Rich,
I have not tried to analyze whole soil for 18O but do 18O regular in
cellulose, using a heavily modified system similar to that used by G.D.
Farquhar et al, (1997, Rapid Communications in Mass Spectrometry, Vol II,
1554-1560).
We had one batch of samples that was and absolute disaster with huge drift
in the calibration and quality control samples. We eventually traced this
to the apparent use of glass beads to grind the cellulose. Apparently,
some of the glass had powdered and mixed with the cellulose, and was
affecting the analysis. Certainly quartz tubes or even a lower purity
alumina cannot be used for this analysis as the oxygen in the quartz of
alumina interferes with the analysis.
I would expect that in a soil with aluminum and silica oxides would suffer
from the same problems. I imagine it will be necessary to extract the
organic matter from the mineral soil before analysis.
Hope this helps,
Paul Brooks.
At 07:55 AM 2/22/2007, you wrote:
>Johnkarl-
>
>Thank you for your prompt reply. The papers are helpful as will the
>contacts at NIST. I was unfortunately not specific enough about the
>source of the 18O I will be measuring. I'm not looking at the soil
>water or extracted soil nitrate, but the solid soil itself, washed of
>available nitrate, then dried and ground for analysis of the 18O in the
>solid organic component. I was hoping someone might have experience
>with the natural abundance of the solid component of the soil. Thanks
>again
>
>Rich
>
>
>--- Johnkarl F Bohlke <[log in to unmask]> wrote:
>
> > Rich-
> > For nitrate oxygen isotopes, there are several reference materials
> > with
> > different d18O values, as described in the attached paper from RCM.
> > Best
> > place to get them at present is the IAEA (AQCS) website, although
> > NIST is
> > supposed to be distributing them, too. At NIST, you could ask these
> > contacts:
> > [log in to unmask]
> > [log in to unmask]
> > These materials are not highly enriched, but they have a pretty large
> >
> > range of d18O and they should indicate if there are problems with
> > blanks,
> > fractionations, etc., if you put them through the complete analytical
> >
> > procedure. Also note that different procedures may have more or less
> > of a
> > problem with this measurement (see attached paper from AC).
> > Good luck.
> > JKB
> >
> >
> > John Karl Böhlke, Hydrologist
> > US Geological Survey
> > 431 National Center
> > 12201 Sunrise Valley Drive
> > Reston, VA 20192
> > 703-648-6325
> >
> >
> >
> >
> > Rich MacLean <[log in to unmask]>
> > Sent by: Stable Isotope Geochemistry <[log in to unmask]>
> > 02/16/2007 10:52 AM
> > Please respond to
> > Stable Isotope Geochemistry <[log in to unmask]>
> >
> >
> > To
> > [log in to unmask]
> > cc
> >
> > Subject
> > [ISOGEOCHEM] 18O in northern forest soils
> >
> >
> >
> >
> >
> >
> > I am beginning an experiment involving the addition of 18O enriched
> > nitrate to soil taken from a red pine forest in Massachusetts, I will
> > be performing the experiment and running the samples on the mass spec
> > myself. I am having difficulty finding numbers for the natural
> > abundance of 18O in the O horizon of forest soils to judge the
> > validity
> > of results returned from unlabeled soils, and was hoping that someone
> > on the list might have experience in this area and know a range of
> > values I might expect to see? I was also hoping someone might be
> > able
> > to suggest standards to run with the soil? Right now all the lab has
> > is standardized sucrose, with a delta 18O at about 36 per mil. My
> > thanks for your time and any help you can offer.
> >
> > Rich MacLean
> >
> >
> >
> >
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