Stable isotope ratios ( 18 O/ 16 O, 13 C/ 12 C, and 17 O/ 16 O) in carbonates have contributed greatly to the understanding of Earth and planetary systems, climates, and history. The current method for measuring isotopologues of CO 2 derived from CaCO 3 is primarily gas-source isotope ratio mass spectroscopy (IRMS). However, IRMS has drawbacks, such as mass overlap by multiple CO 2 isotopologues and contaminants, the requirement of careful sample purification, and the use of major instrumentation needing permanent installation and a high power electrical supply. Here, we report simultaneous 18 O/ 16 O, 13 C/ 12 C, and 17 O/ 16 O analyses for microgram quantities of CaCO 3 using a tunable mid-infrared laser absorption spectroscopy (TILDAS) system, which has no mass overlap problem and yields high sensitivity/precision measurements on small samples, as small as 0.02 μmol of CO 2 (equivalent to 2 μg of CaCO 3 ) with standard errors of less than 0.08 ‰ for 18 O/ 16 O and 13 C/ 12 C (±0.136 ‰ and ±0.387 ‰ repeatability; n = 10). In larger samples of CO 2 , 0.68 μmol (or 68 μg of CaCO 3 ), standard error is less than 0.04 ‰ for 18 O/ 16 O and 13 C/ 12 C (< ±0.1 ‰ repeatability; n = 10) and 0.03 ‰ for 17 O/ 16 O (±0.069 ‰ repeatability; n = 10). We also show, for the first time, the relationship between 17 O/ 16 O ratios measured using the TILDAS system and published 17 O values of international standard materials (NBS-18 and -19) measured by IRMS. The benchtop TILDAS system, with cryogen-free sample preparation vacuum lines for microgram quantities of carbonates, is therefore a significant advance in carbonate stable isotope ratio geochemistry and is a new alternative to conventional IRMS.
ASJC Scopus subject areas
- Analytical Chemistry