Use of laser spectroscopy to measure the δ13C and δ18O compositions of carbonate minerals

The stable carbon and oxygen isotope composition 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 (OA-ICOS), to measure the carbon and oxygen isotope composition of CO2 gas evolved from the acidification of carbonate minerals. The isotopic specific measurements of δ13C and δ18O were recorded from absorption spectra of 12C16O16O, 13C16O16O and 12C16O18O in the near-infrared wavelength region. The instrument was calibrated using CaCO3 minerals with a known δ13C and δ18O compositions, 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 of better than 0.15 ‰ for δ13C and 0.6 ‰ for δ18O. Analysis of 4 carbonate standards of known isotopic composition over 2 months, determined using the original instrumental calibration, indicates that analyses are accurate, with accuracy of better than 1 ‰ for δ18O and better than 0.5 ‰ for δ13C. In comparison to CF-IRMS, OA-ICOS offers an extremely cost-effective, low power, and robust mechanism for measuring the stable isotopic composition of carbonate minerals, as it uses very few consumables, can be used by non-expert users, and the instrument can be easily deployed into field-based research environments.