Threshold bootstrap target factor analysis study of neodymium with pyridine 2,4 dicarboxylic acid N-oxide—an investigation of traceability

Threshold bootstrap computer-assisted target factor analysis (TB CAT) has been applied to the evaluation of UV-Vis spectra of Nd(III) in aqueous solutions containing varying amounts of pyridine 2,4-dicarboxylic acid N-oxide (dipyr NO). Using the total uncertainty budget concept, probability distributions of the conditional formation constant(s) of the respective Nd(III) dipyr NO species have been evaluated. The experimental data are compatible with two different systems: a single Nd(III) dipyr NO species with log     β 11 = 2.8 ± 0.11 or, alternatively, a two species system with log     β 11 = 3.7 ± 0.35 and log     β 12 = 5.2 ± 0.8 . The results seem to favor the single species interpretation. However, a discussion of the influence of spectral correlation indicates that the situation should be considered with caution. The results are compared to a previous TB CAT study on Nd(III) picolinic acid N-oxide interaction illustrating the advantage of arguing in terms of probability density functions. The pyridine N-oxides with substituted carboxylic acids are structurally poorly investigated. Hence, this study calls for more structural information on rare earth pyridine N-oxide derivates.