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.

  • Try loading the last tune that was hitting targets and tuning off that. Also check that tune wizard is set for the abundances you want. Dumb stuff, but I've seen it happen.

  • Sorry, already tried both of those to no avail. Probably should also go ahead and mention pre-emptively that I've made sure the ion focus and entrance lens wires aren't crossed.

  • Please run a regular Autotune and an Extractor tune and post those reports.  The detuning that happens with a DFTPP tune makes it not that useful for troubleshooting.

  • They look quite good, especially with the ion source at 300 C and transferline at 320, which always reduces the 502 relative abundances, and column flow 1.5, which changes the spectral tilt as well. 

    How many samples have been run on this system since it was installed?  As systems age, this one was installed about March 2019, the total amount of accumulated adhered organic layer inside the entire vacuum chamber builds up and can dirty an ion source quickly. I've seen systems that would make a source dirty in less than an hour or two.  

    The DFTPP and BFB tuning algorithms are not perfect, for sure. They are handy tools, but starting from an Autotune and using lens ramps to manually adjust lens parameters is also valid.

  • Thanks for the feedback. 

    We have got a working calibration on this instrument and are running samples. That said, I am still curious why it would suddenly go from hitting the 55% target to unable to hit it, and why the ion focus lens started giving that S shaped ramp. Nothing about the source temps or column flow changed. 

    The system was installed in 2019 and then sat mostly idle until 2021, as we originally purchased it for an analysis we ended up not having much demand for. I would guestimate the number of samples run since then to be in the 5k to 10k range. 

    From what you said about an adhering organic layer, should wiping down the interior of the vacuum chamber be part of the mass spec's maintenance?

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