GC-MS Detector Gain Calibration test in Autotune Failed

[Carvone]

Hello all,

I am experienced working with GC-FID but relatively new with GC-MS. We work on a Thermo Ultra Trace GC-MS, and recently it failed the gain calibration test in autotune. All other tests RF dip calibration, leak check, and mass calibration all passed.

I spoke to the Thermo rep, and he suggested cleaning the ion volume, the ion source and lenses, which I did using aluminum oxide and glycerol and later sonicated with acetone after washing. I reinstalled them and then used dry nitrogen stream to gently blow clean the prefilter, quadrapole and detector.

Detector Gain is set for 1x10e-05 with the multiplier running at 1200V (the manual says to replace multiplier when it is at 2500V) so it is not worn by far. The vacuum was very low at about 30 mTorr, it was checked for leaks and passed. The Electron multiplier is only about six months old, and there was a new filter for the helium installed at the same time.

If anyone can offer any insight into how to further troubleshoot this problem, I would be most grateful.

Thanks-- Carvone

[WK]

Hi Carvone,
With a name like that I can guess you work in essential oils?!
What condition are your filaments in?
Can you swap to use the other one?
Regards
WK

[Carvone]

Thanks WK for your response. Yes, I used to work with flavours and I thought carvone was the compound that best described me (bit of split personality!).

I forgot to mention the filament is new as well replaced a few months ago. I only have one other filament right now and that is the earlier (much dirtier) filament, so I do not want to put that back in. When I cleaned the ion volume, ion source and lenses, I looked at the filament and it looked clean with only a small black mark around the hole where the electron beam goes through from rhenium wire into ion volume ionization area.

What does this suggest? Thanks.

[willnatalie]

If you simply scan, are not seeing air peaks or "ghost" peaks?

Was the column replaced
If so how far the column is placed could affect the situation, and if the nut for the transfer line was over tightened this could be an issue (very low pressure would be seen in the MSD).

Is N2 you carrier gas? You could be swamping your detector with N2, Try using He instead N2.

WillNatalie