Three certified sugar reference materials for carbon isotope delta measurements

Abstract

Rationale For isotope delta analysis, it is preferable to have at least two matrix‐matched reference materials whose isotope delta values encompass those of the samples to be analyzed. The National Research Council Canada (NRC) has developed three sugar Certified Reference Materials (CRMs), BEET‐1 (beet sugar), GALT‐1 (galactose), and FRUT‐1 (fructose), to be collectively used for carbon isotope delta measurements in sugars, and other organic materials. Methods All materials were homogenized and packaged in glass ampules. All three sugar materials were analyzed at the NRC using elemental analyzer/isotope ratio mass spectrometry (EA/IRMS). Six additional laboratories also provided EA/IRMS measurements. Data from all laboratories were re‐normalized using three international secondary reference materials (IAEA‐CH‐6, USGS40, and USGS62) included as blind samples in the inter‐laboratory comparison, thus providing added quality control and robustness to the study. Results Re‐normalized carbon isotope delta values from each laboratory were combined using a random laboratory effects statistical model with accounting of the correlations between the laboratory results due to the use of the same reference materials for calibration. The consensus δ(13C) values and combined standard uncertainties which include effects due to characterization, homogeneity, and stability for BEET‐1, GALT‐1, and FRUT‐1 are −26.02(7) ‰, −21.41(6) ‰, and −10.98(5) ‰, respectively, on the VPDB scale. Conclusions Three new δ(13C) sugar CRMs (BEET‐1, GALT‐1, and FRUT‐1) were developed and are available from NRC. These three CRMs can be utilized as a set for daily δ(13C) scale normalization of sugar‐based or other organic materials in order to produce reliable δ(13C) measurements.

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

“…Based on high-precision isotope-ratio mass spectrometry (IRMS), 8,9 a consensus value of −46.6 mUr exactly was assigned to LSVEC lithium carbonate. 10,11 The results ( 10,11 The adoption of two-point normalization improved the standard uncertainties of δ 13 C RMs significantly compared with previously assessed uncertainties, as demonstrated in Figure 1 of Coplen et al 10 Since then, determinations of δ 13 C values of most new secondary RMs for forensic, environmental, paleontological, and atmospheric applications [12][13][14][15][16][17][18][19][20] Gaithersburg, MD, USA). 21,22 Subsequently, this observation was confirmed by Qi et al 14 Thus, LSVEC no longer meets minimum requirements for use as a δ 13 C RM, particularly as a scale anchor, and IUPAC has advised against its use as a δ 13 C RM.…”

“…Following recommendations of the Commission on Isotopic Abundances and Atomic Weights (CIAAW) in August 2005 at the 43rd General Assembly of IUPAC in Beijing and recommendations of an IAEA panel, a recommendation evolved that δ 13 C values of all carbon‐bearing materials should be measured and expressed relative to VPDB on a scale normalized by assigning consensus values of −46.6 mUr to LSVEC lithium carbonate and +1.95 mUr to NBS 19 calcium carbonate 10,11 . The adoption of two‐point normalization improved the standard uncertainties of δ 13 C RMs significantly compared with previously assessed uncertainties, as demonstrated in Figure 1 of Coplen et al 10 Since then, determinations of δ 13 C values of most new secondary RMs for forensic, environmental, paleontological, and atmospheric applications 12–20 have been based on the NBS 19‐LSVEC scale with NBS 19 and LSVEC as anchors. An IUPAC technical report, which assessed international RMs for isotope‐ratio measurements, published in 2014 by Brand et al, 1 tabulates a comprehensive list of δ 13 C values of RMs on the NBS 19‐LSVEC scale.…”

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

“…It was also a requirement to present a clear hierarchical structure of RMs on the VPDB scale, verify the compatibility of existing RMs and, correspondingly, present a self‐consistent revision of the VPDB δ 13 C scale 3 . The importance of self‐consistency in the value assignment of modern RMs has been stressed recently 7,8 …”

“…3 The importance of self-consistency in the value assignment of modern RMs has been stressed recently. 7,8 In 2017, the 19th World Meteorological Organization (WMO)/ IAEA Meeting on Greenhouse Gas Measurement Techniques (GGMT-2017) highlighted these needs and requested that "potentially a range of materials may be introduced to help identify drift" and that the new RMs "must be stable, homogenous, sufficiently abundant, and cover the δ 13 C range of interests" (cited from GAW Report No. 242 9 ).…”

On the metrological traceability and hierarchy of stable isotope reference materials aimed at realisation of the VPDB scale: Revision of the VPDBδ13C scale based on multipoint scale‐anchoring RMs

“…It was stressed that the IAEA as provider of the highest level (primary) scale calibrators must take a leading role in developing these new RMs that can be used by WMO central calibration laboratories (CCLs) to produce fit-for-purpose specific materials of a suitable matrix, for example, CO 2 -in-air or CH 4 -in-air. 7,8 In addition, some recent publications have highlighted the need for self-consistency (some publications call it "coherency" 23 ) of RM values. 23,24 In developing new RMs that address these concerns, a revision of the concept of the existing VPDB scale realisation, several questions occurred: i.…”