Repeller Voltage @ 35V after source cleaning

I just cleaned my source (5977B Extractor source) using the documented Agilent method (Alumina, DIW, Methanol, Hexanes-no acetone step our lab does not have LCMS grade acetone so I skipped it). I spent a lot of time carefully cleaning the repeller (no circular motions, only back and forth on the bottom surface etc.)

The voltage had been hovering around 30-35V for a while and it's been about 6 months since we have cleaned the source (we have a very clean matrix so it's not a huge issue). I was under the assumption that the repeller voltage should drop after a cleaning.

  • Repeller 30-35 is not a typical extractor source tune value, that's an autotune value not using the extractor lens.

    Did you replace the filament?  Have the repeller insulators and the extractor insulator been replaced?  The extractor lens insulator is right there in the ionization chamber area and gets contaminated over time. It doesn't need to be replaced every cleaning and less with clean matrix, but still needs to be replaced sometimes.  Did you clean every surface of all the source parts - inside, outside, every nook, cranny, edge, face?   

    If the tune results are acceptable, I don't worry too much about the voltages.  In Tune, you can look at the tune history report and see the trends, which is often helpful in figuring out what's happening inside.

    And can you share a tune report?

  • FYI this MSD is only 8 months old. One  It's the first cleaning since we have acquired it. The tune history report seems pretty stable for all criteria. The first autotune had a repeller voltage of 28.

    I've been working on Aglient GCs for over 10 years and have cleaned dozens of ion sources but this is my first extractor source. One filament was on it's last legs and was replaced. Both brand new. Our service rep mentioned multiple times that repeller voltage and gain factor is a good indicator of when to clean. A gain factor between 0.3-0.5 and repeller voltage above either 30 or 40?

    I'm new at this company. They typically have cleaned the sources for the previous MS was cleaned only every 6 months.

  • Nice looking autotune, maybe nearly too nice!  ~20% 502 very high, for sure.  Is the column installed directly into the MS and there's 1.0 ml/min going into the MS or is the flow lower due to a splitter?  If the flow is very low or very high, the tune can look wonky.   Is there a reason you're using atune.u instead of etune.u -- the extractor tune using the extractor source?   Running etune will increase your sensitivity, although you may not need it.   The benefit would be that you could reduce the amount injected which reduces inlet and column maintenance and source cleaning.  

    The system is very new. You run a low residue/clean matrix. There are only 105 peaks in the spectrum which is quite low, really clean.  The EM is only 881.2 V, which is barely turned on for an EM as it requires voltage to work.   The 105 peaks could also be a result of the very low EMV.

    Here's my informed guess.  Autotune tries to tune for maximum 502 and your system has a lot of it.  Tune needs the abundance to be within a range but also has to balance the EMV and gain curve, too.   I think that this system is one of the very hot ones that is also extra clean and as the tune algorithm tries to manage it, some of the voltages are different than you're used to seeing.  I bet that increasing the EM one 12V step results in too much abundance and this is the balance that it finds when it's done.  The gain curve can be weird when it's new.  It can be nearly flat.

    So - you can ignore it and run or you can 'burn it in' to reduce the effect of a brand-new EM.  The EM lifetime curve of time vs abundance is a bit like this....not to scale, of course.

    This system is down there in the steep part at the beginning.  If you go into manual tune, setup the system to repeat profile on 28, 28, 28, with the PFTBA off and the filament on, then leave it sit for, oh, a very long coffee break or a lunch break, some even do this for some hours or longer, and then tune, and run, it might result in a slightly higher EM setting in the 950V to 1000V range, still very low, and help out with the way the tune algorithm is tuning.

    As I typed before, I'm not too worried about the tune voltage values if the results of tune look OK - and this tune report looks good.

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