Chromatography Forum

I isolated the MSD (5973 with turbo) from the GC to find an air leak.

An air/water check gives me the following.


18/69 = 55.50 % Water

28/69 = 6.75% Nitrogen

32/69 = 2.49 % Oxygen

44/69 = 0.88 % Carbon Dioxide

28/18 = 12.85 % Nitrogen/Water


Any thoughts? I had about 13 % water before I isolated the MSD.
So I know I introduced air with water when I capped the interface but this was about 3.5 hours ago and I'd expect the water % to go down...maybe not it is humid here.

Hi!

Check the seals (vent valve, lateral seal). If OK, check the o-ring of the interface.

Good luck!

Thanks for the information.
I replaced the side door o-ring. have replaced the interface o-ring.
Never had a leak indication in those two places but replaced them anyway.

If the nitrogen is OK (or close to OK), let the instrument pump. Water adsorbs to surfaces and comes free slowly. If you have capped off the MSD, you have no carrier flow to sweep water out of the source. Expect it to clear more slowly.

Thanks for the information.
I'll know more on Monday after a weekend of pumping down.

You should connect the column to the MSD for the carrier gas to sweep out water trace. Anyway, leak (if any) from the interface, inlet (column) can add air and water into the msd.

There are times when it is appropriate to plug off the transfer line to look for a leak. It is a pain because the gas flow conditions have changed. But, it can help to confirm that a leak is in the mass spectrometer.

It is rare when there is a leak in a mass spectomter. Typically is a seal that you have had apart. On ocassion, it is something like a pass-through that has cracked. (A perfect end to a bad day!)

My personal preference for tracking down a leak in the mass spectrometer is to reopen the seals that I have had apart, clean them, and reassemble them (including the seal for the vent!) -- with the exception of copper o-rings. With copper o-rings, if you always use new o-rings and properly torque the bolts, it is next to impossible to fail to seal the joint. If the leak goes away, problem solved.

Monday I had 8 % water, 5% nitrogen and 2 % oxygen.
It looks better. I replaced the ion source as 219 was getting pretty low in abundance an let it pump down for a few hours.
Next check will be on Thursday. I'm off today.
Thanks for the help.

Changing out the PFTBA helped a lot with the water level.
Reconnecting the column with helium flow also swept out water.


This morning I have nitrogen at 2.5 %, Oxygen at 1.36 % and
water at 2.4 %.