II. Converting Sample to CO₂

    At the end of the chemical cleaning, the samples are dried and then inspected. A sample is then ready for conversion to a form in which it can be placed in the accelerator mass spectrometer for analysis. A few milligrams of the cleaned sample is placed in a glass tube along with some cleaned copper oxide. The tube is attached to a vacuum system and evacuated. Some samples such as charcoal and wood are heated to about 900°C to produce carbon dioxide. Others such as mixtures are heated to about 400°C. CO₂ is produced along with water and nitrogen oxides.

    The pressure of cleaned and dried CO₂ gas is measured in a known volume, and from that, the carbon content of the sample is calculated. Yields of 40-45% carbon are typical from most organic materials.

    Carbonaceous samples do not need to go through combustion process. Samples are placed in the tube and dissolved by phosphoric acid. This reaction liberates carbon dioxide gas which is then collected in the known volume.