Preparation Of High-Precision Co2 With Known Triple Oxygen Isotope For Oxygen Isotope Analysis

The objective of this work is to propose a more effective way to prepare an in-house CO2 with known triple oxygen isotope compositions. The major experimental steps include: (1) the O-2 is combusted to CO2 on a graphite rod at 750 degrees C with Pt-catalyst for 3-4 min; and (2) converted CO2 is subsequently purified by two cryogenic traps. The results show high reproducibility of delta C-13 and delta O-18 values of the converted CO2 within 0.010-0.020 parts per thousand and 0.006-0.010 parts per thousand (1 sigma, SD), and the identical delta O-18 value within error with that of the original O-2. Additionally, we have measured the triple oxygen isotope compositions of converted CO2 using an O-2-CO2 Pt-catalyzed oxygen-isotope equilibration method. The measured delta O-17 values of CO2 show high reproducibility within 0.006 parts per thousand (1 sigma, SD), and are identical within error with the original O-2 as well. Notably, our experiments also found that the O-2 with heavier oxygen isotope ratios (delta O-18 > 40 parts per thousand, VSMOW) might have a lesser conversion efficiency, and this effect, combined with the lighter isotope preferential fractionations during the reaction processes of O-2 to CO and CO to CO2, may explain the observed lower O-17/O-16 and O-18/O-16 ratios of the converted CO2 relative to the original O-2.