An application of the total measurement uncertainty budget concept to the thermodynamic data of uranyl (VI) complexation by sulfate

On the basis of UV–Vis absorption spectra from 33 aqueous solutions with a multivariate composition in uranium (VI), sulfate, and hydroxide, the evaluation of a complete measurement uncertainty budget of relevant physicochemical quantities describing the system is performed. The analysis was performed by threshold bootstrap computer-assisted target factor analysis and revealed the presence of the species UO2SO4and(UO2)2(OH)22+. The analytical procedure is scrutinized to identify and quantify relevant influence factors on the basis of cause-and-effect analysis. The complete measurement uncertainty budgets are obtained as empirical cumulative distribution functions, which show a marked non-Normality. Evidence is given that the apparent discrepant results reported in the literature, especially for formation constants of species (UO2)2(OH)22+, are not a result of faulty experimentation but of neglect of relevant uncertainty contributions. Thus, reliability has been considerably overestimated – making the results of different independent studies incompatible.