Junji Yamamoto, Yuuki Hagiwara
By exploiting isotopologue-specific Raman bands, Raman spectroscopic mass spectrometry has emerged as a promising technique for ascertaining the carbon and oxygen isotopic ratios of micrometer-scale CO2 fluids. For this study, we improve the analytical precision of this technique by reanalyzing Raman spectra of CO2 at 10 MPa obtained using a high pixel-resolution spectroscopic configuration [Appl. Opt.64, 2711 (2025)APOPAI0003-693510.1364/AO.557083]. Two curve-fitting procedures were applied to the spectral data. In addition, bandwidth-fluctuation correction was introduced to compensate for instrumental drift affecting fitted peak ratios, based on correlation between fitted peak ratios and variations in Raman bandwidths. Combined application of optimized curve-fitting procedures and bandwidth-fluctuation correction improves the precision of Raman-derived isotopic ratios considerably. Results show that the present method enables determination of 13C/12C and 18O/16O of 10 MPa CO2 fluid, with respective precisions of approximately 2-3‰ and 9-12‰.