Tune spectrum low m/z 69

Hi everyone,

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?

  • Autotune is a dance with many partners.

    The ionization of PFTBA is affected by column flow rate, column tip location, carrier gas type, filament age, filament alignment, electron beam hole cleanliness, electron energy, filament current, ionization chamber cleanliness, and more.

    The spectral tilt, the relative abundances of the fragments, is affected by repeller cleanliness, repeller flatness, repeller alignment, repeller insulator cleanliness, ionization chamber cleanliness, extractor lens cleanliness, extractor lens flatness, extractor insulator cleanliness, extractor hole cleanliness, ion focus, entrance lens, quad 1 transmission efficiency, collision cell gas flows, collision cell transmission efficiency, quad 2 transmission efficiency, iris, HED cleanliness, electron multiplier gain, electron multiplier age, vacuum level, air/water level, how many and what type of samples have been run on the system in the past, and on and on.... 

    Does this happen on only one 7000C?  Only one set of ion source components?  Are you waiting at least one hour and preferably two or more after pumping down before testing/tuning for the vacuum to be good enough and the temperatures to be stable?  What source/quad(s) temperatures, column flow rate, CC flows, etc?  Can you share the tune reports?   

    One easy thing to try is to -not- tune it, just do "Generate Report" after you install the clean source. That does not change any parameters, it just opens the PFTBA valve and acquires new tune ion peaks and the spectrum.  What does the spectrum, the tune ion relative abundances, look like before and after cleaning if you don't tune?

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