Chromatography Forum

Hallo,
Maybe someone had similar problem before. Today I have replaced the ion source in the GC-MS (agilent 5975C,6850) and when i do autotune it shows that the foreline pressure is too high (it shows 74 ). Before the foreline always was about 70 and everything was ok but now I am not able to do water and air check or autotune because it shows that foreline pressure is too high-pressure has exceeded 300mTorr).Column flow is 1.3
I would appreciate any advices what I should do. Anna

Hi again, I have replaced the ion source for the old one which I had cleaned yesterday but unfortunately I get the same error massage: The foreline pressure has exceeded 300mTorr. The system is in VENT state (high vacum pump off). However on the instrument control window foreline pressure is about 59 (which is correct). Anna

Anna,

-Check connections at the back...is the foreline pump cable correctly plug to the instrument?
-Check the MS interface nut see if it's correctly tighten (a leak here can give high pressure and the system does not reach vaccum...)
-Did you try rebooting the system (with computer also)?

Regards,
At_om

Hei hei,

I checked all the possible connection that need be sealed: ion source chamber, union among the GC column and the ion source. I also restarded the system but unfortunately the problem hasn`t dissapered. The foreline pump seems to work ok and all the parameters on the control window are ok (even foreline is about 60 but not 300mTorr as it says during the error massage).Could it be something with the software?

Can you check if your turbo or your diffusion pumps are working?

The turbo should make a characteristic whining (especially when pumping down). If it is a turbo can you reach 100 %? (you can check that on the control panel of the instrument).

If instead is a diffusion pump can you feel if it's hot and if the fan is working?

It might be worth to reboot the controller (using the control panel of the instrument).

Good luck.

hei Yes I ahave checked everything what you recommended and everything seems to work ok. The diffusion pump is hot and fan is working (we do not have a turbo pump). I also rebooted the controller. Do you have any others suggestions what it could be?

Can you see, using the manual tune (or spectrum scan), if you have air in the system?

If everything seems OK maybe you can try to copy another autotune macro (atune.mac I think) and trying again or resetting to defaults?

If foreline pressure does not get low fast enough (within a few minutes) the MS will turn it OFF in order to protect the system. You have to restart the MS in order to get the rough pump to come back on, this is a bigger concern for people with diff pumps because it tends to take a little longer to initially pump down.

Are you putting pressure on the analyzer door when you first turn the MS on? If not you may be leaking some. You said you checked the common leak points, but make sure that the O-ring around the analyzer door is in the correct position. It tends to kink out slightly when the system is vented/door open. With a gloved hand gently apply pressure with your fore finger and make sure it is evenly pressed into position.

Have you changed columns recently? If so you may be leaking from the interface, the ferrule tends to expand/contract a bit as it is heated and you usually need to give it an additional quarter turn once the oven/transfer line is hot. An interface leak isn't usually enough to keep you from pumping down, but a leak at the door definitely will.

Your vent valve on the front of the MS is closed tightly right? When you turn the MS on if you crack it open slightly do you hear a hiss or nothing?

With the system off you may want to completely unscrew that vent knob and make sure the o-ring behind it isn't torn or out of place. It is the same kind of o-ring used on the liner in the inlet, if you need to replace it.

Good luck, leaks suck.

Today I managed to fix GC-MS:-) The reson was a calibration vial which had to be refilled with PFTBA. Anyway thanks a lot for your valuable advices, it was really useful!!

How is this problem related to foreline pressure?

There was air leak-calibration valve (calibration vial was loose).

I had exactly this kind of problem some years ago. The foreline pump pressure was always around 200mmTorr or so, just enough for the dp pump to be turned on. But it cannot tune or analyze. Finally, it is the leak at the calibration valve. It took me 3 days before the error was found.