MS leak- Chemical Ionization mode.

[pdixi001]

Hi...

I have been battling to make my GC-MS work in the CI mode to quantify NitroPAH's. After many trials, finally found the column to be dead, so installed a new column in the hopes of getting good chromatography. But, now after installing the column, the MS has pumped down, but I am not able to get rid of the leaks.
I run a methane Pre-tune and see peaks at 15,17,19,28,30,31,32,40,41,43,44,45,46.
They dont seem to go away. I have cleaned the MS source, checked for any particles (hair, fabric etc..) inside the chamber, grease sealed the side plate, changed the viton-O ring of the vacuum vent valve, tightened the MS interface nut at the GC side, rebuilt the inlet (splitless inlet) at the GC side, checked for leaks in the flow path (upstream from the inlet) for leaks using electronic leak detector (found no leaks there).

Please provide me with some insight so that I have a breakthrough.... this is getting frustrating...

Thanks,
pdixi001.

[Don_Hilton]

What type of instrument are you working with - And, Grease seal? On instrument's I've used a very thin layer of Apeazon H is OK, but too much is worse than none - so how have you made the grease seal? (When I say thin, I am talking about touching a fingertip to the end of the tube of Apeazon, taking only that portion that sticks to the finger with the touch and then spreading that around an entire sealing surface. Having done that, taking a Chemwipeand polishing off the excess. All that you can see of the grease that you added is a shine on the surface. This, techniqe includes something the size of the boot seal of an HP (now Agilent) 5972.)

[pdixi001]

Hi..

I am using a GC 6890 agilent, and a MS with it. I used the apeazon grease. Yes, I cautiously used a very meager amount, after which wiped off with a kim wipe, and only made sure there is a very thin , barely there sort of layer.
Yesterday I changed the o-ring on the side plate (the whole viton ring on the entire surface of the sideplate). The pretune looks way better today. I will run a tune today to see what shows.

thanks,
pdixi001

[Bigbear]

We've had the CI weldment on the transfer line go bad and leak. If you have some "canned air" set the manual tune to scan for the major ions of the canned air and spray it at the transfer portion that is between the gc and ms. Sometimes this is difficult to do.

[James_Ball]

We had a stubborn leak on a 5975 we bought used and finally one day when an analyst was tightening up the nut on the MS column transfer inlet the end broke off. The leak we could not find was a hairline crack in the interface just after the threads.

If you replace the interface be careful when tightening the aluminum crush washer seal for the CI adapter.