Development of new low-level method for the analysis of iodine 129 and the isotopic ratio 129I/127I determination
Résumé
Iodine is an extremely volatile element naturally present under various organic or inorganic forms with different oxidation states (-1, 0, +1, +5 and +7). These physico-chemical characteristics complicate its extraction and quantification. Among the 37 iodine isotopes, 127I is the only stable one and 129I is the radioisotope with the longest half-life (16.1 x 106y). 129I is chronically and regulatory released by fuel reprocessing plants e.g. La Hague (France). For environmental monitoring and radioecological studies, particles, organic and inorganic gas 129I is often trapped in filter and active charcoal. To analyse 129I in environmental samples, an extraction step allows the extraction of iodine from solid matrix. Then, the purification is essential to eliminate the matrix components and interfering isotopes. This step could also allow the improvement of detection limits by a concentration of a large quantity of sample. Solvent extraction is the most used technique to isolate iodine from the matrix components. However, it is time consuming and often requires the handling of hazardous substances. Liquid
chromatography and more specifically extraction chromatography appears to be a more convenient
technique than solvent extraction. Despite the efficiency of γ-spectroscopy and LSC to quantify 129I in contaminated samples, the detection
limits provided are often higher than the environmental background. Furthermore, none of these techniques allows the determination of 129I/127I isotopic ratio. Mass spectrometry (e.g. ICP-MS* and AMS**) is an excellent alternative for the determination of 129I and
129I/127I isotopic ratio. In this work, a safe and innovative method to quantify 129I and 129I/127I in charcoal and air filters samples was developed. It is based on an acid digestion, optimized by DOE***, followed by a purification with solid phase extraction, usually meant to be used with LSC. It was adapted to ICP-MS measurement and the elution medium was meticulously studied with the aim to be compatible with ICP-MS measurement while minimizing spectral and non-spectral interferences. The isobaric interference due to 129Xe was drastically reduced by reaction gas using ICP-MS/MS.Excellent figures of merits including a signal gain > 20 and the memory effect elimination were obtained.
The achieved performances allowed decreasing the detection limit for 129I (2 mBq for solid sample) and 129I/127I (10-9) with excellent accuracy and precision. This method was successfully applied to analyse particulate and gaseous 129I sampled on air filters and charcoal near La Hague reprocessing plant
Domaines
Chimie analytiqueOrigine | Fichiers produits par l'(les) auteur(s) |
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