Characterisation of new reference materials IAEA‐610, IAEA‐611 and IAEA‐612 aimed at the VPDB δ <sup>13</sup> C scale realisation with small uncertainty
Bibliographic record
Abstract
Rationale LSVEC, the second anchor Reference Material (RM) for the VPDB δ 13 C scale realisation, was introduced in 2006. In 2015, its δ 13 C value was found to be drifting and, in 2017, its use as an RM for δ 13 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 δ 13 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 CO 2 preparation and stable isotope measurements was used, namely carbonate‐H 3 PO 4 reaction under well‐controlled conditions combined with well‐tested stable isotope ratio mass spectrometry. Results The assigned values of δ 13 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 δ 13 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 δ 13 C scale in a mutually consistent way. The use of three RMs will allow a consistent realisation of the VPDB δ 13 C scale with small uncertainty to be established, and to reach metrological compatibility of measurement results over several decades.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.007 | 0.007 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.006 | 0.002 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.002 | 0.002 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.005 | 0.004 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".