EPITHERMAL INSTRUMENTAL NEUTRON-ACTIVATION ANALYSIS OF BIOLOGICAL REFERENCE MATERIALS FOR IODINE

Epithermal instrumental neutron activation analysis (EINAA) methods ha ve been optimized and applied to several biological reference material s and selected food items for the determination of iodine. The method involves irradiation of the samples for different periods in epi-cadmi um and/or epi-boron flux of the Dalhousie University SLOWPOKE-2 reacto r and direct counting without any pre-treatment on a 25-cm(3) hyperpur e Ge detector. The 443 keV photopeak of I-128 is used for assaying the iodine content. Precision of measurements, expressed as the relative standard deviation, is 10-15% at 200-500 ppb and 3-12% at 500-6000 ppb levels of iodine. Accuracy of iodine measurements is within 5%. The d etection limits for iodine in several biological materials with cadmiu m and boron, either alone or a combination of the two, as thermal neut ron shields have been found to vary between 0.1 and 0.4 mg . kg(-1) fo r different periods of irradiation, decay and counting. The results su ggest that the EINAA methods can be successfully applied to biological materials for routine analysis of iodine at levels higher than 200 pp b.