Hi Steve,

I have looked for several months for a nitrogen isotope standard for
kerogen, but I have not found any.  Please keep me in the loop if you find
one.  My analyses on NBS 22 showed very little nitrogen content, and I am
not brave enough to measure large amounts of it...  I would probably get a
C/N in the hundreds and a d15N of unknown reproducibility.  I am also
working on black shales with extremely little nitrogen content (C/N >
400), but TOC up to 17% in some samples.  The nitrogen isotopic
composition of extracted organics from these rocks (analyses with 5-10 mg)
is not trivial to interpret and could be contaminated by CO during
combustion.  This may be related to the double flash you are seeing in
your analyses.

Cheers,
Dominic





> 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
>


-------------------------------------------------
Dominic Papineau  Ph.D.
Geophysical Laboratory
Carnegie Institution of Washington
5251 Broad Branch rd NW
Washington DC 20015

Office: 202-478-8908
Cell: 303-514-8978
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