Chromatography Forum

I have a newer Agilent 6890 GC w/ 5975 MSD. I seem to have a chronic
air leak primarily with high N2 (28) >15% abundance. O2 (32) isn't bad @ ~3.5 to 6% . I was reviewing my tune files going back about 6 months and it seems constantly hi 28 despite changing columns and performing regular inlet maintenance (new merlin microseal, change inlet liner and o-ring). Inlet has flip top assembly. Any thoughts?

Tighten (slightly) the transfer line nut in the column oven. Sil-tite ferrules seem to eliminate the need to re-tighten this periodically.

Lower response of O2 doesn't mean O2 is better than N2, actually it's as bad as N2. When you have an air leak, response ratio od N2 to O2 should be around 3 to 1. The ratio is one sisn of air leak.

To locate the leak, you want to isolate the problem first. Disconnect the column from the injector port, seal it with septum, wait for 5 mins and ckeck for m/z 28 and 32. If the responses are still the same, the leak is in the downstream of the column. If m/z 28 and 32 go away, the leak is in the upstream of column.

Are you running in split or splitless mode? we had one problem where 28 and 32 where high (> 20%). we ran in splitless mode and we spent hours and hours trying to troubleshoot the problem. we finally found the problem. it was the Auto pre run setting on the GC. it was ON, which for some strange reason allows air in when running in splitless mode. after we turned it off, all was good.

To get there, on the QC control pad, click "config", "instrument" and you should then see the auto prep run setting. just make sure it's turned off.


now i don't know exactly what that setting does, so make sure your method still runs okay before hitting 'start' and walking away

hope that fixes it.

Hi!
Simply, scan mass 40 and use ''Argon '' to check all connection like MS gasket, interface connection ect....

Hi again!
It is not impossible that your problem is gas tank.......