Determination of clumped isotopes in carbonate using isotope ratio mass spectrometry: Toward a systematic evaluation of a sample extraction method using a static Porapak™ Q absorbent trap

• Three sample extraction methods were systematically evaluated to examine efficiency.
• Optimum collection time for LN method was 35 min with Porapak Q trap at −15 °C.
• Optimum collection time for LN + HV method was 25 min with Porapak Q trap at −25 °C.
• LN + HV method at −25 °C PQT can remove contaminants as same efficient as LN method.
• LN + HV method at −25.0 °C PQT may serve as a promising sample preparation method.

In this study, we performed a detailed comparison of stable and clumped isotopic data for an extraction method passing CO2 through a Porapak Q absorbent trap (PQT) driven by liquid nitrogen (LN method), an extraction method passing CO2 through a PQT driven by liquid nitrogen and high vacuum pumping (LN + HV method) and an extraction method without a PQT (NAT method), to examine the effectiveness and reliability of these methods. Changes in raw Δ47 values along with collection times were used to constrain the optimum collection time (OCT) for each method. The OCT for the LN method shortened considerably when the PQT was warmer, i.e., from ∼35 min to ∼30 min when the PQT temperature changed from −15 °C to −12.5 °C. In contrast, the OCT for the LN + HV method displayed little change with the PQT temperature and was reduced to 25 min for both −15 °C and −25 °C. The contaminant removal efficiency of these methods was evaluated by Δ48 values, revealing that the LN method (with a −12.5 °C to −25 °C PQT) and the LN + HV method (at −25 °C) could effectively remove contaminants compared with the NAT method. Therefore, the LN + HV method (at −25.0 °C) may serve as a promising sample preparation method for routine measurement because it can save time without compromising sample cleaning efficiency. Nevertheless, the LN + HV method yielded Δ47 values 0.04–0.05‰ higher than the LN method at the same temperature, possibly because of different absorption–desorption states of the PQT in these methods. These findings provide useful clues for optimizing CO2 extraction methods for clumped isotope analysis.

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