Instruments
Standard and higher resolution Thermo 253+ Mass Specs / Kiel IV’s
Sample Material
Pure calcium carbonate (calcite) only.
Sample Size
Normally 30 to 140 μg. Larger samples can be run, but the CO2 gas will be subsamples (aka chopped) before analysis. Higher resolution 253+ allows for sample sizes down to approximately 7μg.
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-IV (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 253+ mass spectrometer where it is analyzed by dual inlet mass spectrometry.
