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]