New Method Enables Accurate Measurement of Iodine-129 in Decommissioning Wastes Using ICP-MS/MS

A team of researchers from the National Oceanography Centre at the University of Southampton and the National Physical Laboratory in Teddington has developed an optimized method for the precise measurement of iodine-129 (¹²⁹I) in decommissioning wastes using tandem inductively coupled plasma mass spectrometry (ICP-MS/MS). The study, published in the Journal of Analytical Atomic Spectrometry, highlights the advantages of this approach for sensitive and efficient analysis of ¹²⁹I, providing a cost-effective alternative to other measurement techniques (1).

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Accurate measurement of ¹²⁹I, a long-lived fission product, is crucial for waste characterization and long-term monitoring of waste facilities and the surrounding environment. The researchers aimed to explore the capabilities of tandem ICP-MS/MS for the rapid and routine measurement of ¹²⁹I in nuclear wastes. This method is particularly well-suited for high-throughput analysis and offers improved sensitivity compared to other mass spectrometric and decay counting techniques.

The study focused on addressing the multiple interferences encountered during accurate ¹²⁹I measurement by ICP-MS. The tandem setup demonstrated its effectiveness in removing isobaric, polyatomic, and tailing interferences. Additionally, the researchers investigated the importance of matrix modification and the selection of an appropriate internal standard to enhance sensitivity. By optimizing these parameters, the team achieved remarkable results.

In the context of ICP-MS/MS, isobaric interferences refer to situations where ions of different elements have the same mass-to-charge ratio (m/z). These interferences can lead to inaccurate measurement of the target analyte as they can overlap with the signal of interest on the same m/z channel. Polyatomic interferences occur when ions containing multiple atoms interfere with the analyte signal, often resulting in distorted measurements. Tailing interferences, on the other hand, are caused by incomplete ionization or incomplete desolvation of sample ions, leading to skewed peaks and potentially affecting the accuracy and precision of the measurements. Effective removal of these interferences is crucial for obtaining accurate and reliable results in ICP-MS/MS analysis.

Applying the optimized setup to various decommissioning waste simulants, the researchers achieved an impressive instrument detection limit of 1.05 × 10⁻⁴ Bq/g (0.017 ng/g) for ¹²⁹I. This limit is two orders of magnitude below the target out-of-scope limit of 0.01 Bq/g (1.57 ng/g). The measurements obtained using ICP-MS/MS showed good agreement with those obtained through liquid scintillation counting (LSC), further validating the accuracy and reliability of the method.

The study demonstrates the feasibility of rapid, routine, and low-level measurement of ¹²⁹I using ICP-MS/MS for end-users in decommissioning and environmental monitoring. This optimized method offers several advantages, including improved sensitivity, cost-effectiveness, and high throughput. By accurately characterizing and monitoring ¹²⁹I in decommissioning wastes, stakeholders can ensure proper waste management and protect the environment effectively.

The development of this optimized method for ¹²⁹I measurement using ICP-MS/MS marks a significant step forward in the field of nuclear waste analysis. It provides a valuable tool for researchers and professionals involved in waste characterization, decommissioning, and environmental monitoring. The ability to achieve accurate measurements at low levels opens avenues for better waste management practices and contributes to the safe and sustainable disposal of nuclear waste.

Reference

(1) Zacharauskas, Z.; Warwick, P.; Russell, B.; Reading, D.; Croudace, I. Development of an optimised method for measurement of iodine-129 in decommissioning wastes using ICP-MS/MS. J. Anal. At. Spectrom. 2023, ASAP. DOI: 10.1039/D3JA00045A