Hi Anthony,


A misaligned filament (i.e. not dead centre but slightly below or above the 
ideal bisecting line) will not cause this kind of problem.

Trap and box current will not be that different from 'normal'; i.e. not 
that you notice. Theoretically, they should both be 0.75 (and add up to 
1.5) but I have seen 0.72 paired with 0.78 with perfectly aligned 
filaments.

Also, a slight misalignment will not cause a 90% drop in sensitivity. More 
likely than not, sensitivity will look OK (more or less, and any slight 
drop can be corrected for by tuning) but there might well be a problem with 
isotopic linearity.

The only other reason (reported on this list) for a dramatic loss in 
sensitivity (other than misaligned gas inlet holes) was contamination of 
source components.


Cheers,

Wolfram



On Mar 8 2006, Anthony L. Michaud wrote:

> Christina,
> 
> It sounds like Benny and Wolfram know what's going on. For future 
> reference for some of us (me), could you say what your filament, trap, 
> and box current are when you are getting this low signal?
> 
> I'd assume that if the filament was misaligned then the trap and box 
> current would be very different from their usual values. I don't have 
> experience with this but would like to keep it as a mental note in case I 
> am faced with this problem in the future.
> 
> Thanks.
> 
> Anthony
> 
> 
> ------------------------------------------------------
> Anthony L. Michaud
> W. M. Keck Foundation Laboratory for Environmental Biogeochemistry
> Department of Geological Sciences
> Arizona State University
> Tempe, AZ 85287-1404
>  
> Web: http://kfleb.asu.edu
> Tel: 480-727-8033
> Fax: 480-965-8102
>  
> Mailing address:
>  
> Anthony Michaud
> PSF-686
> Arizona State University
> Tempe, AZ 85287-1404
>  
> ***Windsurf Everywhere***
> ------------------------------------------------------
>  
> -----Original Message----- From: Stable Isotope Geochemistry 
> [mailto:[log in to unmask]] On Behalf Of Christina Biasi Sent: 
> Wednesday, March 08, 2006 1:22 AM To: [log in to unmask] Subject: 
> [ISOGEOCHEM] low intensity
> 
> Dear list members,
> 
> we are running a conflow Thermo Finnigan Delta plus XP. After cleaning 
> the ion source 2 weeks ago we are suffering from the following problem: 
> our intensity is very low. Mass 44, e.g., is around 100 mV, and it used 
> to be 6000mV. Since the calibration scan finds some peaks, we assume that 
> the filament is at least working. However, we took the ion source out 
> again already 2 times, and checked the filament position, the pins, all 
> connections...although we found indeed once a loose connection, now all 
> these parameters should be fine. But again there is far too low 
> intensity. When tuning the ion source the intensity changes a little bid, 
> but not very much. Can anybody help us with this problem? Any 
> recommendations are highly welcome!
> 
> Thanks!
> 
> Christina
>