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

Abstract In this study, we performed a detailed comparison of stable and clumped isotopic data for an extraction method passing CO 2 through a Porapak Q absorbent trap (PQT) driven by liquid nitrogen (LN method), an extraction method passing CO 2 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 Δ 47 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 Δ 48 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 Δ 47 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 CO 2 extraction methods for clumped isotope analysis.