Chromatography Forum

So I figured I'd start a new thread since this issue seems unrelated to the previous ones. Anyone that's seen my previous threads, this is the same 6890N/5975C/CombiPAL system I inherited that had been sitting vented in the basement for 8 or so years (thanks to everyone that's helped me out the past year getting this thing up and running).

I've finally managed to get a good looking sample run completed, however in the tune history I've noticed this



Should I be concerned over that large drop in the ion focus value? Is this due to a dirty lens, or something else? For reference, I inherited this thing around the 95th tune mark.

Was the ion focus value at the maximum (often 90V) and now it's something more reasonable?

That's a good question. I assumed since it had been running at ~90V since it was first assembled, that's where it should be, but I guess running at a lower voltage could be a good thing? Am I going to lose low mass sensitivity?

You are also decreasing the 209 abundance.
Unlike my 5973, I find that my 5975C and 5977 both like to have higher ion focus values. I turned the maximum up to 110 V for each. So that while the 5973 is usually around 80V the 5977 runs 90 to 100V.
With your EM voltage rising and 209 dropping it looks like something is changing. Is your repeller voltage increasing too?

Yeah, the repeller voltage is increasing (decreasing?) what looks like proportionally to the ion focus voltage

There can be many combinations of lens voltages that make an acceptable tune. You can reduce one lens while increasing another such as repeller vs ion focus, and achieve the same relative abundances. Also if the Entrance Lens Offset is set to variable, those numbers can affect how the other lenses respond.

Repeller voltage can be manipulated by using different Emission Current settings, one trick is to adjust the Emission Current until the 219 curve peaks near 20v and gives a bell shaped curve, often you can get the Emission Current down in the 20ma range instead of the default that is near 35ma.

I have had lens setting change completely just by cleaning the source and having the lenses aligned slightly different than they were when installed the last time, other times I can go through several cleanings and make almost no adjustments at all to tuning parameters.

If this instrument has been sitting for 8 years, then it must not have been used that much when it was new, since it can't be much over 10 years old I would think, so I wouldn't stress much over the values being different now than what they were back then, so long as you get stability and sensitivity that meets your current requirements.