Development, validation and verification of an ICP-MS procedure for a multi-element analysis of uranium ore concentrates
The International Atomic Energy Agency (IAEA) uses information from characterization of uranium-bearing material samples to support the verification of states' declarations and to look for indications of possible undeclared materials and activities. Parameters of interest include, among others, the concentrations of elemental impurities, the patterns of rare earth elements (REE), and the isotope ratios of uranium and some impurity elements. These data along with other physical and chemical properties are being used to assess material quality, monitor chemical processes, and verify material origin. This manuscript describes a Sector Field-Inductively Coupled Plasma-Mass Spectrometry (SF-ICP-MS) procedure for the determination of 67 minor and trace elements, including REE, in uranium ore concentrates (UOC) and related compounds without matrix separation. All elements are measured within one instrumental sequence, which improves the timeliness of the analyses. A particular focus is set on developing a reliable quality control mechanism in the absence of uranium-bearing reference materials with certified concentrations of all analysed elements. In order to provide objective experimental evidence that the particular requirements for each specific parameter are fulfilled the validation process included (i) assessment of measurement uncertainties, (ii) analysis of available certified reference materials with uranium matrix (validated for 31 elements), and (iii) measuring test samples in the frame of four inter-laboratory comparison exercises (validated for 54 elements). The majority of the analysed elements could be measured with a satisfactory accuracy but determination of difficult-to-analyse elements, such as silicon and tungsten, requires a modified sample preparation and measurement procedure. An alternative ‘non-destructive’ analytical method, such as XRF or laser ablation ICP-MS, can be applied for direct analysis of non-dissolved residues that remain in the digests.