The purified CO 2 is collected in a glass vessel for transport to the graphitization and mass spectrometry laboratories. The final step in sample processing is the conversion of the sample CO 2 to elemental carbon graphite. In the graphitization laboratory, the sample CO 2 is mixed with a stoichiometric amount of hydrogen gas inside a glass reaction vessel. The reaction vessel contains a small amount of iron powder which will act as a catalyst for the reaction. The reaction vessel is placed in a 700 o C furnace and in about 5 hours the CO 2 converts to graphite.
Water is trapped out as a by-product of the reaction.
It is standard procedure to measure d 13 C on all samples, using conventional mass spectrometry. The cost of this is included in the overall price of the AMS measurement.