Automated method for concurrent determination of thorium (Th-230, Th-232) and uranium (U-234, U-235, U-238) isotopes in water matrices with ICP-MS/MS

High-efficiency analysis of Th and U isotopes are important technical issues encountered in the fields such as environment monitoring and nuclear emergency responses. Here, we have proposed a novel automated method for the concurrent determination of Th (Th-230, Th-232) and U (U-234, U-235, U-238) isotopes in small volumes (20 mL) of water matrices. A simple chemical separation procedure was achieved with an automatic system by employing UTEVA resin as separation material, and the final eluent was compatible with direct ICP-MS/MS measurement without any extra sample preparation. Recoveries of both Th and U exceeded 90% while repeatedly running the automated separation method 70 times; meanwhile, the background levels between sample intervals remained stable and minimized. The limits of detection (LOD) for all the target nuclides of the analytical method were less than pg mL(-1); and the LODs of the minor isotopes Th-230 (0.02 fg mL(-1)) and U-234 (0.11 fg mL(-1)) were among the lowest ever reported, which was attributed to the effectiveness of the cleaning program of the automatic system and the non-interference determination of ICP-MS/MS. The merits of the analytical method were the ease of operation, good repeatability, low memory effect, and the high efficient recovery of both Th and U simultaneously. These features were advantageous for the large-scaled actual application of this method. The developed method was validated with several seawater and river water standard reference materials, where all the measured results of Th and U isotopes corresponded very well with the reference values. Finally, this method was further employed to determine Th and U isotopes in various types of real water samples and showed good practicability.