First question: did the source look ³dirty² when you changed the filament?
I usually try to rationalize what I see (my sources all look clean) since
I have no talent in cleaning sources. But I have learned that a dirty
source can cause the issues you report below. Perhaps you have a photo.
On 9/19/18, 2:44 PM, "Stable Isotope Geochemistry on behalf of Mitchell
Skuce" <[log in to unmask] on behalf of [log in to unmask]>
>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