Dear Laura:

It's not a good idea to acidify samples for storage because you might lose some
nitrate. You can safely store the sample for one month at 4 degree C without
any preservatives but not longer than that. You may use HgCl to preserve the
sample for room temperature storage. Or you can use NaOH if you do not need the
NH4+ for analysis.

Dachun Zhang
Stable Isotope Lab
ZymaX

Laura Vitoria wrote:

> Hello everybody:
>
>  It's the first time I am writing here and then I would like to
> congratulate the existence of  this ISOGEOCHEM e-mail list.
>
>  I am a PhD student working in contamination in river and ground waters by
> commercial fertilisers and animal or sewage wastes. I am doing 15N/14N
> analyses but I have a doubt about sample storage life.
>  I read in "Environmental Isotopes in Hydrogeology" (CLARK & FRITZ,
> 1997-8?) that samples for 15N/14N (from dissolved NO3 and NH4) and for
> 18O/16O (from dissolved NO3) analyses have a storage life at 4ºC of about 3
> month, and that they must be acidified to pH 2 with HCl-
>  Is it that true?
>  Has anybody else another experience?
>  What about frozen samples?
>
>  If I could have any reponses at these questions it would be very helpfull
> for my work
>  Thanks in advance,
>
>  Laura Vitòria i Codina
> Grup Consolidat de Mineralogia Aplicada i Medi Ambient
> Dep. Cristal.lografia, Mineralogia i Dipòsits Minerals
> Facultat de Geologia
> Universitat de Barcelona
> C/ Martí i Franqués s/n
> 08028 Barcelona, Spain
> Tel. 34-93-4021345; Fax. 34-93-4021340
> e-mail: [log in to unmask]