New methods for the speciation analysis of radioactive iodine in aqueous samples

Abstract

Radioactive iodine in the environment comes both from nature and as a result of human activities. Understanding its behavior and fate in the environment, to enable assessment be made of its environmental impact, requires knowledge of its chemical form (speciation). The aim of this research work was to develop new analytical methods for the identification and measurement of radioactive iodine species, with an emphasis on the measurement of iodate and iodide in aqueous bsamples. A new derivatisation-solid phase extraction (DSPE) method was developed based on the conversion of iodine species to 4-iodo-N, N-dimethylaniline (IDMA) which was then extracted from the aqueous sample by using solid phase extraction. Stable iodine could be measured by HPLC determination of IDMA, giving a detection limit of ~1?mol L-1 for both iodide and iodate when a sample size of 250 mL was employed. DSPE methods could also be adapted to collect individual 129I species as radioactive IDMA, with final measurement by liquid scintillation counting (LSC). The mean recoveries from determining 129I- (~9.2 Bq g-1) and 129IO3 - (~0.52 Bq g-1) in water were 96.5±2.6 % and 94.6±0.8 %, respectively. These adapted methods were applied to the speciation analysis of 129I in an effluent from a nuclear facility without pre-separation. The inorganic forms of 129I in the effluent were iodide, iodate and elemental iodine. To overcome salt-derived interferences during DSPE analysis of seawater, an anion exchange approach was developed to pre-separate and enrich iodide and iodate from seawater (1 litre) prior to re-enrichment using the DSPE method. Total yields of iodide and iodate obtained from this combined approach were 81.6±1.8% and 79.1±7.7%, respectively. The concentration-based detection limit could be improved by using ICP-MS detection. Whilst the combined methods could enrich the concentrations of inorganic iodine species in seawater by 200-fold, some incomplete separation of iodide from iodate was however observed. Both methods were shown to offer simple and selective approaches to the speciation analysis of both stable and radioactive iodine in a variety of sample types

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