Huge contamination with m/z 251.9 and 483.9 on GC-7200QTOF

I have a huge contamination in my MS (GC-7200QTOF system). I see the peaks (251.9, 483.9) when turning on the filament and also during GC-runs (less with higher temperatures). My predecessor recalled seeing the same problem 6 years ago and that it was due to an oxidized filament. Changing filament and cleaning the source have helped back then. 

So far I have changed liner and cutting parts of the column, this didn't help, backout of the source neither. Carrier gas can be excluded, the other GC-MS on the same gas supply don't have that contamination. We have an oil-free foreline pump. 

Can someone confirm that this is the filament? How can this be prevented from happening again?

  • We have taken out the source, cleaned the source and replaced both filaments. It is still pumping down but a first climps indicates that the contamination is not gone yet. Ion distribution has shifted a bit though. Any more ideas?


  • That is rhenium oxide from the filaments.  You need to take it apart, clean it all again, replace the insulators and both filaments.  This happens when the filament is damaged from an air leak. Clean everything well - all the surfaces of the source inside and outside, every hole, nook, cranny, surface, face, edge. On a 7200 you may even need to vent and wipe the source radiator with a solvent-dampened lint-free cloth depending on how bad it is.  This spectrum is from August 2015.


  • Ok, thanks for confirming. We will repeat the cleaning procedure tomorrow (and clean more thoroughly then). 

  • After a 2nd set of thorough cleaning, we have managed to get rid of all the rhenium oxide. Here a quick sum-up of what we did:

    1. abrasive cleaning (Alox/soap/water) of those parts that can be abrasively cleaned followed a ultrasonication (tap water, deionised water, acetone, methanol, dichloromethane)

    2. ultrasonication of all other metallic parts (except isolators and heater) (soap/tap water, deionised water, acetone, methanol, dichloromethane)

    3. isolators (and knob) cleaned with a methanol-dampened cotton swab

    4. wiped source radiator in and out and ceramic piece on transfer line with methanol-dampened lint-free cloth (Kim Wipe)

    The system is up and running again. Obviously, this big manipulation inside the source brought in some contamination, but I am confident that this will resolve with time. (with more injections and probably with another bakeout)

  • Thanks for the update!  Some don't like the use of soap. I think that it depends on the soap used and how well it is rinsed afterwards. There are soaps that leave a residue that is hard to remove, or at least not easy to remove.

    Kim Wipes are low-lint, but not lint-free. I like the lint-free cloths as supplied with the system.  Lint residue in the MS can be seen as noise. This is especially true on SQ/TQ systems at the HED and EM.  -10,000V excites any particulates and results in noise.

    For source cleaning recommendations, check out the videos here: Eliminate the Fear of Mass Spec

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