Hello, I am using 2 poropak colums in series (not labelled as to which type of poropak, suspect Q or N) and am operating at extremely high sensitivity (TCD) to measure small amounts of CO2. It appears oxygen is interacting with the colums, causing a baseline offset each sample. I guess O2 is being absorbed and released slowly (the baseline drifts down if left for many hours). I cant find much on Poropak apart from little bits in GC books - can anyone help identify whats going on or give me a clue where I can get detailed info about poropak? Thanks

Porapak columns need very careful conditioning. I am not surprised you have baseline drift if you are running your TCD at very high sensitivity, although this obviously depends on column temperature. We use a Methaniser to analyse low levels of CO2, having found that TCD does not give good sensitivity for CO2 with He carrier. What carrier are you using? Waters used to supply Porapak. Hayesep and Chromosorb are other porous polymers which are broadly similar to Porapak. I would ask your instrument manafacturer for technical info on your problem. There are lots of awkward problems to consider with gas analysis, for instance what gas sample valve are you using? What is the difference in specific heat conductance between CO2 and your carrier?
Hope I have not depressed you! Bon chance!

Your question is reasonable but the lack of information makes it difficult to propose a good response. What temperature is your oven? Detector? What instrument and model of detector?
What carrier? Glass or metal columns? What column length, OD, and ID? What kind of union joins the two columns? What is in sample and at what levels? How is sample introduced? How much sample is injected? What levels of CO2 are you measuring? Porapak supports are polymers of different pairs of monomers and can be quite different chemically.
I am sorry to ask so many questions but your question needs more specific background information before anyone can really help you.
best wishes