Carbon dioxide (CO2) gas is produced from the pretreated residue of samples and purified for graphitisation.

Samples are combusted at 900oC for 4 hours in evacuated, sealed quartz tubes with cupric oxide and silver wire. The cupric oxide provides oxygen for the combustion and the silver isolates sulphur and halogens in a solid form.

After combustion, the CO2 is cryogenically purified by passing it through traps of ethanol/dry ice to remove water. The purified CO2 is collected in a glass vessel for transport to the graphitisation and mass spectrometry laboratories.