There is a student here at Stanford that is trying to measure 15N in
NO3-K2SO4 and 15N in NH4-K2SO4. These samples have be enriched by
approximately 50 o/oo. 50 to 70ul of sample are loaded into liquid capsules
in a helium atm using a micro pipette and sealed. The liquid capsule was
pre-weighed prior to sample introduction and re-weighed after sealing to
determine the amt of solution in the capsule. These samples were then
loaded in a carousel on a NA1500 EA attached to a Delta+ via continuous
flow. The EA is setup to run C and N (i.e., reactor column with chromium
oxide and silvered cobaltous, the reduction column with copper wire, mag
perchlorate for water trap and a 4 m GC column).  Standards run before,
during, and after these solutions have precision better than 0.1 o/oo for
N. The solutions, however, are variable (as much as 5 o/oo).

Great lengths have gone to insure the accuracy of the spike solution and
mixtures, reduce/prevent evaporation, reduce/prevent exposure to atm N. It
is possible we have not gone far enough in preventing the introduction of N
from outside sources. In the past we have had success analyzing liquids for
13C, but this is the first time we have looked at 15N in liquids. For
various reasons we would like to be able to analyze the liquid and not use
a media (e.g., chomosorb) to absorb the liquid. However, we are open to
these methods too. Using a technique such as diffusion packets (i.e.,
Devarda's alloy , etc) is an option but the sample sizes are small and we
feel there would be too much error associated with using this technique as
a result of sample size.

If there is anyone out there that routinely analyzes liquids for 15N with
success we would appreciate your comments either to the list or directly.

Thanks,

Dave



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David A. Mucciarone
Laboratory Manager
Stanford University
Department of Geological and Environmental Sciences, 320
Stanford, CA 94305-2115
650-723-0817 (office) 650-725-2199 (fax)
Office - Green Earth Sciences Rm. 331
Stanford Stable Isotope Laboratory - Green Earth Sciences Rm. 332 & 334.
e-mail: [log in to unmask]
WWW: http://pangea.stanford.edu/isotope/dam
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