Study of metal-ligand species by ESI-MS: The case of La, Nd and Th complexes with EDTA

Electrospray ionization-mass spectrometry (ESI-MS) has been used to investigate the speciation of La, Nd and Th in the presence of the complexing agent EDTA. Two methods of sample introduction were optimized and compared: direct infusion and flow injection, without chromatographic column. The species found were independent of the sample introduction method applied. The dependence of the species response with ESI parameters and focusing of ions was studied, and a significant change in relative intensities was observed while no differences in the species found were detected. The predominant species were always the same. System behavior was evaluated by varying the pH and the metal/ligand ratio. The results are consistent with literature data. Although the linear range is rather small (10− 4-10− 5 M), this technique could be useful to identify the species in equilibrium in different chemical environments. System behavior for mixtures of metals and for a mineral water sample was studied. The characterization of formed complexes will contribute to understand their environmental mobility.