Hi Geoff

You might try to check full scan or m/z 32 & 40, when needle valve is opened and closed. And check the vacuum is normal or not under both modes. It will help you to isolate where the main problem comes from.

If machine works good, you may check the He supply to the IRMS system is ok or not. I mean that maybe you checked the He pressure is ~ 1 bar on conflo but actually He is not supplying well. I meet similar situation before, and the problem is that there is not enough He going to the MS. It might comes from needle valve leaking, capillary(one or both) blocked/moved/broken.

Cheers,
NJ

Dr. Nai-Jung, Wan 萬乃容
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-----Original Message-----
From: Stable Isotope Geochemistry <[log in to unmask]> On Behalf Of Geoff Schwaner
Sent: Tuesday, April 5, 2022 12:22 AM
To: [log in to unmask]
Subject: [EXTERNAL] [ISOGEOCHEM] Delta V Advantage Reference Dilution Issues

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Hello IsoGeoChem,

I am running a Delta V Advantage - EA Isolink CN - ConFlow IV setup, and have had an interesting issue come up. In the middle of a set of on/offs while in CO2 mode, the signal suddenly maxed out for all 3 cups. This was not a software bug or freeze up, the detector was simply maxed out. I turned off the Ref II main valve, and the issue still persisted. I had to turn off the CO2 valve as well before the signal started to very slowly decrease. I then checked the N2 configuration, which had similar issues. Mass 28 was maxed out, along with mass 30, and mass 29 was much higher than usual as well. Turning the N2 reference gas valves on or off does not seem to have any effect on the N2 signals, they stay that way regardless. Box and trap values seem normal, and it is a fairly new filament.

Troubleshooting I have already tried to resolve this:
Restarting the Delta V
Reseating the amplifier cards
Deleting and recreating dynexternal files Restoring to a previous working version handler file

When all of that failed to change anything, I started playing around with the tuning, and was able to get the signal intensities down by changing trap voltage, electron energy and extraction, but it is still not behaving correctly. One key thing I noticed: I tried re-determining reference gas dilutions, and the max dilution is ~1%.  I tried running a few standards at increasing sample dilutions to see if sample dilution is still working, but the signal backgrounds are too messed up to detect peaks.

Could this be a He flow controller issue? Has anyone run into this issue before or think of any additional troubleshooting I can try?

Thank you,
Geoff Schwaner
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