Chromatography Forum

I have another 5972 that has always plagued the operator with high 44 background, that will recede after several days of pumping down. I am fairly convinced this is not a leak (carbon dioxide), as we do not see associated 28, 32, or 40 ions. We do not see this on other instruments on the same gas line, so I doubt it is the tank.

This is a diffusion pump system. I do not believed 44 is associated with the pump fluid? I know it has not been changed in years, so I am trying to talk myself into it.

Any ideas?

I have another 5972 that has always plagued the operator with high 44 background, that will recede after several days of pumping down. I am fairly convinced this is not a leak (carbon dioxide), as we do not see associated 28, 32, or 40 ions. We do not see this on other instruments on the same gas line, so I doubt it is the tank.

This is a diffusion pump system. I do not believed 44 is associated with the pump fluid? I know it has not been changed in years, so I am trying to talk myself into it.

Any ideas?

Could be the old oil has some carbon built up in it and every time you cool and vent it absorbs some CO2, then bakes out after a few days. Good time to change the oil, and do a good cleaning on the components of the diff stack while you are in there.

Thanks James. I may replace the pump fluid next time I can afford to take that instrument down.

This is a common problem with graphite ferrules. Never completely understood why, but we would see 44 (CO2) if we overtightened the graphite ferrule at the MS interface. Switched to aluminum ferrules and all of the problem went away.

This is a common problem with graphite ferrules. Never completely understood why, but we would see 44 (CO2) if we overtightened the graphite ferrule at the MS interface. Switched to aluminum ferrules and all of the problem went away.

Interesting. Are you referring to these ferrules (Link)? I haven't tried them. Do they perform as promised, e.g no re-tightening, more leak-free?

Do they perform as promised, e.g no re-tightening, more leak-free?

Yes they do. We use them to connect retention-gap and analytical column and that works perfect.
Have not yet tried to use them for a transferline.