TILDAS

Quality control protocols for TILDAS-based measurements of triple oxygen isotopes in CO₂ integrate emerging community standards and methodologies to ensure precision, accuracy, and long-term reproducibility. Every sixth sample run is a carbonate reference material—either NBS18 or IAEA603—interleaved systematically to monitor instrumental drift, facilitate correction of scale compression, and track analytical stability. This bracketing strategy is consistent with best practices reported by Hare et al. (2022), Perdue et al. (2022), and Bajnai et al (2023), who demonstrated that regular reference measurements are critical for achieving sub-per mil precision in Δ′¹⁷O determinations. Known-unknown materials with independently established δ¹⁸O and Δ′¹⁷O values are also run routinely to assess method accuracy and internal reproducibility over time, providing a second tier of quality control.

Corrections for the concentration dependence of isotopic measurements, particularly as it affects δ¹⁸O and δ¹⁷O via pressure broadening and baseline offsets, are implemented following approaches outlined in Hare et al. (2022), Steur et al. (2021) and Bajnai et al. (2023). These corrections are derived from in-house calibration curves using dilutions of reference CO₂ and are applied on a per-sample basis. In addition, UCT participates in international interlaboratory exercises, including IAEA-led triple oxygen isotope intercomparison campaigns, which help benchmark performance against global standards and ensure metrological traceability. This external validation complements internal data scrutiny—such as monitoring of acid digestion yields, spectral residuals and concentration-normalised Xp values (cf. Griffith, 2012)—to flag and exclude outliers and maintain the integrity of the analytical dataset.