A novel time-resolved laser fluorescence spectroscopy system for research on complexation of uranium(IV)

Research on the chemical speciation of complexes by determining the fluorescence properties of metal ions whose emitted fluorescence lifetime is in the range of only few nanoseconds, has been very limited to date due to a lack of the technical possibilities necessary to conduct respective measurements. We were able to overcome the technical problems and set up a new time-resolved laser fluorescence spectroscopy system that meets the requirements to carry out research on the fluorescence properties of metal ions with very short fluorescence lifetimes such as uranium(IV) and its compounds. We investigated the fluorescence of uranium(IV) in perchloric acid and determined the detection limit of uranium(IV) to be 1 ± 10-6M. Additionally, we found the fluorescence decay time of uranium(IV) to be 2.73 ns ± 0.40 ns. Further application of the novel laser system addressed the complexation of uranium(IV) with fluoride by studying the fluorescence properties during reaction. Evaluation of the data recorded resulted in the finding of a 1 : 1 complex (uranium(IV) : fluoride). We determined the corresponding complex formation constant of uranium(IV) fluoride (UF)3+ with logβº = 9.43 ± 1.94. The application of our novel time-resolved laser fluorescence spectroscopy system demonstrated that speciation measurements of metal ions and their compounds with very short-lived fluorescence lifetimes can be conducted successfully. Using this laser system, analytical investigation of such elements and compounds is possible in environmentally relevant concentration ranges.