129I analysis of seawater at KIST: Carrier and carrier-free extraction techniques, an inter-laboratory comparison of results, and an alternative to ICP-MS 127I concentration measurements

Abstract

Studies for 129I analysis by accelerator mass spectrometry (AMS) are presented. Alpha Aesar KI product 10978 (99.995 % purity) was measured to have 129I/127I = 1.6x10-14, suitable for use as carrier and background material. Iodine extraction from seawater using chloroform and n-hexane with iodine carrier showed hexane to have advantages and > 80 % extraction yield. An “iodine carrier-free” extraction method, co-precipitating other halides native to the seawater as carriers, was found to have > 98 % extraction yield. Results of seawater 129I concentrations measured at 3 AMS laboratories averaged 10 % agreement, similar to the last comparison 20 years ago. Conversely, 127I concentrations measured by ICP-MS were in good agreement between only two laboratories. Seawater 127I concentrations calculated from AMS results for samples treated using both carrier and carrier-free methods were in agreement with ICP-MS measurements, suggesting an alternative for 127I concentration measurements. Data for 8 Korean coastal seawater samples are also presented.