Chromatography Forum

Mass 219 with very low abundance after two electron multipliers, two ion source changes. One feedthrough board change. Negative polarity results in a slight increase but not acceptable abundance. Slow slide to low abundance from about 80 during a five day period. Water is showing up but the instrument has been pumped down for over a day. I would expect it just after pump down, within an hour or so. Very little air is entering.
Any ideas would be appreciated.

How old are the traps on the gas line and have you tried replacing them yet?

Are the profiles of the lens "normal"? If you have a before and after it may give a bit of insight on what's going on inside.

Greg

Is that tune a day after pumping? If so, the water seems a bit high still. Also the repeller voltage is a little high as well. With a clean source, it should be more like 25-29 volts.

MS QUAD temp. 200 => 150
Filament 1 => 2

MassGain, Repeller (V), (Entoffs-Entlens) - high + EMvolts, ionFocus - normal =>


Vacuum chamber dirty, dirty ion sourse, electronic problem (check control point's), dirty HED, dirty gas

Thank you everyone for the input. I will find out more on Monday when I go in to work. I isolated the mass spec. and as of Friday afternoon, last week, mass 18 was a bit high with no input from the GC side.
I noticed someone trimmed the analytical column twice right after install the previous week, right after I installed a clean ion source and multiplier. I think there's contamination. I plan on cleaning things on Monday. I didn't see any real variation in Ion Focus, Entrance Lens etc. over the past month looking at past tunes.

I have two other mass specs on this same helium line and have no problem with mass 18 or any tuning problems.

A polaity change from positive to negative helped a bit. 219 around 50 relative to 69. Better than 20 with positive polarity. I'm still uncertain for the change and will wait to see if some part fails and is obvious or 219 takes a plunge again.

This is a long shot, but how much PFTBA is in the vial? I have seen strange results when the level gets low.

The level was good but I emptied the vial and replaced it with new PFTBA straight from the ampule. Tune is about 35 for 219. No improvement.

BCBC,

Have you looked at dipping the quads? I have done it a couple of times in my career and it helped in both cases but it is not a common solution.

The other thing I would recommend if you can do it is to swap the analyzers. Not having my own 5973 in front of me, I am not sure how you would do this but I suspect you could do it at the hinge.

This would provide insight into support electronics or components on the side board.

By the way, is the water gone?

Best regards.

Thanks for the advice. I dipped the quads a few days ago and no improvement. I may be able to swap an analyzer from another machine. If not that, replace a few boards starting with the side.

No water now.

For "virtu" I haven't cleaned anything yet. I may just go with cleaning the HED, quad and vacuum chamber to start. Thanks.

BCBC,
What fixed the low 219 abundance? We are having the exact same problem.
Thanks!

I will check the maintenance book monday to see what ever became of this problem.