The effects of carrier gas and flow rate on residence time. A) CO2 signal (black, blue, green, and red) and temperature (orange) vs. time for two different flow rates of N2 and He carrier gases. All runs were done at 30 mbar with a 35°C/minute ramp rate. Temperature data shown are for a run using. He carrier gas. The high diffusivity of CO2 in He make it very difficult to pump from our system, and the residual CO2 is ~10x higher than the N2 carrier gas runs at the same flow rates. The large dip in CO2 pressure at ~3300 seconds, most apparent in the 3sccm He data is caused by the back reaction of residual CO2 with CaO to form CaCO3 when the sample is cooling. B) The ratio of the mass 44 background to the mass 44 signal at t1 (marked in A). Levels of CO2 in the N2 carrier gas return to baseline levels at ~10sccm as opposed to 20 for He. It is clear that for systems with a large chamber volume, N2 is much more effective at removing evolved gas products than He at almost any flow rate.