Dear Seth, I have conducted a series of experiments to see what effect oven drying at 60°C and freeze-drying has on a variety of ammonium- and nitrate-containing solutions either in low or higher concentrations (standards dissolved in bidest water) regarding the effects on recovery and nitrogen isotopic composition ... I will have a look for the exact results and mail them to your personal email address - or if there is some handwaving, to the isogeochem list - tomorrow. Have a nice day, Christian. -- ------------------------------------------------------------------------ Christian Ostertag-Henning tel: ++49-9131-852-2660 (office) Institute of Geology ++49-9131-852-6243 (lab) University of Erlangen-Nürnberg fax: ++49-9131-852-9294 Schlossgarten 5 D - 91054 Erlangen email: [log in to unmask] ------------------------------------------------------------------------