Evaluation of accuracy and precision of oxygen isotope ratios in calcite using Raman mass spectrometry

Abstract

Raman spectra of calcite show peaks at 1086 cm^-1 and 1065 cm^-1, corresponding to ¹²C¹⁶O₃ and ¹²C¹⁶O¹⁶O¹⁸O, respectively (e.g., Gillet et al., 1996). The precision of oxygen isotope ratio measurements in calcite using the intensity ratio of these peaks has been reported to be better than 3 per mil (Inoue et al., 2024). However, the accuracy of this method has not yet been fully evaluated.In this study, we examined the accuracy of oxygen isotope ratio measurements using Raman mass spectrometry, based on the intensity ratios of isotopologues in synthetic calcite. A correlation (R² = 0.72) was observed between the Raman peak intensity ratio and the oxygen isotope ratio. Using this relationship, the oxygen isotope ratio of IAEA-603 was estimated to be 28 +/- 10 per mil, suggesting that the method has a certain level of validity for estimating oxygen isotope ratios.