Development of a single method for direct measurement of multiple radionuclides using ICP-MS/MS

Abstract

Tandem inductively coupled plasma mass spectrometry (ICP-MS/MS) has demonstrated effective online removal of interferences for a number of medium and long-lived radionuclides including ⁹⁰Sr, ¹²⁹I, ^135/137Cs and ²³⁷Np. This reduces or removes the dependence on relatively time consuming offline chemical separation, improving sample throughput and offering economic benefits for end users through reduced procedural time, analyst time, secondary waste arisings and quantity of resins and reagents required. This work demonstrates the development and application of a method for measuring multiple radionuclides (including ⁶³Ni, ⁹⁰Sr, ⁹³Zr, ⁹⁹Tc, ¹²⁹I, ²³⁷Np, ²³⁹Pu) and stable elements in various sample matrices in a single measurement. Separate instrument modes customised for individual radionuclides were combined into a single run, each using a different instrument setup depending on the extent of interference removal required. The measurement time was approximately seven minutes and consumed 3.5 mL for each sample. Instrument conditions were optimised for each radionuclide using stable and radioactive standards, and then validated using samples including aqueous wastes from a nuclear site, air filters following microwave dissolution, groundwater, and soil, sediment and concrete samples following borate fusion dissolution. Matrix-matched calibration standards were prepared, and a multi-element standard solution was used as an internal standard. The limits of detection were compared to regulatory limits, which showed that longer-lived radionuclides such as ⁹³Zr, ⁹⁹Tc, ¹²⁹I and ²³⁷Np can be directly measured, whilst shorter-lived radionuclides such as ⁹⁰Sr and ⁶³Ni require separation and pre-concentration prior to sample introduction. The method provides a significant amount of information on stable and radioactive composition in a single measurement, with the potential to further expand the number of radionuclides measurable as part of this single procedure.