Use of Laser Spectroscopy To Measure the 13C/12C and 18O/16O Compositions of Carbonate Minerals

The stable carbon and oxygen isotope compositions of carbonate minerals are utilized throughout the earth and environmental sciences for various purposes. Here, we demonstrate the first application of a prototype instrument, based on off-axis integrated cavity output laser spectroscopy, to measure the carbon and oxygen isotope composition of CO2 gas evolved from the acidification of carbonate minerals. The carbon and oxygen isotope ratios were recorded from absorp-tion spectra of (COO)-C-12-O-16-O-16, (COO)-C-13-O-16-O-16, and (COO)-C-12-O-16-O-18 in the near-infrared wavelength region. The instrument was calibrated using CaCO3 minerals with known delta C-13(VPDB) and delta O-18(VSMOW) values, which had been previously calibrated by isotope ratio mass spectrometry relative to the international isotopic standards NBS 18 and NBS 19. Individual analyses are demonstrated to have internal precision (1 SE) of better than 0.15%o for delta C-13 and 0.6 parts per thousand for delta O-18. Analysis of four carbonate standards of known isotopic composition over 2 months, determined using the original instrumental calibration, indicates that analyses are accurate to better than 0.5 parts per thousand for both delta C-13 and delta O-18 without application of standard-sample-standard corrections.