Hello all, I'm hoping someone can shed some light on a problem I am having (GC-IRMS, MAT252). My background levels for CO2 are elevated, but on masses 45 and 46 only. The source seems to be my Nafion trap, as the 45 (and 46) signal increases drastically (perhaps 200mV) when I heat the trap, and falls to normal when the trap is removed. Mass 44 is unaffected throughout all of this (~9mV). I replaced the Nafion tubing, but am still getting the same problem. Another trap in the lab made from the same batch is working fine. Does anyone have any suggestions? What compound can give masses 45 and 46 but not 44? Nafion is a fluorinated polymer, but the only fluorine compound I can dream up that has a mass of 45 is NCF. Doesn't seem very likely.... Paul Eby [log in to unmask] Biogeochemistry Lab School of Earth and Ocean Science University of Victoria phone: 250-721-6183 fax: 250-472-4620