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

Rapid Communications in Mass Spectrometry
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The stable carbon isotopic (δ13C) reference material (RM) LSVEC Li2CO3 has been found to be unsuitable for δ13C standardization work because its δ13C value increases with exposure to atmospheric CO2. A new CaCO3 RM, USGS44, has been prepared to alleviate this situation.


USGS44 was prepared from 8 kg of Merck high-purity CaCO3. Two sets of δ13C 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 CaCO3 (δ13CVPDB = +1.95 milliurey (mUr) exactly, where mUr = 0.001 = 1‰), and LSVEC Li2CO3 (δ13CVPDB = −46.6 mUr exactly), and normalized to the two-anchor δ13CVPDB-LSVEC isotope-delta scale. The second set of values was obtained by dual-inlet (DI)-IRMS of CO2 evolved by reaction of H3PO4 with carbonates, corrected for cross contamination, and normalized to the single-anchor δ13CVPDB scale.


USGS44 is stable and isotopically homogeneous to within 0.02 mUr in 100-μg amounts. It has a δ13CVPDB-LSVEC value of −42.21 ± 0.05 mUr. Single-anchor δ13CVPDB values of −42.08 ± 0.01 and −41.99 ± 0.02 mUr were determined by DI-IRMS with corrections for cross contamination.


The new high-purity, well-homogenized calcium carbonate isotopic reference material USGS44 is stable and has a δ13CVPDB-LSVEC value of −42.21 ± 0.05 mUr for both EA/IRMS and DI-IRMS measurements. As a carbonate relatively depleted in 13C, it is intended for daily use as a secondary isotopic reference material to normalize stable carbon isotope delta measurements to the δ13CVPDB-LSVEC scale. It is useful in quantifying drift with time, determining mass-dependent isotopic fractionation (linearity correction), and adjusting isotope-ratio-scale contraction. Due to its fine grain size (smaller than 63 μm), it is not suitable as a δ18O reference material. A δ13CVPDB-LSVEC value of −29.99 ± 0.05 mUr was determined for NBS 22 oil.

Publication type Article
Publication Subtype Journal Article
Title USGS44, a new high-purity calcium carbonate reference material for δ13C measurements
Series title Rapid Communications in Mass Spectrometry
DOI 10.1002/rcm.9006
Volume 35
Issue 4
Year Published 2021
Language English
Publisher Wiley
Contributing office(s) WMA - Laboratory & Analytical Services Division
Description e9006, 17 p.
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