Complexation of Curium(III) and Europium(III) with Urea and in Human Urine

The complexation of europium(III) and curium(III) in aqueous urea solution has been studied at pH 1 – 8, I = 0.1 (NaClO4), room temperature and trace metal concentrations using time-resolved laser-induced fluorescence spectroscopy. In case of curium(III) a red shift of the luminescence maximum occurs upon complexation, while for europium(III) emission wavelengths remain unaltered but the peak splitting is changed significantly. Both heavy metals form very weak complexes of the formulae ML3+ which are stable until pH 6. Stability constants were determined to be -0.12 ± 0.05 for europium(III) and -0.31 ± 0.13 for curium(III). In human urine samples the luminescence spectra of both heavy metals differ significantly from those in water and aqueous urea solution. Red shift of the luminescence maximum of curium(III) is more pronounced and peak splitting in case of europium(III) enhanced. Besides that, lifetimes of the species formed in human urine vary markedly from those of the ML3+ complexes with urea. Furthermore, the speciation of the heavy metals seems to depend on the pH of the urine sample.