The use of inductively coupled plasma mass spectrometry for the evaluation of the mobility of iodine in bentonite

Abstract

Inductively coupled plasma mass spectrometry (ICP-MS) was used for investigating iodine in deep geological repository barriers. Major problems that can arise in the method application include different behaviours of individual iodine species, memory effects and strong non-spectral interferences owing to high salt content in samples. When proper conditions were applied (i.e. the addition of tetramethylammonium hydroxide, use of Ge as an internal standard, and spiking of iodate calibration solutions with sample matrix), ICP-MS provided accurate results, irrespective of the iodine speciation. The quantification limit of iodine determination in highly saline samples was 1.1 μg/L I. The calibration was linear at least within the range of 1–100 μg/L I. The analysis accuracy was verified by an analysis of a model sample of synthetic bentonite water and a 0.1 mol/L NaCl matrix that contained various iodine species (iodide, elemental iodine and iodate) and their mixtures, and recovery ranged from 97 to 101%. The analysis by ICP-MS coupled with liquid chromatography (LC) could also distinguish between the main iodine species of iodide and iodate. The detection limits were less than 2.0 μg/L I for both species. Both ICP-MS determination of the total iodine and the LC-ICP-MS speciation analysis were applied to a preliminary investigation of iodine diffusion through Czech bentonite from the Rokle deposit. No iodide speciation changes were observed during the diffusion experiment which was performed under atmospheric conditions.