Hello, The following paper is now available in the J. Fish. Aquat. Sci. A Method for nitrate collection for d15N and dO18 analysis from waters with low nitrate concentrations. Stop by step instructions are available from Cecily Chang. See address below. Cecily Chang -- Cecily Chang MS 434 U.S. Geological Survey 345 Middlefield Menlo Park, CA 94025 tel 650 329 4471 FAX 5590 [log in to unmask]