Determination of depleted uranium in fish: Validation of a confirmatory method by dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS)

Depleted uranium (DU) is a by-product of the uranium enrichment process for nuclear fuel. According to the Commission Decision 2002/657/EC, a confirmatory method for the quantification of DU in freeze-dried fish was developed by isotope ratio dynamic reaction cell inductively coupled plasma-mass spectrometry (IR-DRC-ICP-MS). A preliminary study was performed to determine the following parameters: instrumental detection limit (IDL), isotopic ratio measurement limit (IRML), percentage of DU (PDU) in presence of natural uranium (NU) and limit of quantification (LoQDU). The analyses were carried out by means of IR-DRC-ICP-MS. Ammonia was the reaction gas used for the dynamic reaction cell. In addition, a sector field inductively coupled plasma mass spectrometer (SF-ICP-MS) was employed to calculate the within-laboratory reproducibility. For the confirmatory method the following parameters were determined: (a) trueness; (b) precision; (c) critical concentrations alpha and beta (CCα, CCβ); (d) specificity; (e) stability. Trueness was assessed by using the recovery tests. The recovery and within-laboratory reproducibility were determined by fortifying the blank digested solution of dogfish tissue: six aliquots were fortified at 1, 1.5 and 2 times the LOQDU with 25.0, 37.5 and 50.0 ng L−1 or 4.16, 6.24, 8.32 μg kg−1 with a recovery of −8.2, +9.5 and +9.6%, respectively and a within-laboratory reproducibility (three analytical run) of 15.5, 8.0 and 11.0%, respectively. The results for the decision limit and the detection capability were: CCα = 11.69 ng L−1 and CCβ = 19.8 ng L−1. The digested solutions resulted to be stable during testing time (60 days) and the method can be considered highly specific as well.