For some time now we’ve been experiencing a phenomenon which we can’t put our finger on. We run multiple agilent 7000C. When installing a fresh ion source we get a tune spectrum that is off from what we expect, it looks as follows:
Note the very low m/z 69.
We expect a spectrum that looks like this from a fresh source tuned using m/z 264:
When manually tuning the only thing I can find that’s not “normal” is the repeller ramp. The ramp for the PFTBA ion profile looks like this:
What seems off is the apexes are quite spread and especially the apex for 69 is way high. A normal repeller ramp 0-20 would leave 69 without an apex at all. When ramping the repeller on another system it looks like this where the apexes are tighter, and none are over 20:
We have had some issues with repeatability that has been linked to this. Correcting the repeller settings to produce an expected spectrum resolves it. Anyone have any good idea as to why this is happening?
As far as I know this happens with new, freshly cleaned repellers. Is there something I’m missing?