CI Autotune/Sensitivity - Issue 5975 XL


our 5975XL is not performing according to the specifications when using Chemical Ionization. Our tune files look like the ones described in the following question: Sadly no resolution was found there.



We tried the following:

1. Swaping the gasline from A to B

2. Changing the gas supplier from Air Liquide to Linde (both methane 5.5)

3. Cleaning of the source

4. Using another source body from an older CI-Source

5. Baking out of source an quadrupole

6. Checking for leaks in EI mode. Nitrogen is about 4 %. Evaluation tune ist successful. EI ist working fine.

7. Changed the CI gasfilter.

An Agilent representative suggested filling up PFDTD. But if PFDTD might be emtpy we would not see any signal at all? For NCI sensitivity ist bad. That is especially the case for m/z above 500 (PBDE und PBB Analysis). PCI checkout as well as NCI checkout do not result in the right S/N. Both are way to low; at least 3 - 5 lower than what we should expect. Unfortunately last year our GC was upgraded with a new sampler an inlet (PTV), so we suspected that some problems may arise from this but all our measurements in EI-mode perform perfectly.

We hope that somebody has an idea on how to resolve this issue, because we need the MSD for brominated an fluorinated substances.

Thanks for any input concering this issue.

  • I forgot to mention that we changed the filament too

  • Thank you for the details.  Source cleaning and filament replacement should be first every time, of course. Making sure that there is enough PFDTD is in the vial should be done when the system is vented and the column is being replaced at least once in a while as that is the easiest time to pull the MS away from the GC and look.

    Has the entrance lens been 0.0 on both tunes historically on your system?  That is unusual.  I verify that the Blue wire connection to the source is to the Back, that's the entrance lens - and the orange wire is to the front, that's the Ion Focus.

    Column flow 1.5 is high.  The total gas flow into the ionization chamber in CI is very critical.  1.2 ml/min of helium column flow and methane reagent gas 20% for PCI, 40% for NCI is recommended.  Your PCI tune that optimized at 14 is not typical.   The NCI tune does not optimize the reagent gas flow, by default it sets it to 40%.  That might not be correct for your system.  Go into Manual Tune, repeat profile scan on the tune ions, and change the reagent gas flow.   If PCI is only 14% instead of 20%, maybe your NCI will be lower?

    Has the methane reagent gas supply pressure ever exceeded 30 to 35 psi?  The CI reagent gas flow controller is damaged at higher pressures. 

    How old is the tip seal?  The ceramic gets contaminated by sample residue and should be replaced.  The timing is the dreaded "as needed" as the contamination is already there before it can be seen.

    From the manual --- In PCI: Check the interface tip seal by looking at the m/z 28 to 27 ratio (in the methane flow adjust panel).  Determine if a gross air leak is present by monitoring the ions at m/z 19 (protonated water) and 32.

    And let us know....

  • Thanks for your fast response.

    The entrance lense used to be at 15. But some tunes in the past showed 0.0 too. If we ramp the entrance lense in PCI we see the max for both m/z 267 and m/z 599 is between 0 and about 20. 

    The wires are connected correctly.

    I changed the column flow for PCI to 1.2 mL/min and set the gas flow manually to 20. Unfortunately the tune file for PCI did not change; the intensity of the high masses is still too low compared to tunes from last year. Also i set the entrance lense manually to 15. 

    28/27 with a flow of 20 has a higher ratio than with the optimized flow of about 14 (it sometimes is a bit lower or higher). But it is still in the recommended range described in the manual.

    The seal is (very) old. It was never replaced. I can not say how many measurements were done with it. We will try another seal which we have lying around from an older 5975 or 5973, not sure. As we only changed the source body (older 5975 or 5793) but did not use the other seal. We will carefully clean the seal with some IPA and a Kim Wipe. 

    While doing this we will look for the calibrant although we still have signals for the 267 and 599 as can be seen from the ramp above. 

    In the past the gas supply was at 5 bar (about 70 psi). I turned it down to about 1.7 bar (about 25 psi) when i started working with the system, Agilent recommended this. With this pressure we achieved all the specifications. We could turn down the pressure even more. Maybe this will help?

    So maybe the controller is broken and for some reason it worked last year. Is there any possibility to check for a defective controller? At the moment we cannot afford a service from agilent.

    I forgot to mention that we already checked for leaks in PCI. m/z 19 and m/z 32 are virtually not existent. So the system should be leak free. We even added a miniscule amount of Apiezon to the O-ring because we are aware of the negative influences of air on NCI. 

    Today we will change/clean the tip seal and look for the calibrant.

  • 5 bar (70 psi) damaged the CI reagent gas flow controller, G7000-80030. That part is about $10k USD plus travel and labor.  The high pressure means that now the default NCI setting of 40 is not delivering 40%.  It might be worth trying an experiment. If PCI is optimized by the tune algorithm at 14 - is that a percentage change or an absolute change?  20 minus 6=14 or 14 is 70% of 20?   Try NCI at 40 minus 6 = 32   and try at 28.    

     IPA and a wipe will not do much to the tipseal. It is ceramic, so a bit porous, and the sample residue is in all of those pores and cooked on the surface. The attached spring makes it difficult to clean thoroughly.  The adhered organic layer is a semiconductor so in CI the repeller/ion body voltage may not be at the setpoint if there is leakage current to ground across that layer.

    As you said, you see tune ions so there is probably PFDTD in the vial, but having enough in there is smart to check.

    Leak checking in CI is only valid if the reagent gas and tuning are at least mostly valid. Yours isn't so you can't really rely on the leak checking. It might be fine, but might not, you won't know until the tuning is closer to typical.  The best way to leak check CI is to switch back to EI. 

    If you apply high vacuum grease to an O ring, wipe all of it off. That still leaves enough in the pores in the O ring and a few atoms thick residue to make the seal without causing other issues.

    and let us know what happens!

  • Thank you for your answer.

    I am just wondering why it worked last year after years of too high pressure and this year it does not work anymore. While installing the new gas bottle, i by mistake turned the valve to high about 4-5 bar, but nothing compared to the years of too high pressure. For our new instrument we will look into buying an additional pressure regulator as the one attached to the gas bottle is not fine enough. Maybe the CI was damaged while moving the instrument for the installation of the new sampler. But the biggest problem ist that the instrument was installed 14 years ago and the operators changed during that time. Since we will get a new instrument next week we will probably not spent the 10k € for the repair and the old one will remain an EI machine which it does perfectly hopefully for many more years to come.

    We found a new tip seal which was ordered years ago. It did not change the PCI tune. Still m/z 267 and 599 are too low. We did not look into NCI because the last tune was not different from the old ones. The PFDTD vial is full. So this is not the problem. CI gas regulation works since changing the values manually changes the appearance of the spectrum of PFDTD. So it is probably not completely broken and the issue might reside somewhere else in the system - at least i hope so.

    The O ring was just covered with a small amount of Apiezon and afterwards rubbed with a Kimwipe.

    Last thing we will try is switching back from gas inlet B to A. When we will notice a change in the PCI Tune we will try NCI again with a different gas flow as mentioned by you.   

  • First tune after changing to gas line A

    looks promising...

    second tune after changing to gas line A

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