Varian 4000 MS - problem with filament

[Hania]

Hello everybody,

I have a 12-year old Varian 4000 MS, I've been working on it for 10 years.
As far, the filament has been burning out usually after a year. Last year we had to change the filament after 10 months, but we thought that it was due to a lot of analysis that we had been doing. However, a new filament, which has been installed on 9 February, worked for only two weeks! Yesterday I was given a communicate that filament 1 was open....
Hence my question to more experienced colleagues: what could be the cause of the crash? I use solvent delay, the samples are not concentrated, I usually switch the filament for only a short time. Any of other working parameters didn't changed. Emission current = 10 uA. Vacuum is ok. I analyse mainly food samples, in particular acrylamide and MCPD, after derivatization.
Is it possible that it is a problem with e.g. failed current sensor and filament gives too large current? Or something is not connected properly and that's why the system displays the communicate that the filament is open? Or the new filament has got some hidden defect?

[Rndirk]

Hi,

There are a couple of reasons why a filament would have such a short lifetime.

Did you take it out already, or does your source supports 2 filaments and you don't have to replace it yet? I wonder how it looks like, you can recognize a damaged filament. This narrows down the possibilities.

What's also possible is that it has literally burned up in the presence of oxygen. As your vacuum is OK, I wouldn't expect it but your vacuum doesn't tell the amount of oxygen present.

[Hania]

Thanks for answer.

I switched to the second filament because I have to finish analysing my samples. I think I wait when the second filament will be "open" then I will turn off the MS and see the filament.

[Rndirk]

That's what i also would do.

Whatever damaged the first filament, probably also damaged the second one, but less. There's a good chance it won't last long, too...

[tkubowicz]

Hello

It can be useful to switch from one filament to the other periodically (every two/three months) so that both filaments will have about the same number of hours of use. When one of the filaments fails, the second filament will fail soon after. The MSD can then be shut down once to replace both filaments.

Regards

Tomasz Kubowicz