AutoTune vs Tune Evaluation

Good afternoon everyone,

I have a doubt about AutoTune and Tune Evaluation.

I had read somewhere that calibration curves had to be redone as soon as an AutoTune was performed. Therefore I believed that if I would only check the tune with a Tune Evaluation, I would not lose the detector's parameters as long as everything was OK in the report. If not, I would do an AutoTune.

Tune Evaluation reports have been OK for the last 6 months but I recently discovered the MSD sensitivity had dropped drastically, by injecting the same GROB mix injected 6 months ago.

So I believe a Tune Evaluation does not check for abundance. After doing an AutoTune, the EM Voltage passed from 1053 to 1241 and sensitivity improved.

All this because I suddenly lost peaks in the middle of a chromatogram for the same sample.

Is there a way to maintain the MSD response constant over time without doing new calibration curves?

Thank you.

  • If you read the tune evaluation it never references raw counts, just if it can see specific masses and a couple ratio comparisons. I would check with your QA team to see where they stand, but you can also restore sensitivity using gain factor or manual tuning.

    Gain factor wasn't available on 5973 systems and older but you can find it in instrument control under mass spec settings. Let's say your instrument calibrated with a gain factor of 2.5 and an average internal standard response of 600k. Since calibration your IS has dropped to 438k, or 73%. Take your gain factor and divide by your recovery (2.5/0.73=~3.4) for your new gain factor and save the method changes.

    If you run an older system or just prefer manual tuning open up the PDF of your last tune and see what your 69 count was at. Go into tune and vac control and open up manual tune. Open up your PFTBA valve and use the little EMV slider on the bottom of the window until the counts are close to what they were in the original tune and save the new tune file. Depending on the filament your counts can bounce around a lot over a 15 minute period so I use gain factor whenever possible.

    If all you're performing is a tune check this should get you where you need to be. If you're also evaluating BFB or DFTPP adjusting your multiplier can knock your ratios out of balance, for more info on adjusting specific ions Mark Ferry wrote some great articles on it.

    Best of luck,

  • The tune evaluation was written for an orthogonal ion source (SS/Inert/Extractor) system, atune or etune, running helium carrier gas between 0.8 and 1.4 ml/min, at 230° C ion source and 150° C quad temperatures. It may not pass using other temperatures, flows, hydrogen carrier gas or the HES and yet the system is fully functional and there is nothing to repair. It is not for Stune, BFB_tune, DFTPP_tune, target tuning, and not designed to be used for PCI or NCI, either.

    The tune algorithm can change every parameter, so the overall response will be different after tuning. That may or may not be an issue depending on how you run your system, though.

    See the blog article    (+) Agilent Community    Don't Tune So Often !

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