A study of iodine loss during the preparation and analysis of samples using 131I tracer and neutron activation analysis

Abstract

The recoveries of various species of iodine, such as I^–, IO₃^– and organic iodine, in the procedures of acid digestion, ashing, freeze-drying, evaporation drying and neutron irradiation were studied using ¹³¹I tracer and instrumental neutron activation analysis. The recoveries of iodine were over 99% after drying at room temperature and 60–80 °C for various iodine species in all kinds of media. The organic iodine in various media, I^– and IO₃^– in biological materials and IO₃^– in alkaline solution were not lost after freeze-drying, whereas I^– in aqueous solution and IO₃^– in acidic and neutral solution were significantly lost. The recoveries of iodine were different under various acid digestion conditions. Under the optimum conditions, more than 96% of iodine remained in the digestion solution. With ashing, the recovery of iodine was less than 2%. Addition of alkali to the samples can significantly improve the iodine recovery, but the ashing is incomplete in this case. Only 90% of iodine was recovered using alkali ashing at 650 °C. Neutron irradiation did not cause any loss of iodine.