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