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- Posts: 10
- Joined: Tue Oct 19, 2021 1:28 pm
- Location: Ottawa, Ontario, Canada
4 days ago I vented my Agilent 5975C MSD to clean the source and trim the GC column. Did the usual maintenance, changed the liner, reinstalled the column. I have alot of experience doing this and usually things go well.
I pumped down the instrument over the weekend and came in this morning to just tighten the inlet and MSD auxiliary nuts and noticed that everything seemed good, the turbo pump was at 100%, MSD status was "OK".
But, when I did the tune, in CI mode (NCI), I got the message "cannot achieve constant peak widths". I tried to tune a few more times, same problem. I checked the PFDTD level, and it was 1/8-1/4 full, so that's not the problem. I know that I connected all the wires correctly to the MSD source. The filament seems to be working because I can see thru the clear source's window that it lights up when attempting to tune. I also ran a Methane pre-tune in PCI mode to check for leaks and there is no peak at 32 m/z, the ratio of m/z 17 to 19 is 17 is much, much higher than 19, so showing that there is no air or water in the source.
On thing that concerns me is that in the diagnostics display it shows EMV = 0. Shouldn't it be 1100-1200? Is my filament broken? If so, why does it glow when tuning?
Any more troubleshooting ideas anyone might have? I would like to avoid venting the MSD, but it looks like I'm going to have to do it....sigh.
Update: a few hours later....I decided to vent the MSD and install the EI source. I pumped it down successfully then waited an hour over lunch for the vacuum to stabilize. I think ran an air/water leak check and got: 2.93% water, 0.38% O2, 1.84% CO2 and 55.43% N2/water. I think this does not indicate a serious leak? If it were a leak, I should be getting very high CO2/O2 values n'est ce pas?
Update2: I decided to check the CI source body and look more closely for any shorts that might be existing. Got out the ol' multimeter (MM), set it to continuity mode and started probing. Nothing. I even checked to see if the filament was continuous, yes indeedy it was. So, filament is ok, the source body is ok...what else could it be? I decided to run the EI tune again and see if there were any improvements over the last 25 mins, and I ran a Tune evaluation as well. The abundances were higher, and the H2O percent was down to 0.96%, so looks like the vacuum pump was doing it's job. But still, why the strange "cannot achieve constant peak widths" error when I tuned the MSD in CI mode this morning? I guess I'll just replace the CI filament and hope for the best, reinstall the CI source and pump it down overnight. I'll find out tomorrow morning how it went and I'll let you all know. I know you're all excited to find out what happened so I'll try to post the results early.
Update3: Sad news...tuned the CI MSD and same error as before: "cannot achieve constant peak widths". I thought I saw one fraction of a second where it started to form nice tuning peaks, but probably it was just wishful thinking and my mind was just manifesting what IT wanted to see. So I'm back to where I started....alone, out of ideas, with a broken MSD in NCI mode. *sigh*
Update4: So, I tried tuning it in PCI mode...that's positive chemical ionization for you folks out there that aren't familiar with chemical ionization. I actually successfully tuned, albeit not very easily, but it tuned. I then did a methane flow setup tune and that went fine. One weird thing was that the MSD had to ramp the methane flow from 20 to 40 to get the correct ion ratios for the PCI tune. Not sure why. I checked the methane gas tank and it was delivering 28 psi and still had 250 psi left in the tank. So that means the methane was still available. I then tried to tune in NCI mode again....but got that same error: "cannot achieve constant peak widths". I switched back to PCI, tuned again in PCI and now IT could not tune and gave the same error as NCI. At this point I'm running out of ideas. If anyone can help please do. My next troubleshooting step is to plug the MSD with a no-hole ferrule and try tuning it separated from the GC. Personally, I think this step is a waste of time...but it's worth a shot. What do I have to lose, right?