We have an unsolved problem ongoing concerning our MS system. Your help would be much appreciated. 

GC : 7980A

MS : 5975C

Description : Since our last ionisation chamber cleaning, some Autotune values has change drastically. Since then, the sensibility decreased a lot and we are no longer able to observe compounds under around 1000ppm which is definitely not normal

Values before cleaning, when the signal was OK : EMV 1812 / Gain Factor 0.56 / Ent Lens 25.50 / Ion Focus 90.2 / Repeller 28.28 / Ent Lens Offset 19.075

Values after cleaning, bad signal : EMV 2388 / Gain Factor 50 / Ent Lens 35 / Ion Focus 39.9 / Repeller 34.81 / Ent Lens Offset 13.302

I checked the ionisation chamber installation 3 times, everything is ok. After a long discussion with an Agilent MS specialist, I decided to buy new Repeller, Repeller insulators, Lens insulator, Ion focus lens, Entrance Lens and Extraction Cyclinder. All the metals parts had a lot of micro scratches on them which may disturb the current according to him. 

Unfortunately, after installation of the ionisation chamber with the new pieces, the Autotune values and the signal didn't change...

If someone has a suggestion about what to do, that would be much appreciated. 

Thank you !

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  • Compare the parameters from November side-by-side with the ones from January. They are very different. The first thing that I look at is the HiVac - why is the vacuum so much better than before?  It says Column Flow is 1, but something changed to allow the vacuum to go lower.  The tune will be different with different flow into the ion source.

    All the lenses are different, and not just a little bit.  I would guess from these two tunes that the source connections are wrong - the Ion Focus and Entrance Lens wires are reversed.  Blue to the Back....is the way I remember it.    

  • Thanks for your answer  .

    We changed the location of our vaccuum pump and electric plug of our vaccuum pump recently. The pumps were just below the GC-MS. They are now  on the floor below. I am not sure it is the reason why the void changed though. However, we had void similar to the the one in the old ok Autotune at the begining of January (2.10-5) and the Autotune was also bad so i don't think our problem is void-related.

    I just checked and the blue (Entranse Lens) and orange wires (Ion Focus) are unfortunately not reversed...

    Anyone has any other guess ?

    Thank you.

  • Troubleshooting poor tunes starts with carrier gas flow, column installation, having enough PFTBA, then vacuum, and after that it is nearly always contamination related, either the lenses, the insulators, the filaments, or some combination.  A dirty system can contaminate replacement parts or a freshly cleaned source quite quickly as the adhered organic layer inside redistributes all the time.  Next it could be electronic connections, like the ceramic source connector board wires that connect to the lenses - but those can be tested with a volt/ohmmeter when the system is vented and opened up.

    The tuning parameters are very different. At some point the best thing to do is to contact your country's local Agilent service toll-free phone number.

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