Hi Steve,
I've seen a similar thing happen when we burn 15-25mg of wood core material.
It's pretty spectacular, as it seems to puff up, then explode as the
material burns. We have similar parameters as you do, and we're getting
good numbers. I'm not sure what it is, but I'm interested to hear what the
group thinks!
Cheers,
Bob
***********
Robert Michener
IRMS Laboratory Manager
Boston University Stable Isotope Laboratory
Department of Biology
5 Cummington St.
Boston, MA 02215
Voice: 617-353-6980
Fax: 617-353-6340
Email: [log in to unmask]
Website: www.bu.edu/sil/
"You are what you eat, plus a few permil!"
***********
-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf
Of Stephen Taylor
Sent: Wednesday, April 11, 2007 11:29 AM
To: [log in to unmask]
Subject: [ISOGEOCHEM] EA - 15N : question for the list
Hi all,
We've recently been analyzing 15N in bitumen samples (it is Alberta
after all ... ) and I have 2 questions for the list:
1) does anyone have an oil standard for which a d15N value is
established? Are there any d15N values for NBS 22 out there? FYI: Our
samples are low in [N], ~0.2 to 0.4%, and to get a decent peak we are
weighing ~7 - 10 mg of material.
We've noticed a strange phenomena at combustion. (FYI : we are using
large tin cups, 20ml O2 loop, a relatively fast helium carrier flow
(~120 ml/min) and to deal with the CO2 & H2O we have inline a Nafion
drier, a large ascarite trap, Conflo dilution and a lengthy acquisition
time.
2) So ... the Flash is beautiful, but is followed by a dark "cloud"
followed in ~10 sec by another "softer" flash ... more like a intense
glow, before returning to the usual orange/red glow. The N peaks are
symmetric, ~ 700 to 1000 mV, exhibit only a minimal amount of tailing
(the 29/28 ratio returns to baseline before the diluter kicks in), so
I'm assuming the burn is sufficient? Solid standards interspersed
between the bitumen samples show no memory effect.
I'm just curious about the "two stage" burn. Has anyone else seen
this phenomena when burning material with large C:N?
Cheers,
Steve
Stephen Taylor
Lab Manager, Isotope Science Lab,
University of Calgary, Physics & Astronomy,
2500 University Dr. N.W.
Calgary, Alberta,
Canada, T2N 1N4
(p) 403 220 8268
(f) 403 220 7773
[log in to unmask]
www.phas.ucalgary.ca/isl
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