Chromatography Forum

Hi,

Someone in our lab changed the coulmn without venting and pumping down GC/MS. Now, the foreline pressure is 4670 mtorr (very high) and it is oscillating with numbers 4656, 4668 etc.,

When we tried to pump down after venting, it is not pumping down (5 hours). What should we do? Is our MS dead?!

Please help me.

Thanks
Thary

with out knowing the make and model of your system it could be that exchanging column without venting the MS it might have reached a vacuum level that causes it to go into an error state.. It will most likely not recover from this state without a complete shut down (with a venting) and turning it back on..

Also double check the ferrule used to connect the column to verify it is the correct sized ferrule for the mounted colomn..

This advice would be good for an Agilent MS, but probably works for other vendors.

Turn it off, vent, examine vacuum chamber for oil and also check oil level and condition in rough pump. Check the O-ring the door sits against to make sure it is evenly inserted and not kinked. Remove column and cap off MSD with blank nut, checking threads of the transferline to make sure there is not a massive leak there. With no column installed it should pump down quickly.

Once capped off and ready to try and turn it back on make sure the door to the vacuum chamber is sitting evenly against the rest of the instrument and hold it there to make sure you get a nice seal. Turn it on and see.

Is this a turbo or diffusion pump system?

Sounds like you have a large leak on a diffusion pump. Make sure you have oil in rough pump and the right level of oil in your diff pump. I would guess that the leak is at the analyzer tub / chamber. Make sure the side door or top (depending on which MS you have) is seated and pressed on the o-ring while turning on the vacuum. Other likely place would be the column nut / ferrule.