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Dear Handrew,
high mass 30 and relatively low 29 and 28 is probably due to an excess of
nitrogen and oxygen in the source, that is  30 = 14N16O.
Have you also checked the background on 18 and 32?
If  you have checked the leaks and these masses are still high, you coud try
with a longer back-out (300 C for 12-24 hours) with the heaters-on on your
mass spectrometer and a higher He-flow (100 ml/min and/or higher than 1 bar
on manometer).
Regards.

Tiziano Boschetti.

----- Original Message ----- 
From: "Andrew Campbell" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, December 13, 2007 10:54 PM
Subject: [ISOGEOCHEM] TC/EA thermocouple


> I noticed a question on Isogechem a few years back requesting an
> north American supplier for the TC/EA thermocouple MAT number
> 1121470.  I'm referring to the thermocouple on the main furnace at hi
> temperature.  Mine burned out two weeks ago and my spare burned out
> yesterday.  Finnigan says they are back ordered for 6 weeks.
>
> Has anyone discovered another place to buy them??
>
> I am also curious about the life span of the GC column in the
> TC/EA.  I was having problems with background when running CO.  I was
> able to bring down the background on 28 and 29 by backing out at 300
> C but mass 30 stayed fairly high.  My TC/EA is 4 year old.  Is there
> any reason to change the GC column.  I also understand that the
> Chrompack column is no longer available.  has anyone tried a substitute?
>
> Dr. Andrew Campbell
> Professor of Geology
> Earth and Environmental Sciences
> New Mexico Tech
> Socorro NM 87801
> 575-835-5327
> Please note new area code
>
>
> -- 
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