Etune acceptance criteria

Does anyone know what the acceptance criteria is for an Etune to pass? We are investigating the different tunes on a hydrogen GC-MS.  Thanks!

  • Etune is the extractor ion source tune. The extractor source energizes the ion body and the extractor lens to improve the ion transmission out of the ionization chamber and into the quadrupole. It increases the system sensitivity. Most of the time it changes the spectral tilt, too, so the 219 and 502 tune ion relative abundances compared to 69 are higher than an Atune. 

    Hydrogen in a GCMS ion source works very differently than helium.  It is not a trivial change between gases.  The MS pumping speed for H2 is only about 60% compared to He, so the maximum column flow is much lower. The space-charge effects are different, so the overall sensitivity will be less using H2 than He, as much as an 80% reduction for some compounds.  The ionization chamber pressure due to the number of H2 molecules means that the 9mm extractor lens is recommended, which can also affect the ultimate sensitivity.

     See:  user-guide-coverting-ei-gcms-instruments-5994-2312en-agilent.pdf

    The Tune Evaluation is not specific for the ion source nor the carrier gas.  The Tune Evaluation ranges were written for an orthogonal ion source (SS/Inert/Extractor) system with the 3mm drawout/extractor lens running helium carrier gas at 1.2 ml/min and 230°C ion source temperature. The tune evaluation may not pass using hydrogen carrier gas, 9mm drawout/extractor, higher or lower flows, or higher ion source temperatures, and yet the system is fully functional. Tuning is making sure that the system is somewhere in large range of acceptable functionality.  If a system completes tune with no errors – in nearly all cases, it’s working more than sufficiently fine for nearly all applications.

    See: user-manual-msd-system-5977-concept-guide-G7077-90036-en-agilent.pdf

    As with Helium, you still need 5psi or more inlet pressure at all times for good injection port pressure/flow control.  

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