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Stable Isotope Geochemistry

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Subject:
From:
Howard Sanford <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Date:
Mon, 23 Feb 2004 09:18:51 -0500
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At 04:29 PM 2/22/2004, you wrote:

>I have a hopefully quick question about running enriched d15N
>samples.  I've done this before and know about the possibilities of
>contaminating the various columns in the EA.  However, before the
>samples were only somewhat enriched (100 permil).  When testing a
>recent batch of samples to see just how enriched they where one
>sample gave a value of 4000!  I've already told the researcher that
>he must weigh his samples elsewhere.  I don't want this stuff loose
>in the lab.  Now my question.  Is there any danger to the mass
>spectrometer (i.e., the collectors) if we run such obscenely enriched
>samples?

I run both natural abundance and enriched 15N on my Delta Plus system. I
routinely run 10% 15N (~29,000 permil) and have not had any problems with
contamination of the mass spec. Fortunatly I have 2 EA's and 2 Conflos, one
for enriched only and one for natural abundance, so it makes it fairly easy
to switch back and forth and not worry about what's happening in the EA
columns. Though even the enriched EA settles back down to normal (or close
to normal) after several natural abundance samples.

I actually looked into this problem several months ago when I had someone
that wanted to run 80% 15N, which for me seemed obscenely high, so I
understand your apprehension. After talking with several other labs that do
continious flow enriched work I decided it could be done without risk to
the mass spec, but carry over in the EA from sample to sample would just be
too large to make it practical to do. Eventually I diluted the samples with
natural abundance material to get it down into the 25-30% range, which
worked OK, but still had a fair amount of EA carryover.

Howard

Howard Sanford
919-513-3039
North Carolina State University
Dept. of Soil Science
Box 7619
3114 Williams Hall
Raleigh, NC 27695
http://www.soil.ncsu.edu/services/sims/

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