Enabling scientific discovery through stable isotope analysis
Analysis of Carbonate δ13C δ18O
Summary: We use a Kiel III Carbonate Device coupled to a Finnigan Delta Plus for a dual-inlet based δ13C and δ18O measurement of small carbonate samples.

Reference Materials: We employ carbonate international reference materials NBS19 and L-SVEC to put our δ13C and NBS19 and NBS18 to put our δ18O carbonate samples on the VPDB scale. We have a suite of internal reference materials that span the same range of NBS19, L-SVEC, and NBS18 for day to day analysis.

Sample submission: If you would like to submit carbonate samples for δ13C and δ18O analysis, please have your samples ground to a fine powder and in a uniquely and simply labeled container. We require 20 to 120 µg of carbonate for a single analysis. Please send enough sample material so as to provide ~200 µg of carbonate. Please include in your shipment container the following form (pdf or doc).

Exhaustive description of analysis: The Kiel III carbonate device is an automated system for the digestion of carbonate with 100% phosphoric acid (specific gravity 1.90 - 1.92) and purification of the carbon dioxide (CO2) product. For traditional pure-carbonate samples, three drops of phosphoric acid are dropped onto 20-120 µg of carbonate in an evacuated, leak tested, pyrex reaction vessel and allowed to react for ten minutes at 70 *C. Both CO2 and H2O are trapped in a small volume cold finger held at -196 *C with liquid nitrogen. When the reaction is complete, the trap is warmed to -110 *C to keep H2O but allow CO2 to expand for gas volume measurement. The CO2 is then frozen into a second small volume cold finger trap held at -196 *C with liquid nitrogen. Once complete, the trap is warmed to 26 *C allowing the CO2 to pass into a Finnigan Delta Plus isotope ratio mass spectrometer (IRMS) via a dedicated capillary for mass / charge 44, 45, 46 measurement alternately with that of a reference CO2 gas roughly calibrated to the VPDB scale held in a variable volume bellow. Eight comparisons of sample / reference are made to yield initial raw δ13C and δ18O values.

Calculations: Here is a pdf containing the specific details of our reference materials and corrections.

Suggested reading:

McCrea JM. On the isotopic chemistry of carbonates and a paleotemperature scale. Journal of Chemical Physics, 18, 849-857. (1950).
Coplen TB, Kendall C, Hopple J. Comparison of stable isotope reference samples. Nature, 302, 236-238. (1983).
Tobin TS, Schauer AJ, Lewarch E. Alteration of micromilled carbonate δ18O during Kiel Device analysis. Rapid Commun. Mass Spectrom., 25, 2149-2152. (2011).