5977B possible lens issues?

After ion source cleaning, this 5977B (inert extractor source) is no longer hitting relative abundance targets during DFTPP target tuning. Should be hitting about 55% for mass 219, but only giving 40-45%. While other ramps seem normal to me, ion focus lens gives the following ramp:

At this point, I have tried replacing all insulators, as well as replacing the entire source (we keep enough new spare parts to assemble an entire unit). No change, ramp still looks odd and tuning is still unable to hit targets. 

I tried running a calibration, had trouble with low response factors with some compounds at the low end of my curve - namely benzo[a]pyrene and a couple of phthalates. I actually wonder if these low responses may be unrelated to the tuning issue, but I would appreciate another perspective on it.

  • The individual lens ramps are good troubleshooting tools but are not always precise. There's a lot going on inside.  Historically, as systems improved and 219/502 relative abundances increased, detuning to meet BFB/DFTPP criteria has gotten more difficult.  It might be easier to meet with a dirty source!    I would try turning down the repeller to, oh, 20V or so, and then ramp the ion focus.  The IF ramps will be different.

    When it sat idle, was it pumped down and helium connected?

    The autotune shows that there is nothing wrong with the hardware/software.

    Wiping down the vacuum chamber is a remedial cleaning step that is sample and throughput dependent. Once every few years or so is reasonable for most.  Use acetone on a lint-free cloth. It will always come out discolored as the manifold is aluminum and dislodging the aluminum oxide on the surface happens every time.  

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