Dear Alison,


      We are currently using the Sigman - Casciotti denitrifier method to
run nitrate samples.  As Cecily mentioned, we briefly used the "pyrolysis"
method for nitrates.  We have an EA capable of 1300 degrees and the system
is basically workable.  The problems that we've had were contaminant oxygen
in one run  and occasional random outliers.   The frequency of outliers
increases and precision decreased after about 30 or 40 samples. The
contaminant problem was apparent from the ratio of N2 and CO peak areas as
compared to reagent silver nitrate and this likely would not have been
suspected using the closed tube method for nitrate oxygen.  We ran our
samples and standards in duplicate in short runs as an initial work around
to the outlier problem but I'm fairly sure that improvements can be made.
There has been some discussion of causes and possible solutions for this
problem using lower temperature machines.  I've heard from people using the
higher temperature EAs (1400 degrees) who seem completely satisfied with
their systems.  Best of luck.


Steve

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]






                      Alison Bateman
                      <[log in to unmask]        To:       [log in to unmask]
                      .UK>                     cc:
                      Sent by: Stable          Subject:  Re: pyrolysis of silver nitrate for 15N and 18O ratios measurements
                      Isotope
                      Geochemistry
                      <[log in to unmask]
                      UVM.EDU>


                      05/30/2003 07:17
                      AM
                      Please respond to
                      Stable Isotope
                      Geochemistry






Dear Cecily,

We are looking to develop a pyrolysis system so that
we can measure the d18O composition of AgNO3 after
extraction of nitrate from solutions using an anion resin.

Since we are in the early stages, we would be interested
to hear your thoughts about the 'problems' that you
encountered when you tried to run samples by pyrolysis.

Many thanks,
Alison Bateman.

++++++++++++++++++++++++++++++++++++++++++++++++++++
Alison Bateman
School of Environmental Sciences
University of East Anglia
Norwich
NR4 7HU
UK

[log in to unmask]

++++++++++++++++++++++++++++++++++++++++++++++++++++



On Wed, 28 May 2003 13:26:22 -0700, Cecily C Chang <[log in to unmask]>
wrote:

