PB McIntyre,

The problem with the low concentrations of NH4 and preservatives is that
although the microorganisms
may be killed their enzymes may not be. I suspect, but cannot prove that
was a past problem with some
work we attempted years ago.

Glen Martin




                    "Peter B.
                    McIntyre"             To:     [log in to unmask]
                    <[log in to unmask]       cc:
                    DU>                   Subject:     preserving water samples for
                    Sent by: Stable        NH4-N isotopes
                    Isotope
                    Geochemistry
                    <ISOGEOCHEM@LIS
                    T.UVM.EDU>


                    06/05/02 07:41
                    AM
                    Please respond
                    to Stable
                    Isotope
                    Geochemistry






I am looking for advice on the best method for preserving water samples
(125 mL and 1 L volumes per sample) for NH4-N isotope analysis.  My field
work is at several relatively-remote tropical freshwater sites, and it will
be easier for me to bring water home than to conduct diffusions at the
field sites.  Ambient concentrations of NH4-N are low at both sites (2-10
ppb, or say 0.5 uM), which is why I need relatively large volumes of water
for each sample. Rather than use ion exchange resins, I would like to
preserve the samples for transport back to the USA.

If any one has experience working with mercuric chloride, chloroform,
H2SO4, or HCl as preservatives for this purpose, I would really appreciate
your suggestions as to which is best.  I am reluctant to bring such
toxic/caustic substances on the plane with me (especially the strong
acids), so advice on that subject would be useful too.

Thanks for your help!

Pete McIntyre
PhD candidate
Ecology and Evolutionary Biology
Cornell University



----------------------------------------------------

Peter B. McIntyre
Dept. of Ecology and Evolutionary Biology
Corson Hall, Cornell University
Ithaca, NY 14853-2701
U.S.A.