Iodine analysis of biological samples by neutron activation of 127-I, with scintillation counting of Cerenkov radiation.

To measure the small amounts of iodine in tissues, organelles, and subfractions it is necessary to use very sensitive and specific analytical methods. Neutron activation analysis meets these criteria; the measurement of lZ81 after irradiation of the naturally occurring isotope, 1271, has a sensitivity of about 0.08 nanogram (12). However, neutron activation analysis has the disadvantage of requiring instrumentation not generally available in biological laboratories; given the availability of a nuclear reactor, &counters or -y-spectrometers have generally been necessary to measure radioactivity and ensure specificity. We have measured nanogram quantities of iodine in small biological samples using a combination of postirradiation extractions to separate Cl and Br (1,2) with timed counting of the resultant lzsI in aqueous solution, utilizing Cerenkov radiation.