DETERMINATION OF SELENIUM AND ZINC IN HUMAN SERUM BY INSTRUMENTAL NEUTRON-ACTIVATION ANALYSIS WITH A CERIUM INTERNAL STANDARD

An instrumental neutron activation analysis (INAA) method for simultaneously determining the Se and Zn concentrations in serum specimen was developed in order to study and clarify the associations between prediagnostic serum Se and Zn, and the subsequent risk of lung and stomach cancer in which the amount of available sera was quite limited. Cerium was used as an internal standard in order to maintain the accuracy and precision, even with less than 0.2 ml of a sample and short measuring time. Samples, (0.1 is similar to 0.2 ml), and Se-Zn standard solutions were mixed with exact amounts of the Ce standard solution, respectively. After lyophilization, the samples were sealed in a high-purity quartz tube. The Se-Zn standard solutions were also scaled in a quartz tube without lyophilization. The samples and standards were irradiated in the JRR-2 with a thermal neutron flux of more than 2.2 X 10(13) n cm-2 S-1 for 265.5 hours. After cooling for one month, about 5 mum surface layers of the quartz ampule for the samples and standards were etched with hydrofluoric acid; gamma-ray spectra were then measured with a Ge(Li) detector. The contents of Se and Zn were obtained from the peak area of gamma-rays of 145, 265 and 1115 keV for Ce-141, Se-75 and Zn-65, respectively. The relative standard deviations of the analytical results among the 14 independent samples were 3.0 and 5.0% for Se and Zn, respectively. The accuracy of the present method was confirmed by the satisfactory agreement between the results obtained by the present method and those obtained by other methods, including the certified values of NIST Standard Reference Materials of Bovine Liver (SRM1577, SRM1577a).