Michelle Chartrand, Juris Meija and Zoltan Mester

Metrology, National Research Council Canada

Dual inlet measurements of CO₂ are considered the holy grail of isotopic measurements, with uncertainties usually a magnitude lower than those obtained from EA-IRMS.  However, these measurements require numerous tedious steps such as converting carbonates to CO₂ gas, sample introduction techniques, and low-throughput sampling regimes. A project was undertaken at NRC to characterize the carbon and oxygen isotope delta values of 13 CO₂ gas cylinders with nominal δ_VPDB(¹³C) values ranging from +10 to -40 ‰. Strategies for cross-contamination evaluation, and carbon and oxygen isotope delta value assignment via three different calibration techniques: direct measurement, calibration curve and global least squares adjustment involving 1000+ measurements, will be presented. The results will demonstrate that NRC can measure carbon and oxygen isotope delta measurements of CO₂ gas with standard precisions of 0.01 ‰ and 0.04 ‰, respectively.