Development of emerging analytical techniques for speciation studies
- Autores: Pepita Pla Vilanova
- Directores de la Tesis: Josep Galcerán Nogues (dir. tes.), Encarnacio Companys Ferran (codir. tes.)
- Lectura: En la Universitat de Lleida ( España ) en 2020
- Idioma: español
- Tribunal Calificador de la Tesis: Jaume Puy Llorens (presid.), Enriqueta Anticó Daró (secret.), Liping Wang (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería y Tecnologías de la Información por la Universidad de Lleida
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
This thesis offers new insights for the speciation techniques field, based on the measurement of free ions concentrations. Two main contributions are: (i) the detection of novel different elements for the discipline and (ii) the improvement of the techniques.
The first part focuses on the electrochemical determination of two trivalent elements such as In and Sb. Lately, both elements have received attention, because of their increasing applications and possible effects on the environment. So, appropriate and reliable analytical techniques, for both elements, are necessary. For the analysis of In, we measured total and free In concentrations in a solution using two complementary electroanalytical techniques, SCP (Stripping chronopotentiometry) and AGNES (Absence of gradients and Nernstian equilibrium stripping), both implemented with the TMF/RDE (Thin mercury film/rotating disk electrode). We achieved nanomolar limits of detection for both techniques. Also, AGNES was employed to study the dissolution of In2O3 nanoparticles, given its wide technological use. pH and the effect of the labile ligands in solution affected significantly free In quantification. We also studied the advantages of using the TMF/RDE in front of the HMDE (Hanging mercury drop electrode), achieving shorter experimental times even when determining extremely low free In concentrations. Sb measurements represent the first application of AGNES to detect one particular specie of Sb(III) in an aqueous solution. Since Sb as a free ion is practically non-existent, because of the extensive hydrolysis of the element, the detection methodology was based on following Sb(OH)3(aq) concentrations. Two different AGNES variants were studied for Sb analysis and were compared. The variant AGNES-Q yielded acceptable results but needed very long stripping times. On the other hand, a clear advantage was presented by AGNES-SCP, which demonstrated to be faster and more reproducible. This promising methodology opens the way to tackle Sb speciation with AGNES in other systems and media.
The second part of this thesis focuses on improving DMT's (Donnan membrane technique) applicability and efficiency. It was performed studying a variety of modifications, based on the following sets of concepts: experimental variables, instrumental modifications, and acceptor composition. The first set improved the efficiency and robustness of the technique, ruling out any potential effect from the sample (donor) stirring, the temperature of the system, and the sampling of the acceptor. Conversely, the instrumental modification is based on optimizing the surface-to-volume ratio, modifying the dimensions of the field cell as well as employing hollow fibres. Such modifications represented to be an effective and simple way to shorten the experimental time. The last set of experiments is based on the tuning of acceptor's composition and it revealed new strategies to overcome significantly major drawbacks of the DMT technique. Lower supporting electrolyte concentrations in the acceptor than in the donor solution presented a significant reduction of the experimental times. On the other hand, higher supporting electrolyte concentrations in the acceptor than in the donor, allows to measure more diluted samples.
