Chromatography Forum

Hello everyone,

I am currently troubleshooting a massive air leak in my Agilent 5975 Series MSD. When checking the manual tune menu, the abundances are extremely high: >500% for nitrogen (m/z 28) and >100% for oxygen (m/z 32), relative to mass 69.

Interestingly, the system seems to pump down without any issues. The turbo pump comes up to 100% speed within 5 minutes of pumping down, and the pressure rapidly reaches e-07 Torr.

To isolate the MSD, I disconnected the chromatography column and installed a blanking nut directly on the MSD transfer line. Unfortunately, the leak persists.

The background is currently so high that I am unwilling to leave the source filaments on for any extended period. Because of this, I am unable to safely use compressed air or argon to leak-test specific connections.

Maintenance and troubleshooting attempted so far (none have resolved the issue):
> Tightening the blanking nut.
> Using an Agilent-recommended rethreading tool to remove any brass shavings from the MSD transfer threads and ensure proper alignment.
> Checking the PFTBA level (it is adequate).
> Replacing the O-rings at the PFTBA mount and the vent valve. And wiping the connecting down with ethanol.
> Cleaning and inspecting the large main MSD chamber O-ring with ethanol before pumping the system back down. (have not taken the o-ring out for a complete wipe down)

One other symptom I have noticed is that the leak is substantially worse when the transfer line heater is off --> so I am suspecting the issue might be in the transfer line weldment or a failing seal at the transfer line interface, where thermal expansion helps temporarily seal the gap.

Has anyone experienced a leak of this magnitude on a 5975 where the vacuum still comes up so quickly? I would especially appreciate any advice on what to check next or how to track down a leak this large without risking damage to the filaments.

Thank you in advance for your help!

The leaks I have experienced have either been very low and a slightly loose fitting which is fixed with a tightening of a nut or so large the chamber door doesn't stay. My first thought was that there is a minor spec on the chamber O-ring, but you mentioned cleaning it so I doubt it is there.

You mentioned that the transfer line heater off makes the leak worse, so I agree that there is something there. Could you plug the end into the MS, instead of the GC side? I am wondering if that would "fix" the leak and isolate it into the transfer line. I don't have one in front of me so I'm not sure if there is a weld somewhere else associated with it that my suggestion wouldn't help.

Try spraying methanol on any welds/areas you are suspicious of while watching the vacuum gauge. Liquid methanol will get sucked in to any leak, then make the vacuum worse as it evaporates into the MSD.