Mass Spec leak - Chromatography Forum

Mass Spec leak

Discussions about GC and other "gas phase" separation techniques.

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Hi, I'm struggle to use my GC MS system due to a leak. I had to change my column to a HP-Innowax and from here the problem started.
I cleaned the EI source, changed the ferrules, changed the MS nut, Inlet Liner, Septum, o-ring, Gold Seal but still didn't solved my problem.Actually made it worst. Firstly my amount of water and air in the system was huge, now I go weird tuning and air level doesn't drop down (file:///C:/Users/LUMINI~1/AppData/Local/Temp/20180809113849653.pdf)

We have a GC/MS- HP 6890 series with a 5973 Network Mass Selective Det

Does anyone has any idea what else I should check? replace?
Thank you
Lumi
Lumi Moraru
Analytical Chemist
MET
Have you checked for leaks at the door on the MS? I use Dust-Off or equivalent.
As the previous reply suggested try canned air or something similar on the MS and monitor for the right ion from the canned air chemical. Also try the same tests on the GC fittings including the inlet. Don’t forget to try the fittings between the gas cylinder and the inlet
If that doesn’t work try lowering the temperature of the oven and see if the levels go up. If that happens then the leak is in the GC oven fittings.

Kevin
Before I close it up and start pumping down, I have taken to applying a very thin (I mean really thin) Apiezon Grease to that gasket in the door. I find I have a lot less trouble getting a good seal that way. I use the "L" type.

http://www.apiezon.com
I agree with Steve/soccer and advice to first locate the leak before doing random maintenance. I can add that an electronic leak detector is not a luxury if you're doing GCMS. The trick with the spray can is great the closer you're looking for leaks around the MS, not so much at the inlet or gas fittings before the GC.
Hi, thank you everyone.
I have checked for leaks using the spray can but nothing shows up, I can't find any leaks. Now I've just realized that the calibrant vial needs to be filled, it might be that the reason for my weird tuning? waiting for it to be delivered and see how that will change.
Thank you
Lumi Moraru
Analytical Chemist
MET
It looks like your link is pointing to a drive that is local to your computer. You'll need to upload the pdf to site that will allow you to share it with us.
Lumi wrote:
Hi, thank you everyone.
I have checked for leaks using the spray can but nothing shows up, I can't find any leaks. Now I've just realized that the calibrant vial needs to be filled, it might be that the reason for my weird tuning? waiting for it to be delivered and see how that will change.
Thank you


If the m/z 69 was low because of low calibrant gas, then it would make the air and water look exaggerated. When first evaluating an instrument after major maintenance I normally scan with the cal valve closed and look to see if m/z 18 and 28 are low or falling. With everything sealed up they should be below 100,000 counts, if they are in the millions of counts then either there is a leak or it just hasn't pumped out yet.

The ferrule on the column inlet at the MS interface can also shrink after it has been heated for a while and needs to be retightened a little sometimes. If the leak is less when the oven temperature is high, that is the most likely place for a leak.
The past is there to guide us into the future, not to dwell in.
Just as a thought, are you sure you used the correct size(ID) of ferrule at the transfer line fitting? Of course, both should be sized correctly, but the one at the transfer line can cause headaches if it's not.

Also, someone else mentioned greasing the gasket on the door. I have put a THIN smear Dow-Corning high-vac grease here before, but it's more important that it be clean. I usually use a(dry) Kimwipe to wipe both the gasket and mating surface down before I start pumping down.

This one is a shot in the dark, but don't forget also that the diffusion pump can suck up a lot of junk if the m/s is vented while the pump is still hot. I'd guess that it would take quite a few vent cycles with a hot pump to cause a big problem, but none the less it's there. It MIGHT be worthwhile to change the diffusion pump oil.
Hi everyone, thank you for all your thoughts.
I did changed the PFTBA calibrant(the level of it was very low) and then I did isolated the Mass spec using a blank nut to see if there is anything wrong with it or the leak is coming from the GC unit. The Mass spec tune was OK after the isolation, that encouraged when I've seen that the MS doesn't have any issues. So today I did put my GC column back in the GC using new ferrules and everything came back to normal.yey
My theory is that the fact that the calibrant level in the vial was low ruined my tuning.

Thank you
Lumi
Lumi Moraru
Analytical Chemist
MET
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