<scp>OU</scp>‐9: A Potential Reference Material with High <scp>⁸⁷Rb</scp>/<scp>⁸⁶Sr</scp> and <scp>⁸⁷Sr</scp>/<scp>⁸⁶Sr</scp> for Data Quality Control and Method Validation in <scp>ID</scp>‐<scp>MS</scp> Rb

The use of ID‐MS (ID‐TIMS/MC‐ICP‐MS) techniques to characterise reference materials (RM) with high Rb/Sr and 87 Sr/ 86 Sr for in situ LA‐ICP‐MS‐MS Rb‐Sr geochronology is highly important. However, there is a lack of well‐characterised RMs with high Rb/Sr and 87 Sr/ 86 Sr ratios to effectively monitor data quality for ID‐TIMS/MC‐ICP‐MS Rb‐Sr geochronology. In this study, a pegmatite RM, OU‐9, was comprehensively characterised using ID‐TIMS/MC‐ICP‐MS techniques. Measurements undertaken on OU‐9 yielded mass fractions of 2494 ± 22 μg g ‐1 for Rb, 36.05 ± 0.25 μg g ‐1 for Sr, as well as isotope ratios of 832.4 ± 5.2 for 87 Rb/ 86 Sr and 32.60 ± 0.19 for 87 Sr/ 86 Sr. Despite the presence of inhomogeneity within and between RM sachets, regarding Rb‐Sr isotope systematics at sampling scales of ~ 10 mg and even 0.2 g, 87 Rb/ 86 Sr and 87 Sr/ 86 Sr values derived from the analyses align well along the reference isochron. This alignment yields a model age of ~ 2650 Ma with an initial 87 Sr/ 86 Sr of ~ 1.2. We advocate that OU‐9 could serve as a potential RM for ID‐TIMS/MC‐ICP‐MS Rb‐Sr data quality control for materials characterised by high 87 Rb/ 86 Sr and 87 Sr/ 86 Sr ratios. The data quality of individual measurement results can be assessed based on their fit to the correlation line.