up by the animals' rear appendages (uropods).

Matrix materials for proficiency testing: optimization of a procedure for spiking soil with gamma-emitting radionuclides

The IAEA Reference Materials Group of the Chemistry Unit, Agency's Laboratories Seibersdorf, has developed and optimized a procedure for spiking some environmental matrices with gamma-emitting radionuclides. This paper describes the spiking procedure, homogeneity testing of the spiked material, and assignment of property values and their associated uncertainties for the radionuclides 54Mn, 65Zn, 60Co, 109Cd, 134Cs, 137Cs, 210Pb, and 241Am. This procedure has already been successfully used in an IAEA proficiency test on the determination of 137Cs and 210Pb in spiked soil and has been found to be appropriate for production of soil materials for proficiency testing and internal quality control samples. The main advantage of this procedure is a low uncertainty arising from heterogeneity, which was found to be less than 1.2% for all the analytes studied.

On the metrological traceability and hierarchy of stable isotope reference materials aimed at realisation of the VPDB scale: Revision of the VPDB δ13 C scale based on multipoint scale-anchoring RMs

RATIONALE

In recent years, the primary reference material (RM) for the VPDB scale, NBS19, has become unavailable, and the RM used for low-end scale-anchoring, LSVEC, was found unsuitable due a drift in the δ¹³ C value. Given these problems, new RMs aimed at realising the VPDB δ¹³ C scale with low uncertainty were produced. Establishing the consistency of the new RMs with the "old" RMs prompted our revision of the underlying principles of RM value assignments, and the VPDB δ¹³ C scale realisation and its long-term sustainability.

METHODS

Analysis of major developments of the VPDB scale, a review of the contemporary requirements for RMs, and comparison with well-established measurement scales have been performed, with the aim of revising the VPDB δ¹³ C scale, principles of RM value assignments, and calibrator hierarchy. Requirements for scale-anchoring RMs with low uncertainty and measures to establish the scale sustainability have been formulated.

RESULTS

The revised scale realisation is based on multiple reference points, well-defined calibration hierarchy and the use of well-understood methods for value assignment. The realisation scheme includes the new primary RM IAEA-603 and scale-anchoring RMs IAEA-610, IAEA-611 and IAEA-612, covering δ¹³ C from +2.46 to -36.7 ‰ VPDB, with uncertainties, including inhomogeneity and stability assessment, of less than 0.015 ‰. The values of these four RMs were assigned in a mutually consistent way; agreement between measurements made using this realisation with those made using the VPDB scale of 2006 has been demonstrated on NIST CO₂ RMs 8562-8564.

CONCLUSIONS

Multipoint-anchoring of the VPDB δ¹³ C scale provides several distinct "points" on the scale as means for cross-measurements to check the stability and viability of RMs and detect drift of values, if any. This ensures that the δ¹³ C scale is suitable for the most demanding applications, and provides options for developing further RMs with high accuracy inside a robust scale realisation scheme.

Characterisation of new reference materials IAEA-610, IAEA-611 and IAEA-612 aimed at the VPDB δ13 C scale realisation with small uncertainty

RATIONALE

LSVEC, the second anchor Reference Material (RM) for the VPDB δ¹³ C scale realisation, was introduced in 2006. In 2015, its δ¹³ C value was found to be drifting and, in 2017, its use as an RM for δ¹³ C 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 δ¹³ C 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-H₃ PO₄ reaction under well-controlled conditions combined with well-tested stable isotope ratio mass spectrometry.

RESULTS

The assigned values of δ¹³ C 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 δ¹³ C 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 ¹⁷ O 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 δ¹³ C scale in a mutually consistent way. The use of three RMs will allow a consistent realisation of the VPDB δ¹³ C scale with small uncertainty to be established, and to reach metrological compatibility of measurement results over several decades.

Estimation of uncertainty arising from different soil sampling devices: the use of variogram parameters

In the frame of the international SOILSAMP project, funded and coordinated by the National Environmental Protection Agency of Italy (APAT), uncertainties due to field soil sampling were assessed. Three different sampling devices were applied in an agricultural area using the same sampling protocol. Cr, Sc and Zn mass fractions in the collected soil samples were measured by k(0)-instrumental neutron activation analysis (k(0)-INAA). For each element-device combination the experimental variograms were calculated using geostatistical tools. The variogram parameters were used to estimate the standard uncertainty arising from sampling. The sampling component represents the dominant contribution of the measurement uncertainty with a sampling uncertainty to measurement uncertainty ratio ranging between 0.6 and 0.9. The approach based on the use of variogram parameters leads to uncertainty values of the sampling component in agreement with those estimated by replicate sampling approach.

Calculation spreadsheet for uncertainty estimation of measurement results in gamma-ray spectrometry and its validation for quality assurance purpose

An Excel calculation spreadsheet has been developed to estimate the uncertainty of measurement results in γ-ray spectrometry. It considers all relevant uncertainty components and calculates the combined standard uncertainty of the measurement result. The calculation spreadsheet has been validated using two independent open access software and is available for download free of charge at: https://nucleus.iaea.org/rpst/ReferenceProducts/Analytical_Methods/index.htm. It provides a simple and easy-to-use template for estimating the uncertainty of γ-ray spectrometry measurement results and supports the radioanalytical laboratories seeking accreditation for their measurements using γ-ray spectrometry.