ICP-MS & alpha spectrometry for in vitro bioassay of uranium and other actinides

The Enusa Bioassay Laboratory will carry out the analyzes of the samples required by the Juzbado Internal Personal Dosimetry Service, which will be in charge of assigning doses based on all the available information and the results reported by the laboratory. Analytical techniques (high-resolution ICP-MS spectrometry and alpha spectrometry) must be sensitive enough to achieve concentrations or activities in the appropriate ranges depending on the matrix (type of sample of biological origin to be analyzed).

The isotopic determination of uranium by high-resolution ICP-MS is of great interest, not only for samples of human origin, but also for the analysis of environmental samples (water, soil, biota, atmospheric capture filters) and its application in monitoring and control of environmental radioactivity. ICP-MS spectrometry allows quantification of values ​​in ppt-ppq concentrations of the different mass isotopes. Prior to the verification and validation of the method, a series of tests were carried out in which interference was detected and confirmed in the urine matrix and in the mass of the ²³⁵U isotope. This interference makes it impossible to analyze ²³⁵U in the study and control concentrations, since adequate accuracy and precision are not obtained. This article presents the tests and verifications carried out, the instrumentation used, the first conclusions about interference, as well as future challenges and lines of work.

Currently, the internal dose assignment is carried out taking the results of the activity of the uranium isotopes, with ²³⁴U analyzed by alpha spectrometry being the one that contributes the most to it given its specific activity. The information provided by ICP-MS-HR will be of great help to know the isotopic ratios of ²³⁵U characteristic of each enrichment (since in ICP-MS its sensitivity is greater) and will provide part of the essential information to evaluate the different scenarios at the time of dose assignment, facilitating the arduous task of the internal personal dosimetry service.

Alpha spectrometry, after radiochemistry of the sample, allows the activity of the different isotopes to be analyzed, with the particularity of being able to detect ²³⁴U with great sensitivity.

On the other hand, it is intended to improve response times: ICP-MS spectrometry reports results in a short period of time and alpha spectrometry uses high efficiency resins with vacuum elutions, so analyzes of different actinides can be carried out in the same sample and reduce analysis and counting times due to the high chemical performance provided by these columns. In this way, the laboratory will be able to perform routine analyzes on workers in the sector and, in addition, have methods with short response times to be able to report results in case of emergency.