Stable Isotope Geochemistry


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John Hill <[log in to unmask]>
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Stable Isotope Geochemistry <[log in to unmask]>
Tue, 9 Mar 2010 13:02:36 +0000
text/plain (42 lines)
Hi David

Is the filament you put in the Delta a new one or a refurbished one?
We have had problems with refurbished filaments being out of alignment 
so have switched to another source.
The box/trap ratio will change if the filament starts to sag over a 
period of time. I can't remember if the filament current on the Delta is 
box or trap regulated. If the filament partially misaligns then the box 
current certainly increase. Have you tried installing another filament?


John Hill
Mass Spectrometry Facility
University College London
Chemistry Dept.

David Psomiadis wrote:
> Dear colleagues, 
> We have a Delta V Plus connected to a GBII. Six months ago we exchanged our
> filament during regular instrument check-up intralaboratory service. After
> autofocusing the source, we applied the regular tests (diagnostic) and
> everything seemed ok. However, we noticed that the ratio box/trap changed
> from 0.7/0.8 before the filament exchange, to 0.8/0.66 . During the last six
> months, this ratio reached tha value 0.9/0.64, which is the actual ratio as
> we speak. we proceeded to cleaning of the source (clear the dark shades on
> the metal parts and on the aperture according to Thermo manual) and
> autofocus again. As this ratio should be less than 1 according to the
> manufacturers, we would be grateful if there were some ideas of how we can
> lower this ratio to reach the initial value (~0.7/0.8). The stability of the
> measurements is good, however if someone should be critical on the long
> term, he could say that there is a trend for slight instability. Any help
> will be appreciated,
> Best regards to all,
> David