Determination of clumped isotopes in carbonate using isotope ratio mass spectrometer: Effects of extraction potential and long-term stability

• Extraction potential (EP) governs accuracy and precision of CO2 clumped isotope data.
• 90% EP (∼−4.5% of accelerating voltage) is optimal for our MAT253 mass spectrometer.
• We got a stable linearity of mass spectrometer for clumped isotope analysis (CIA).
• Repeated measurements on NBS 19 demonstrate long-term reproducible Δ47 values.
• Stable linearity enables CIA without frequently renewing heated gas line calibration.

In this study, we developed an instrument tuning method for analyzing clumped isotope on carbonates using isotope ratio mass spectrometer (IRMS). The ion source extraction potential is found governing accuracy and precision for CO2 clumped isotope analysis, with 90% extraction as an optimum parameter. Under this condition, we obtained a relatively stable linearity of mass spectrometer, as shown by little variation in slopes (0.0075–0.0077) for three heated CO2 gas lines (plot of Δ47 vs. δ47) observed over a period of one year. By contrast, the intercepts of the heated gas lines displayed a larger variation, ranging from −0.79‰ to −0.89‰, which may be partially contributed by some artificial factor, e.g., variable cooling rates of heated CO2 gases. Nevertheless, repeated measurements on NBS 19 demonstrate long-term reproducible Δ47 values, comparable with previously published results. The stable linearity of the IRMS results ensures that clumped isotopes can be analyzed precisely without frequently constructing a reference frame through heated CO2 gases. Our results provide a basis for optimizing IRMS performance for clumped isotope analysis.

Figure optionsDownload high-quality image (118 K)Download as PowerPoint slide