Chromatography Forum

I'm using Carboxen 1006 and Molesieve 5A PLOT columns in series for gas analysis. The temperature limit of the Carboxen 1006 is 250 C whereas the Molesieve 5A PLOT column has a temperature limit of 300 C. I really need to condition the Molesieve 5A column towards its upper temperature of 300 C but this would exceed the temperature limit of the Carboxen 1006 column.

I could take the Carboxen 1006 out of the oven in order to condition the Molesieve 5A column at a higher temperature than 250 C but I'd rather not mess with the columns. Would I get sufficient conditioning of the Molesieve 5A column if I simply conditioned for several hours at 250 C as a compromise? How far/long could I push past the temperature limit of the Carboxen 1006 before it degrades?

To me, columns are too expensive to play risky games with them. I would error on the side of safety and only go to the maximum safe temperature on the Carboxen phase.

What is your application on the molecular sieve? If you're looking for light gases (H2, O2, N2, CH4 and CO) they all come out at temperatures near RT. Conditioning at 300 °C won't help you much.

The elution order of methane and CO on a Molsieve column will depend on the water content of the Mole Sieve column. If the water content is 2%, CO will elute after methane. For a water content of 4%, CO and methane will elute together, and with a water contant of 9%, CO will elute before methane. This information is given in an old bulletin (760A) from Supelco dated 1976. The water content will be dependent on the conditioning temperature.

Gasman

Great answer GasMan, my experience with methane and CO seems to indicate that's the case. The better conditioning, the better the separation and retention of both those gases.