6890N GCMS with Poor Tune

Hi GCTime thanks for participating in the Community!

I moved your question to the GC/MS Forum for better visibility.

Cheers,

Kristen

Does this MS have a turbomolecular or diffusion high vacuum pump?  When was the last full preventive maintenance performed?  When was the last time that the electron multiplier was replaced?

What column is installed?  The injection port pressure works properly if it is always higher than 5 psi.  You say it is less than 1 psi ?  There is probably so much air inside that it cannot finish. If the inlet pressure and the total flow is too low, air can be sucked backwards into the inlet, the column, and into the MS.  Try pulling the column out of the injection port and capping it off. The easiest way to do that is to carefully press the end into the edge of a septum until it is stuck.  Wait five or ten minutes and then try tuning again. With no flow the tune won't be perfect but it should be better than before.

It is an AX-65 diffusion pump. The fluid level is fine. 

The EMV has never been replaced. Aside from the cleaning and routine maintenance and replacing the EI I mentioned, nothing else has been done. 

I checked the autotune values and the EM values were in range; the last one was 1482.

The column is an Agilent DB-1, 122-1062. I changed the inlet pressure to 5 psi and used the septum trick. The tune was better, but returned to having problems when I tried to tune it with the line in the inlet. Th e first image is the tune. The second is from the failed tune.

Maxed out 28...a huge air leak.  Vent, replace the column ferrule with the proper graphite/vespel one, wipe off or replace the analyzer O ring, cap off the column again, pump down and try it. If the leak isn't fixed you can't figure out any other problems.

The very ugly tune ion peak shape is probably related to the air leak but won't know until the leak is fixed.