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
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www.phas.ucalgary.ca/isl