Carbonate Analysis δ13C and δ18O

Sample Material: Pure calcium carbonate (calcite) only.

Sample Size: 40 to 140 µg. Larger samples can be run, but the CO2 gas will be subsamples (aka chopped) before analysis.

Sample Preparation: A fine-grained powder is required. However, foraminifera (150-300 microns) are typically analyzed whole. Pretreating to remove organic matter (a contaminate for δ13C analysis) may be required.

Precision: ±0.05 permil for δ18O and ± 0.03 for δ13C.

Method: Using the Kiel III (Fig. 1.) preparation device samples are reacted with ~105% orthophosphoric acid (see acid preparation method) at 70°C for 5 minutes. The evolved CO2 and H2O gases are trapped (i.e., frozen at < -180°C) in coldfinger 1. The Non-condensable gases are then removed and the CO2 is transferred into a second coldfinger (< -180°C) while the water is retained in coldfinger 1 (-100°C). After the second trapping is complete the CO2 is thawed and transferred via a capillary into the MAT 252 mass spectrometer where it is analyzed by dual inlet mass spectrometry.

Figure 2.

Figure 1.

Suggested Reading:

McCrea, J.M. (1950). On the isotopic chemistry of carbonates and a paleotemperature scale.  Journal of Chemical Physics, 18 (6), 849-857.

Pier, A. de Groot (2009). Carbon (13C/12C) and Oxygen (18O/16O) Isotopes in Carbonate Rocks and Mineral.  In: Handbook of Stable Isotope Analytical Techniques, Volume 2, p. 273-329.