Nuevos sistemas de microextracción dispersiva combinados con espectrometría de absorción atómica para la especiación de trazas de metales

Abstract

In this memory it is shown that ferrite, the cheapest and easiest magnetic material to obtain, can be used without the need for functionalisation for the adsorption of inorganic species in solution. The magnetic properties of these nanoparticles facilitate the separation of the solid with the use of a magnet. Desorption of the retained species in a low volume of a suitable solution achieves their pre-concentration as a pre-determination step by Electrothermal Atomic Absorption Atomisation Atomic Spectrometry (ETAAS). This is proven by the analytical procedures developed for the determination at very low concentrations of ionic silver and gold species, even achieving the discrimination (speciation) of the soluble ionic forms and the uncharged nanoparticles of these metals that can coexist in the solution. Using the same material (unfunctionalised ferrite), new and very sensitive procedures have been developed for the determination of indium and gallium, elements that have received very little attention so far with solid-phase microextraction methodologies. It is shown that if a mixture of graphene oxide and ferrite is prepared, a hybrid material is obtained that combines the advantages of both types of nanoparticles. The adsorptive properties of graphene oxide are reinforced by those of ferrite, the presence of which enables magnetic separation of the solid. Using this magnetic solid-phase dispersive microextraction methodology, followed by final measurement by ETAAS, new and very sensitive analytical procedures have been developed for the speciation of chromium (III, VI), thallium (I, III) and mercury (II and organic). On the other hand, it has also been demonstrated that separations with graphene oxide as adsorbent can be combined with the formation of coacervates in cloud point processes, which also facilitates the collection of these nanoparticles that are difficult to separate by conventional centrifugation. The selectivity of ferrite as an adsorbent material in solid-phase dispersive microextraction processes can be modified by functionalisation with simple reagents. Thus, by coating it with silver nanoparticles formed in situ and then functionalised with sodium 2-mercaptoethane sulphonate (MESNa), a new process has been developed that achieves the speciation of antimony (III) and (V) at very low concentrations. The ferrite can be used in conjunction with magnetic ionic liquids to enhance the adsorption capacity. In this way, a procedure has been developed that allows the determination of lead (II) and tin (IV) by their extraction in a magnetic ionic liquid that adsorbs on ferrite, facilitating a better separation by magnetic means. The ferrite can also be combined with an ordinary, non-magnetic ionic liquid. In this respect, a new procedure has been developed for the complete separation of silver(I) and silver(0) by means of a non-magnetic ionic liquid formed in situ and then collected with ferrite. The procedure is not only of analytical interest but also of environmental interest due to the increasing presence of these species in water and the need for their treatment. In this thesis, a total of 17 different procedures are developed for the determination and speciation, if necessary, of elements of interest in various samples such as water and soil. The procedures are reliable, as they have been verified through the use of reference materials and, when this has not been possible due to the lack of appropriate standards on the market, they have been verified through standard addition procedures and/or the use of alternative techniques to ETAAS, which is the common denominator of the work here summarised.