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Hi Janet,

      If you intend to collect nitrate samples for both 15N and 18O by the
anion exchange column method, an improved technique for analysis uses high
temperature decomposition generally referred to either as pyrolysis or
TC-EA.  It has been shown that the newer method avoids  exchange of oxygen
with the glass combustion tube (Revesz and Bohlke, 2002, Analytical
Chemistry, V 74).   Alternatively, you may use the new denitrifier method
of Sigman and Casciotti which has several advantages (Sigman et al, 2001,
Anal. Chem 73.; Casciotti et al, 2002, Anal. Chem , 74),.  Samples are
easier to collect as no column is necessary, concentrations can be much
lower, and organics and salt are much less an issue.  If you're interested
in this method, you might contact Karen Casciotti at Woods Hole to inquire
about the possibility of getting some analyses done.  Best regards.


            Steve Silva

Steven Silva
U.S. Geological Survey
345 Middlefield Rd., Mailstop 434
Menlo Park, CA 94025
ph:  (650) 329-4558
fax: (650) 329-5590
email: [log in to unmask]





                      Janet Gabites
                      <[log in to unmask]        To:       [log in to unmask]
                      .CA>                     cc:
                      Sent by: Stable          Subject:  request for analyses
                      Isotope
                      Geochemistry
                      <[log in to unmask]
                      UVM.EDU>


                      06/14/2005 04:32
                      PM
                      Please respond to
                      Stable Isotope
                      Geochemistry






I received the following request for analyses. We are not set up for this,
so I offered to post to the list in the hope that some other lab can help.

Thanks,
Janet Gabites


>We are doing a research in a highland lake here in Colombia trying to
>discriminate sources of NO3 pollutants. We need to know the levels of 18O
>and 15N in water samples of stream and lake waters. Current NO3 levels
range
>from 3 to 25 mg/L. We want to trace nitrate sources using natural stable
>isotopes (15N and 18O). We expect to use the method describe by Silva et
al,
>(2000) (A new method for collection of nitrate from fresh water and the
>analysis of nitrogen and oxygen isotope ratios S.R. Silva a, * , C.
Kendall
>a , D.H. Wilkison b , A.C. Ziegler c , C.C.Y. Chang a , R.J. Avanzino a).
>
>I would like also to know if your laboratory has the capability and
>availability to process and analyze around 300 samples using the resins
>describe by Silva. If positive I would  appreciate you can give me an idea
>of the costs for processing this material and the procedures to follow in
>case we use your services.
>
>Sincerely,
>
>
>Jorge Rubiano
>Postdoctoral Research Fellow
>Land Use Project
>CIAT- International Center for Tropical Agriculture
>Cali
>Colombia
>
>[log in to unmask]
>Tel: 572-445-0493  or 1-650-833-6625
>Fax: 572-445-0073 or 1-650-833-6626
>http://gisweb.ciat.cgiar.org
>http://www.waterforfood.org

Janet Gabites,
Stable Isotope Facility,
Pacific Centre for Isotope and Geochemical Research,
Department of Earth and Ocean Sciences,
The University of British Columbia,
Vancouver, B.C. V6T 1Z4
ph 604-822-6654
fax 604-822-6088
http://www.eos.ubc.ca/research/pcigr/PCIGR.htm