Chromatography Forum

We're running Agilent 6890s and 7890s, and are supposed to put them in a maintenance method before changing the liner and septum. I have always done GC maintenance while the GC is hot, to save time by not having to wait for it to heat back up in order to tune and load new samples on. Is there any harm to the GC from opening the inlet while it's still up to temperature?

If there is, could someone explain why? Likewise, if there isn't a problem, could some also explain why no harm is made to the system?

Heat, air and polymers are a bad mix. You get degraded polymers - and the stationary phase in a GC column is a polymer. The only question is how much degredation. I have changed liners hot and cold and never particularly noticed a difference, but I am sure that there is some method or set of methods where the air exposure to a column has noticible adverse effects on results.

I usually change septa with the inlet hot, and liners with the inlet cold. I leave the carrier gas running to reduce ingress of air. The oven must be cool of course. How long does it take to heat an Agilent inlet ? - and can't this be incorporated into the blank run that you do after inlet maintenance to ensure that the system is clean ?

Peter

With the people I work with it seems to come down to personal preference. I have never seen an issue with changing liners when hot and have always done it this way. A few precautions are required. Turn the oven down or off, I leave the door open as a double check and don't shut it for a few minutes after fitting the new liner to allow the air in the system to be purged out by the carrier. Obviously there are safety concerns but who hasn't burnt themselves on some part of a GC?

Being a 5890/6890 user I find it an advantage to allow the liner to come up to temperature in the inlet before tightening down the nut. This allows the liner to expand to its working length and rduces the risk of it breaking in the port.

GCguy

yeah everyone here is pretty much correct. its better to change a liner cold, you dont want heat and oxygen creating activity on the liner. if you have the oven cool and continue the flow of carrier its probably not a big deal.

if its S/SL i put the inlet in split mode once i've closed it back up, and set a high split flow for a few minutes.

I've always changed them hot. I'm not convinced that much oxygen gets into the column in the 30 seconds that it takes to change these. I could be wrong.

i always change them hot, i find it easy to simply remove the column from the inlet (with graphitised vespel ferrules the column goes back to where it should nice and easily) and simply plug the end with an old septa. obviously you need to be careful not to block the column but i find it quick and easy, can change a liner in less than 5 minutes. btw i do trace analysis and even do this on our GC-MS and have never had a problem.