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Paleo Slide Set: Climate and the Classic Maya Civilization
Front view of a gaseous-source stable isotope mass spectrometer.
Oxygen isotopes of CaCO3 are measured by reacting the shells in phosphoric acid at constant temperature. An automated preparation device consisting of a carousel that holds 44 samples, a glass reaction vessel containing phosphoric acid and water jacket kept at 90 degrees C is used in the process. Samples are loaded into the stainless steel carrying boats and dropped into a common acid bath. The products of the reaction are water, which is trapped cryogenically at approximately 100 degrees C, and carbon dioxide, which is trapped at liquid nitrogen temperature: 3CaCO3 (shells) + 2H3PO4 (phosphoric acid) yields 3CO2 (carbon dioxide gas) + H2O (water) + Ca(PO4)2 (calcium phosphate). The oxygen isotope ratios of the carbon dioxide are measured using a mass spectrometer. The entire system is automated for a large throughput of samples.

Photo Credits:
David A. Hodell
Department of Geology, University of Florida
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Last Modified: 12 October 2001

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