With a GC with PED
Using Hayesep D 10' mesh 100/120(porous polymer) with a heartcut configuration, why is there a strange round bump during the CO2 integration time.

When I run a cycle with 1ppm CO2 in Helium, there is a nice CO2 peak.

However, when I run pure O2, I got a strange round bump during CO2 integration.

Is someone knows if it comes from the columns or the sample gas???