Chromatography Forum

can a gc column be baked out over night at the upper temperature limit(lets say 12hours) without adverse affects to the column.

I know that the column will lose stationary phase over time but when is it considered too much time wise?

the column is a DB-5 530um 1um film thickness.

Restek doesn't recommend that long.

http://blog.restek.com/?p=10867

It could be a CYA there. I would say that if you're going to go overnight, you might go 20-30 °C below the max. That's still pretty warm for keeping things moving in there. I have done that before without a problem.

Is it a flame detector - or at least some detector that you can watch what's happening on the computer screen? If not, perhaps you'd consider installing it on a GC where you can truly monitor what's coming out of the column in real time. If I really wanted to get to the max, I'd run it up in the morning and hold it for an hour or 2 while watching what's coming out on the computer display. That way, if something goes awry, you can decrease the oven temperature quickly.

If you want to do these drastic bakeouts then you must be completely sure that your carrier gas is free of oxygen and water and your system is free of leaks.

Peter

These extended bake outs are often attempted in order to reduce baseline rise. I find that several short runs near the max temp, injecting 2 or 3 ul of solvent at a 1 to 5 or 10 split, tends to work as well without letting the column sit at max temp for hours.

Ok thanks for the replies. So leaving the column at max temperature overnight would be overkill and will increase degradation of the stationary phase.

Is my understanding of the term isothermal meaning that it can be left at that temperature for extended periods of time without significant bleed?

Isothermal is usually used to mean that the oven/column temperature is constant DURING an analysis. This is commonly done with the very lightest analytes, such as methane or air gases. Unless the context clearly indicates otherwise, I would not assume that isothermal means anything about bleed after extended periods.

Ok thanks for the replies. So leaving the column at max temperature overnight would be overkill and will increase degradation of the stationary phase.

Is my understanding of the term isothermal meaning that it can be left at that temperature for extended periods of time without significant bleed?

A rising baseline can just as well be heavy crud form previous injections eluting as overlapped bands, rather than column bleed. Bleed is a symptom of stationary phase degradation from the effects of high temperatures and oxygen or water in the carrier gas, the more serious problem is degradation of column performance in terms of selectivity and separation.

The maximum isothermal temperature is a compromise - the longer you keep the column at high temperatures the shorter it life will be.

Peter

Hi all,
Can I apply column baking when the MS is joined to the GC and without venting the MS vacuum?
And how?