Dear Isogeochem users,

We run waters on a TCEA/DeltaV+ IRMS. Recently I've been trying to sort out some issues that started with a dying filament; I replaced it but couldn't seem to get normal signal intensities, no matter how much focusing I did. I then put in a different, new filament and got normal signals, but in the several days since, have been dealing with a number of other issues:
-The focus settings don't seem to be stable. I can optimize the focus, and then a day later, or even less, they seem to shift. This is very noticeable when doing a test run, the reference peak intensities will slowly decrease. Also the Extraction seems to be optimized at an unusually low point, about 20% (usually in the past it's been >80%). Electron Energy optimum is also lower than normal, around 106eV, and the X-Deflection is maxed out at 0%. Oddly enough though, the peak shape is now better than ever...
-The On/Off stability is fine, but the linearity with CO is not great... changing 0.4-0.5permil from ~2-9V. I cannot seem to improve this; normally in the past decreasing the emission, or simply letting the machine sit for a while, will help improve linearity, but that doesn't seem to be the case now
-When running repeat injections of test samples (over a range of values), the raw values for a given sample shift/drift throughout the course of the run. We'd had similar issues in the past, but it seems worse now.

If anyone has any ideas what is causing these issues, I'd be most appreciative. An Isomass tech suggested cleaning the source, which I will likely attempt, but I am skeptical that that is the problem since these issues (for the mostpart) just cropped after the filament changes (and I don't see how that could have significantly affected the source cleanliness).


Mitchell Skuce