Precision and long-term stability of clumped-isotope analysis of CO2 using a small-sector isotope ratio mass spectrometer


O. Abe, Graduate School of Environmental Studies, Nagoya University, Nagoya 464–8601, Japan.




The ratio of the measured abundance of 13C–18O bonding CO2 to its stochastic abundance, prescribed by the δ13C and δ18O values from a carbonate mineral, is sensitive to its growth temperature. Recently, clumped-isotope thermometry, which uses this ratio, has been adopted as a new tool to elucidate paleotemperatures quantitatively.


Clumped isotopes in CO2 were measured with a small-sector isotope ratio mass spectrometer. CO2 samples digested from several kinds of calcium carbonates by phosphoric acid at 25 °C were purified using both cryogenic and gas-chromatographic separations, and their isotopic composition (δ13C, δ18O, Δ47, Δ48 and Δ49 values) were then determined using a dual-inlet Delta XP mass spectrometer.


The internal precisions of the single gas Δ47 measurements were 0.005 and 0.02 ‰ (1 SE) for the optimum and the routine analytical conditions, respectively, which are comparable with those obtained using a MAT 253 mass spectrometer. The long-term variations in the Δ47 values for the in-house working standard and the heated CO2 gases since 2007 were close to the routine, single gas uncertainty while showing seasonal-like periodicities with a decreasing trend. Unlike the MAT 253, the Delta XP did not show any significant relationship between the Δ47 and δ47 values.


The Delta XP gave results that were approximately as precise as those of the MAT 253 for clumped-isotope analysis. The temporal stability of the Delta XP seemed to be lower, although an advantage of the Delta XP was that no dependency of δ47 on Δ47 was found. Copyright © 2012 John Wiley & Sons, Ltd.