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.