Francis,

Please see the following excellent review that includes insightful comments
on measuring the isotope composition of ammonium and nitrate.

Robinson, D. (2001) d15N as an integrator of the nitrogen cycle, Trend Ecol
Evolut, 16, 153-162.

Also keep in mind that the isotope ratio of inorganic N changes much as CO2
does in a canopy, except the change is over days rather than hours.  The
change in inorganic N can be up as great as 10 to 15 over a week.

Dave


***************************

R. Dave Evans
School of Biological Sciences
PO Box 644236
Washington State University
Pullman, WA   99164-4236

Office: 509-335-7466
Isotope Lab:    509-335-6154
FAX:    509-335-3184
http://www.sci.wsu.edu/sbs/faculty.php3?pageID=6&id=86&groupID=1
 
Laboratory for Biotechnology and Bioanalysis Stable Isotope Core
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-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf
Of Francis Brearley
Sent: Saturday, May 20, 2006 8:20 AM
To: [log in to unmask]
Subject: [ISOGEOCHEM] 15N of ammonium and nitrate

Dear All,

I will be working in Jamaica this summer to look at 15N in plant-soil
systems.  I will be measuring 15N of bulk soil which will be straightforward
but I am also hoping to measure 15N of ammonium and nitrate (which are the
forms of nitrogen that will be immediately available to plants and are
therefore of more interest).  Does anyone know of a method which can be used
to measure 15N of these two compounds.  

The main drawback I have is that I'll be in Jamaica while our IRMS is in
Dublin.  This means that I need to be able to process and/or store the
samples for a few weeks before being able to analyse them.  Also, I won't
really have access to a lab so the easier and simpler the method the better.

Many thanks

Francis