Stable Isotope Geochemistry


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John Drake <[log in to unmask]>
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Stable Isotope Geochemistry <[log in to unmask]>
Thu, 18 Dec 2008 09:29:34 -0600
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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