Why are air blanks OK?

[Masspecs]

I've always been told that oxygen is terrible for column life; however, I've also been told that air blanks are adequate measures for clearing a column out. Which is correct?

[Bigbear]

Don't know what you mean by "air blanks". I time a non retained compound using air. I do this check at 40 C and only inject 1ul. The problem with O2 is if the oven hotter than 100C and there is lots of air ( like a leak).

[Peter Apps]

I've always been told that oxygen is terrible for column life; however, I've also been told that air blanks are adequate measures for clearing a column out. Which is correct?

Oxygen and moisture are bad for columns so you don't want to be repeatedly injecting air. Even less do you want oxygen and moisture in the carrier gas.

I can imagine that the myth of injecting air to clear a column out is based on the big hump of degraded stationary phase that you get when you inject significant volumes of air at high temperatures - that certainly looks as if it is muck being cleared off the column but in fact it is the sign that you are destroying the column even faster.

Peter

[GOM]

As Peter pointed out, air(oxygen) and moisture are generally bad for columns.

Bigbear hit the nail on the head with what exactly do you mean by air blanks? Is this a headspace analysis?

Yes, sometimes a blank run may be required to "clear" the column and inlet from residual higher boiling analytes from the previous injection

As always, much more detail on your analysis and conditions would be so helpful

[Masspecs]

delete

[Masspecs]

Don't know what you mean by "air blanks". I time a non retained compound using air. I do this check at 40 C and only inject 1ul. The problem with O2 is if the oven hotter than 100C and there is lots of air ( like a leak).

When I say "air blank," I mean a gc vial with absolutely nothing in it but the air. This aliquot of air is injected onto the column as a "blank."

[Peter Apps]

Don't know what you mean by "air blanks". I time a non retained compound using air. I do this check at 40 C and only inject 1ul. The problem with O2 is if the oven hotter than 100C and there is lots of air ( like a leak).

When I say "air blank," I mean a gc vial with absolutely nothing in it but the air. This aliquot of air is injected onto the column as a "blank."

Why not just run the oven temperature programme ?

Peter

[James_Ball]

Agree with Peter, it is easier to just hit the start button with the method loaded and let it run through an oven cycle without injecting anything at all, or load in whatever solvent you are normally injecting and let it shoot a solvent blank. Air blanks will do nothing good for the instrument and will give no useful information unless you are doing air samples to look at the ratio of N2:O2:Ar:H2O or something like that.