Luminescence properties of uranium(VI) citrate and uranium(VI) oxalate species and their application in the determination of complex formation constants

For the first time, the interaction of uranium(VI) with citric acid and oxalic acid in aqueous solution was investigated using time-resolved laser-induced fluorescence spectroscopy (TRLFS) between pH 2 and 4. The complex species UO2cit- and (UO2)2(cit)22- formed in citrate medium as well as UO2ox and UO2(ox)22- formed in oxalate medium show no luminescence emissions at room temperature. However, by coupling the fluorescence measurement technique with a low temperature system (-120 C, cryo-TRLFS), emission signals of the various complex species could be detected. The emission signals are bathochromic shifted in comparison to the emission maxima of the uncomplexed uranium(VI) cation. Using the spectroscopic data, the corresponding complex formation constants were calculated, which corroborate literature data. (orig.)