Hi Laura, depending on the compounds the fertilzer consits of you should dissolve the fertilizer in bi-dest or DI water as much as you need for following steps. Nitrates are readily soluble, sulfates in general too, phosphates are sometimes slightly soluble. Therefore, we dissolve the fertilizer with bi-dest and do the steps: 1. Nitrate-15N (Kjeldahl distillation) reducing nitrate (solution has to be NH4 free!) to NH3 with Devarda alloy in pH > 12 trapping NH3 in 0.1 N H2SO4 (N-free) drying of ammonium sulfate for 15N analysis 2. Nitrate-18O use the method described by Revesz et al: Anal. Chem 69: 4375-80; Silva et al: J. Hydrol 228 (2000) 22-36 From silver nitrate both 15N and 18O analyses are possible. 3. Sulfate precipitating SO4 with BaCl2 or Ba(OH)2 and heat it in HCl solution pH>3.5 washing chloride free, drying of BaSO4 isotope analysis on line or off line (see a lot of references); we use on-line techniques EA-IRMS (34S-SO2) and HTP-CFIRMS (18O-CO) Good luck! Gerhard *************************************** Am/Um 14:59 25.07.00 +0200 schrieben Sie: >>>> Dear everybody: I would like to know if there is a standard procedure to analyse commercial fertilisers. We would like to do some isotop analyses (d15N-NO3, d18O-NO3, d34S-SO4 and d18O-SO4) as well as a general chemical analysis. The solute part of the fertilisers is the most important one (at least for us), but how to dissolve our fertilisers? Only with DI (during how much time?), diggesting them with acid (which one could be the best one?). Is there any preventive mesure that I have to know? I will be glad to receive some answers that will help me with my work... Thanks to everybody! Laura Vitòria i Codina Grup Consolidat de Mineralogia Aplicada i Medi Ambient Dept. Mineralogia, Cristal·lografia i Dipòsits Minerals Facultat de Geologia Universitat de Barcelona Martí i Franquès s/n 08028 Barcelona Tel. 93 402 13 45 Fax. 93 402 13 40 e-mail: <[log in to unmask] <<<<<<<< ************************************************************* Dr. Gerhard Strauch Centre for Environmental Research Leipzig-Halle Ltd Department of Hydrogeology Theodor-Lieser-Strasse 4 D-06120 Halle Germany Tel: ++49/345/5585 206 Fax: ++49/345/5585 559 e-mail: [log in to unmask] ************************************************************