DETERMINATION OF TIN IN HUMAN BLOOD-SERUM BY RADIOCHEMICAL NEUTRON-ACTIVATION ANALYSIS

A method was developed for the determination of tin in human serum by radiochemical neutron activation analysis, using the long-lived radioisotope Sn-113 (T1/2 = 115.09 days). This radioisotope decays to a daughter isotope (113m)In, the most suitable nuclide for counting (T1/2 = 1.658 h, gamma-ray of 391.7 keV). Experience showed that, with the exception of the serum samples with the lowest tin levels, in the experimental conditions of the present study tin could mostly also be determined by using its radioisotope (117m)Sn (T1/2 = 13.61 days, gamma-ray of 158.5 keV). Samples were collected and prepared by using the procedure elaborated by the authors, which proved its effectiveness in preventing significant sample contamination on several occasions. Because samples had to be irradiated at 10(14) n.cm-2.s-1, dry ashing was necessary. After irradiation, tin was separated by solvent extraction of tin(IV) iodide from a sulfuric acid-ammonium iodide solution with toluene. The dry ashing and solvent extraction steps were exhaustively tested by means of radioactive tracer experiments whereas the accuracy and precision of the analytical method were thoroughly checked by analyzing biological reference materials (Bowen's kale powder, the NBS' bovine liver, the NBS' nonfat milk powder, and the "second-generation" biological reference material-freeze-dried human serum-for trace element determinations, developed by the authors). For tin in normal human serum, the following values were obtained: 0.502 +/- 0.096 ng.mL-1 (mean +/- standard deviation) and 0.400-0.636 ng.mL-1 (range). These values are orders of magnitude lower than those reported earlier by other investigators.