Stable Isotope Geochemistry


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John Hill <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Fri, 19 Dec 2008 11:10:05 +0000
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Hi John

We had this fault on our Delta V only last week and changing the 
filament cured the problem.

John Hill
University College London

John Drake wrote:
> Hello all,
> I have a delta-V advantage with extremely variable box and trap 
> currents. The trap varies from 0.6 to 1.2 mA over extremely short 
> timescales (less than 0.5 seconds)- box and trap go up and down in 
> synchrony. The cycle seems to be stable for days (i.e. the currents 
> aren't changing in response to a new gas being added to the source). 
> Sensitivity and linearity are within spec, vacuum and backgrounds look 
> good, peak shapes and slow magnet scans look good, and data from a run 
> of standards look good.  Standard deviations (n= 5) for working 
> standards are  less than 0.1 per mil for d13C (Costech EA -> Conflo IV 
> -> IRMS).
> In short, the machine seems to be performing well, even with 
> hyper-variable box and trap currents. We recently had a He leak and the 
> IRMS saw room air from the Conflo for a few hours, which could have 
> damaged the filament. Thermo suggested to replace the filament, but I'm 
> hesitant to do this when we're getting good performance.
> Has anyone else seen this? Thanks,
> John Drake
> Graduate Student
> Program of Ecology, Evolution, and Conservation
> University of Illinois
> 1500 IGB
> 1206 W. Gregory Drive
> Urbana, IL 61801
> Lab phone: 217-333-1632