Improved precision of Raman-derived 13 C/ 12 C and 18 O/ 16 O in CO 2 using bandwidth-fluctuation correction and optimized curve-fitting procedures

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 CO 2 fluids. For this study, we improve the analytical precision of this technique by reanalyzing Raman spectra of CO 2 at 10 MPa obtained using a high pixel-resolution spectroscopic configuration [ Appl. Opt. 64 , 2711 ( 2025 ) APOPAI 0003-6935 10.1364/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 13 C/ 12 C and 18 O/ 16 O of 10 MPa CO 2 fluid, with respective precisions of approximately 2–3‰ and 9–12‰.