check these publications:

Kaehler S, Pakhomov EA, 2001. Effects of storage and preservation on the delta C-13 and delta N-15 signatures of selected marine organisms. MARINE ECOLOGY-PROGRESS SERIES 219: 299-304

Feuchtmayr H, Grey J, 2003. Effect of preparation and preservation procedures on carbon and nitrogen stable isotope determinations from zooplankton RAPID COMMUNICATIONS IN MASS SPECTROMETRY 17 (23): 2605-2610

Ana Colašo
IMAR- Dept Oceanography and Fisheries-Univ of Azores
Cais de Sta Cruz
9901-862 Horta
Phone: +351-292200436
Fax: +351-292200411