Dear David, There is also a chapter on isotope dilution, including an introduction and equations for calculation in my book Volume-I, which is just published. The reference is: Berglund, M. (2004) Introduction to isotope dilution mass spectrometry (IDMS). In: Handbook of stable isotope analytical techniques. De Groot, P.A. (ed.). Volume-I. Elsevier: 820-834. Hope this may be helpful, if you did not found a solution to your problem already. Best wishes, Pier. **************************************************************** Delta Isotopes Consultancy Dr. Pier A. de Groot Pastoor Moorkensstraat 16 2400 Mol - Achterbos Belgium Tel. +32 (0)14 326 205 e-mail: [log in to unmask] Visit my WEB-site about my ³Handbook of Stable Isotope Analytical Techniques², including pdf files of an order form and a flyer for downloading, at: http://users.pandora.be/handbook/index.html last update: October 1, 2004 Volume I is now available. Volume II is expected to be available medio 2005. **************************************************************** > Dear List, > > I ran across a formula on the internet, > ( http://wwwrcamnl.wr.usgs.gov/isoig/isopubs/itchch2.html ) sec 2.5.4, that I > am having trouble understanding. The equation is suppose to calculate the > final isotopic compostion when you mix two solutions of known concentration > and isotopic concentration together. There is a term F which is equal to > R/(1+R), R being the ratio of isotopes of interest. I'm not sure how F is > related to delta or at%. > I've calculated the final isotopic concentration to my own satisfaction but it > bothers me that I can't get the same answer using this equation. Thanks for > any insight into this problem. > > David DenHaan > NSTL >