>Dear All,
>
>      A comment about using the column method for pyrolyis. We typically
do
>not run samples by pyrolysis. On the few occassions that we have run
>pyrolysis samples, there were problems.
>
>      If you follow the instructions there should be no problem. Chang et
>al. 2002. CJFAS also describes using a cation column to minimize the
>organic load.  If you overload the column, if the silver is not clean,
>there will be a problem. You must check the silver nitrate for background
>nitrate. It takes us many weeks to clean silver.
>
>
>
>Cecily
>
>
>
>Cecily C.Y.Chang
>Hydrologist/Ecologist
>Stable Isotope Tracers Project
>345 Middlefield Road
>USGS Mailstop 434
>Menlo Park, CA 94025
>650-329 4471  Fax 5590
>[log in to unmask]
>
>"They that can give up essential liberty to obtain a little temporary
>safety deserve neither liberty nor safety."
>
>                                                     ----Benjamin Franklin
>
>
>
>
>                      Teppei Fukada
>                      <[log in to unmask]        To:
[log in to unmask]
>                      UK>                      cc:
>                      Sent by: Stable          Subject:  Re: [ISOGEOCHEM]
pyrolysis of silver nitrate for 15N and 18O ratios
>                      Isotope                   measurements
>                      Geochemistry
>                      <[log in to unmask]
>                      UVM.EDU>
>
>
>                      05/21/2003 01:13
>                      AM
>                      Please respond to
>                      Stable Isotope
>                      Geochemistry
>
>
>
>
>
>
>
>Hello,
>
>I am sorry for my irresponsible last e-mail.
>What I referred as "microbial method" in last e-mail is "denitrifier
>method, and
>the references are
>
>Cascioti, K.L., Sigman, D.M., Galanter Hasting, M., Böhlke, J.K. and
>Hilkert, A. 2002. Measurement of the oxygen isotopic composition of
nitrate
>in seawater and freshwater using the denitrifier method. Anal. Chem. 74,
>4905-4912.
>
>Sigman, D.M., Casciotti, K.L., Andreani, M., Barford, M., Galanter, M. and
>Böhlke, J.K. 2001. A bacterial method for the nitrogen isotopic analysis
of
>nitrate in seawater and freshwater. Anal. Chem. 73, 4145-4153.
>
>
>Thanks,
>
>
>
>Teppei
>
>
> ----- Original Message -----
> From: Rodrigo Maia
> To: [log in to unmask]
> Sent: Tuesday, May 20, 2003 10:24 PM
> Subject: Re: [ISOGEOCHEM] pyrolysis of silver nitrate for 15N and 18O
> ratios measurements
>
> Teppei
>
> How about giving a reference for the benefit of all on that "microbial
> method"???
>
> Rodrigo
>
> Rodrigo Maia
> Lab Tech
> Stable Isotopes Lab - ICAT Lisbon
> Portugal
> [log in to unmask]
> -------Original Message-------
>
> From: Stable Isotope Geochemistry
> Date: terça-feira, 20 de Maio de 2003 19:24:33
> To: [log in to unmask]
> Subject: Re: [ISOGEOCHEM] pyrolysis of silver nitrate for 15N and 18O
> ratios measurements
>
> Hello,
>
> How about measuring the gas product by gas chromatograph?
> How do you eliminate organic matters in the samples?
> Have you checked the Cecily Chang's method? Have you washed
> Ag2O before using it?
> How about eliminating anions using BaCl2 before the anion
> exchange NO3 absorption?
>
> How about the new microbial method?
>
>
> Regards,
>
>
> Teppei
> ----- Original Message -----
> From: Eddy Minet
> To: [log in to unmask]
> Sent: Tuesday, May 20, 2003 6:24 PM
> Subject: [ISOGEOCHEM] pyrolysis of silver nitrate for 15N and 18O ratios
> measurements
>
>
>
> Hi,
>
>
> Here are some of my recent problems, and I hope you may bring me some
> answers.
>
>
> I work on the measurement of 15N and 18O ratios in silver nitrate.
> Nitrates originate from groundwater and have been extracted using the
> technique issued in Silva S.R.., Journal of hydrology, 228 (2000), 22-36
> (i.e. using anion exchange resin with final neutralization by silver
> oxide). The isotopic ratios are measured by pyrolysis, with the furnace
> temperature around 1100 degrees for 15N analysis (Roboprep CN) and 1450
> degrees for 18O (ThermoFinnigan TC/EA).
>
>
> The reproducibility on both 15N and 18O has been a bit disappointing so
> far.
>
>
> In relation to 18O analyses, the CO peak looks always okay whilst the N2
> peak (that appears for m/z 28 just before the CO peak) can have a very
> strange shape, or just trails and even sometimes overlaps the CO peak.
> Whenever this first peak (N2) looks funny, and even if it doesn't seem to
> overlap the CO peak, the resulting 18O ratios hits the roof and can rise
> up to +75 per mil when other replicates would show up around +6 per mil.
>
>
> As for 15N analyses, the reproducibility is much better (standard
> deviation usually within 0.5 per mil), but results are far from what is
> usually achieved when analyzing some organic samples. Addition of some
> sucrose seems to improve a bit, but still?
>
>
> At the end, we are wondering whether the problem is just a matter of
> sample homogeneity (my silver nitrate samples look a bit like fibers or
> wool). I'll try very soon to grind finely some samples after freezing
them
> with liquid nitrogen to see if there is any improvement. Nevertheless I
> would appreciate to know if anyone of you has already experienced these
> problems and managed to work them out.
>
>
> All the best,
>
>
> Eddy Minet, Ph.D. student
>
>
> Centre for the Environment
>
>
> Trinity College
>
>
> Dublin 2 (Ireland)
>
>
> Tel: +353 (0)86 827 4921
>
>
> Email: [log in to unmask]