GC-MS Tune 5975 - Air and Water Leak Check


What is the acceptable criteria for the Air and Water leak check on a GC-MS?

For 69, 18, and 28, I have a relative abundance of 100, 1.61, and 1.15. This seems really low. Can you please give me suggestions as to what I should do?

Thank you!

Parents Reply
  • I changed the septa, ran the tune report, and this is what I got. 

  • Here EM volt is showing 171...Am i right..

  • The air/water percentages are relative to the abundance of 69 and the 69 abundance is adjusted during the tune.  The spectral tilt, the relative abundances of 69/219/502 are also adjusted during tune and that tilt affects the air/water check, too.   So your system has very low 219/502 and that skewed spectral result could tell you that the air/water percentages are not necessarily valid.   The fact that N2 and O2 are very low compared to water is probably correct, though, as that is comparing ions that are near each other. Water takes some hours to pump out of the MS after maintenance. If it's still there after a day or so and there is no N2:O2, then the water is coming in with your carrier gas.  

    The low 219/502 needs to be resolved first. I would vent and check that the column is not extended too far out of the transferline.  Sticking too far out is bad but a little bit too short is not bad.   If it were me and I had the system vented,  I would also remove the source and take it apart to inspect it.  I may even quickly clean it so that I didn't have to vent again -- even if it was just cleaned.   Take a look at: Eliminate the Fear of Mass Spec for comprehensive source cleaning videos.

    The HiVac at 0 means that the ion gauge tube is turned off or is bad.  The HiVac reading is done by a glowing filament that has a limited lifetime and needs to be replaced when it's broken.  In Manual Tune you can try to turn it back on.  If it does not it probably needs to be replaced.

    And from your tune history report.  What happened on October 27, 2021 between 16:13 and 17:08 ?  At 16:13 the 69/219/502 was 100%, 82%, 6%... and at 17:08 it was 100,30,1.28 ...  Also, please stop tuning when the ion source is not at temperature.  It takes the ion source at least a few hours to become thermally stable and provide consistent results.

  • Thank you for your help, Paul. I'm not sure what happened on October 27. Many people use this system.

    This morning, the system passed the Tune Evaluation, but the HiVac is still off. I looked at the Manual Tune task box, but do not see where I have an option to turn it on. Can you explain more about this?

    The lights on the back of the MS are green. Do you think the ion gauge has failed?

  • Gauge on/off was in older software, sorry.  The LEDs are green -- on the gauge itself, too?

    If it passes tune eval and everything else about the system is fine and the instrument is, oh, greater than four or five years old I would bet on the gauge, yes.

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