Improving the long-term Δ47 reproducibility of the Thermo Scientific 253 Plus 10 kV IRMS using a prototype Peltier cooling device

Carbonate clumped isotope analysis, a relatively new methodology, is still developing rapidly, that is well described by the frequency of changes in the applied methodological conventions. The extent of development is also characterized by the growing, sometimes special, nature of the application areas. Innovations, while promising, can present unforeseen challenges and sometimes brings unexpected difficulties, such as the integration of 10¹³ Ohm resistance in the amplification circuits of Thermo Scientific 253 Plus 10 kV Isotope Ratio Mass Spectrometer (IRMS).

The goal of this improvement was that even very small ion beams can be analyzed with the factor of 3 better signal to noise ratio, which is an important aspect from the point of view of clumped isotope analysis. Unfortunately, 10¹³ Ohm resistance has a significant temperature dependency, which highly influences the magnitude of the detected intensities as well as on the overall long-term stability of the measurement. The daily temperature fluctuation in summer is very significant in Hungary. Under extreme conditions, when the lab's air conditioning could not maintain the desired temperature range, the long-term Δ₄₇ reproducibility of the system achieved an SD = 60 ppm value.

In order to reduce this effect a prototype Peltier cooling device has been installed on the surface of the detector house of our IRMS. To demonstrate the achieved accuracy, precision, and long-term stability (SD <= 30 ppm) of the modified measurement system, we present results of clumped isotope analyses of international carbonate standard samples and naturally formed travertine samples (known formation temperatures are in the range of 5-95°C) and compare them with formerly published data of two reputable laboratories from the clumped community, which use different measurement equipment:

• ETHZ: Thermo Scientific MAT253 IRMS and Kiel IV automatic carbonate device [1]
• MIT: Nu Perspective IRMS and NuCarb automated sample preparation unit [2]

Additionally, we offer insight into the infrastructure and analytical methodology of the clumped isotope laboratory established at ICER (ATOMKI, Debrecen, Hungary). The modification implemented and the attained long-term stability may serve as a valuable reference for other laboratories encountering similar challenges.

Keywords: carbonate clumped isotope, Peltier cooling, long-term reproducibility

References

[1] Bernasconi, S. M., I. A. Müller, K. D. Bergmann, et al. (2018) Reducing uncertainties in carbonate clumped isotope analysis through consistent carbonate-based standardization. Geochemistry, Geophysics, Geosystems, v. 19, 2895-2914.

[2] Anderson, N. T., J. R. Kelson, S. Kele et al. (2021) A Unified Clumped Isotope Thermometer Calibration (0.5–1,100°C) Using Carbonate-Based Standardization. Geophysical Research Letters, v. 48, e2020GL092069.