Jude,
Assuming you do not accurately know the concentration and isotopic
composition of carbonate in your samples (if it varies between
samples), you may not be able to apply a three component isotope mass
balance to solve for your two unknowns.
Have you considered simply removing the carbonate prior to (re-)
analysis by EA-MS? If there is remaining sample, they can be acid-
treated in silver capsules. There is a lot of discussion of this
topic on ISOGEOCHEM under carbonate removal. One most useful
methodological reference is:
Verardo, D.J, P.N. Froelich, and A. McIntyre, 1990, Determination of
organic carbon and nitrogen in marine sediments using the Carlo Erba
NA-1500 Analyzer, Deep Sea Research, Vol. 37, No.1, 157-165.
Best,
Jonathan Wynn
Department of Geology
University of South Florida
4202 E Fowler Ave, SCA 528
Tampa, FL 33620
(813) 974-9369
[log in to unmask]
http:shell.cas.usf.edu/~jwynn
On Jul 26, 2006, at 6:57 PM, judemaul wrote:
> Folks,
>
> I am characterizing particulate plant derived organic matter input
> to the soil. The approach I have taken is planting C3 plants into
> a soil with a long C4 history. The particulate organic matter in
> the soil at the start of the experiment had a del vPDB signature of
> -14.000 and the new C3 input has a del vPDB of -28.000. My problem
> is that the protocol for isolating the organic matter requires that
> I co-collect the organic matter with the sand fraction of the soil,
> which contains about 18% carbonate with a del vPDB of 0. I'm
> wondering if anybody can help me with a three source mixing model
> that can be run using only one isotope? Using a separate analysis
> of the soil I can calculate the amount of carbonate in each sample
> but I need to determine the proportion of each plant source (C3 or
> C4) in the remaining organic carbon.
> Ideally I would have removed the carbonate prior to isotopic
> analysis but at the time of sample prep I didn't realize how much
> of an issue the carbonate would be.
>
> Thanks
> jude
>
> --
> ####################
> Jude Maul
> Department of Horticulture
> Cornell University
> [log in to unmask]
> (607)255-0883 (office)
> ####################
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