High-Precision Measurement of ¹⁸⁶Os/¹⁸⁸Os and ¹⁸⁷Os/¹⁸⁸Os: Isobaric Oxide Corrections with In-Run Measured Oxygen Isotope Ratios

We present a novel method for high precision measurement of ¹⁸⁶Os/¹⁸⁸Os and ¹⁸⁷Os/¹⁸⁸Os ratios, applying isobaric oxide interference correction based on in-run measurements of oxygen isotopic ratios. For this purpose, we set up a static data collection routine to measure the main Os¹⁶O₃^– ion beams with Faraday cups connected to conventional 10¹¹ amplifiers, and ¹⁹²Os¹⁶O₂¹⁷O^– and ¹⁹²Os¹⁶O₂¹⁸O^– ion beams with Faraday cups connected to 10¹² amplifiers. Because of the limited number of Faraday cups, we did not measure ¹⁸⁴Os¹⁶O₃^– and ¹⁸⁹Os¹⁶O₃^– simultaneously in-run, but the analytical setup had no significant influence on final ¹⁸⁶Os/¹⁸⁸Os and ¹⁸⁷Os/¹⁸⁸Os data. By analyzing UMd, DROsS, an in-house Os solution standard, and several rock reference materials, including WPR-1, WMS-1a, and Gpt-5, the in-run measured oxygen isotopic ratios were proven to present accurate Os isotopic data. However, ¹⁸⁶Os/¹⁸⁸Os and ¹⁸⁷Os/¹⁸⁸Os data obtained with in-run O isotopic compositions for the solution standards and rock reference materials show minimal improvement in internal and external precision, compared to the conventional oxygen correction method. We concluded that, the small variations of oxygen isotopes during OsO₃^– analytical sessions are probably not the main source of error for high precision Os isotopic analysis. Nevertheless, use of run-specific O isotopic compositions is still a better choice for Os isotopic data reduction and eliminates the requirement of extra measurements of the oxygen isotopic ratios.