Novedosas aplicaciones de las redes metal-orgánicas y otros materiales en conjunción con técnicas microextractivas para la determinación de contaminantes

  1. Priscilla Rocío Bautista
Supervised by:
  1. Ana María Afonso Perera Director
  2. Verónica Pino Estévez Director

Defence university: Universidad de La Laguna

Year of defence: 2018

Department:
  1. Química

Type: Thesis

Teseo: 566712 DIALNET

Abstract

Recent efforts in Analytical Chemistry are devoted, among others, to the use of environmental-friendly methods following the principles of Green Analytical Chemistry, in order to minimize the organic solvent consumption and sample requirements; to simplify the entire procedure; to use novel and less toxic materials; while keeping adequate sensitivity, reproducibility, and extraction efficiency. Thus, microextraction procedures appear as an interesting approach to fulfill these requirements. Microextraction methods using solid-sorbents, and thus having as a mandatory requirement the use sorbent amounts lower than 500 mg, are the focus of the current Doctoral Thesis. Among microextraction methods using solid sorbents, it is worth mentioning the miniaturized version of the solid-phase extraction (µSPE). µSPE requires two main steps, the extraction, where the analytes are retained into a solid sorbent; and the elution (requiring few microliters of a solvent) or the desorption (requiring high temperatures), to free the analytes retained in the sorbent in order to subject them to the further analytical determination. The dispersive version of µSPE (D-µSPE) is a simpler approach, which justifies its applicability worldwide. In this mode, the solid sorbent is directly added to a liquid sample solution containing analytes. Then, it is subjected to external stirring, such as: vortex, magnetic stirring or ultrasounds to favor the interaction sorbent-analyte. Once the extraction procedure is finished, both phases (solid and liquid) are separated. The second step is the elution or desorption of analytes, in a similar manner to that of µSPE. Furthermore, there is an improvement of the D-µSPE method due to the incorporation of magnetic sorbents, termed magnetic-assisted D-µSPE (M-D-µSPE). The procedure is totally identical to that of D-µSPE, but in this case the sorbent is easily separated from the liquid sample and non-wanted components by the application of an external magnetic field (a strong magnet). This method simplifies considerably the methodology, not only in terms of velocity, but also reducing sources of errors and number of stages in the extraction procedure. Solid-phase microextraction (SPME) is another quite successful microextraction strategy. It utilizes a fiber coating (7-100 µm, depending on the nature of the material) onto a 1 cm support as the key device for its analytical performance. It has a number of advantages such as robustness, high thermal and chemical stability, simplicity, fastness, and high sensitivity, while being an organic solvent-free procedure (and thus environmental-friendly) in the majority of the cases. The latter is because the majority of studies describe the combination of SPME with gas chromatography (GC), facilitating the direct desorption of analytes in the GC injector, whereas the SPME coating keeps its integrity. The incorporation of novel sorbent materials in analytical microextraction schemes is also hot topic nowadays within a Green Analytical Chemistry perspective. Several novel materials have been reported in the recent literature as promising sorbents in µSPE, such as molecular imprinted polymers, carbonaceous materials (carbon nanotubes and graphene), metallic nanoparticles, and metal-organic frameworks (MOFs). Regarding MOFs, the research included in the present Doctoral Thesis is one of the pioneering studies in the use of MOFs in D-µSPE, M-D-µSPE and SPME. MOFs merit citation among novel materials in sample preparation, due to their unique properties. MOFs are porous hybrid materials that exist as infinite crystalline lattices, composed by metal ions and organic linkers. They have accessible cages, tunnels and modifiable pores. Their nano-scale porosity is evidently accompanied by the highest surface area known (from ~200 to ~6000 m2·g-1), which undoubtedly makes them promising sorbents for analytical schemes. They also have a crystal structure, and high thermal and chemical stability. Considering their chemical and physical properties, and using rational design (at least from a theoretical point of view) it is possible to prepare an infinite number of new MOFs with diverse structures, topologies and porosities. In this sense, the main objective of this Doctoral Thesis was the development of new analytical microextraction methodologies combined with adequate chromatographic techniques, using MOFs and its derivatives as novel sorbent materials for a variety of compounds in different samples, with adequate analytical performance and compiling with Green Analytical Chemistry requirements. This Doctoral Thesis has been divided in five chapters: Chapter I is a general introduction, overviewing microextraction techniques, the incorporation of novel materials in such methods, and the potential characteristics that MOFs can confer to these procedures . Chapter II, includes the experimental section of all studies undertaken in the current Doctoral Thesis. Chapter III covers all research in the field of D-µSPE incorporating MOFs. In this chapter, Section III.1 includes a review article to give an overview of the use of MOFs in D-µSPE schemes. Section III.2 study the extraction performance of several MOFs for a group of parabens using D-µSPE, being the first article of this kind in sample preparation. Section III.3 includes the first attempt in gaining insights in the nature of the interactions that are established between MOFs and analytes in D-µSPE. This study was accomplished evaluating the extraction efficiency of different MOFs and different analytes. Section III.4 focuses on the synthesis and characterization of a novel and green MOF, and its successful use as sorbent in D-µSPE for a group of contaminants in waters. Finally, Section III.5 shows the preliminary results obtained in the evaluation of UiO-66 and its derivatives regarding the analytical performance in D-µSPE for a group of contaminants with different structures. UiO-66 derivatives include –NH2 and –NO2 as functional groups of their ligands. Thus, it is studied for first time the influence of the functional groups in the analytical performance of MOFs sharing the same crystal structure. Chapter IV is devoted to applications of MOFs in M-D-µSPE. Section IV.1 includes a book chapter on the different applications of magnetic materials, based on magnetite particles (Fe3O4), in magnetic-facilitated procedure. Section IV.2 includes the research on the preparation of a magnetic composite based on MOFs, using a simple mixing approach. The M-D-µSPE application is related the determination of polycyclic aromatic hydrocarbons in waters and tea infusions. Section IV.3 shows the preparation of a heterogeneous magnetic composite based on MOF, also tested with polycyclic aromatic hydrocarbons in M-D-µSPE. Chapter V is the last Chapter of this Doctoral Thesis. Section V.1 includes a research article on the use of MOFs in SPME. Section V.2 includes the preparation of novel SPME fibers based on MOFs, together with the preliminary results of their use to extract a variety of compounds. The analytical applications of the research studies included in Chapters III and IV have been carried out using high-performance liquid chromatography or ultra-high performance liquid chromatography, and in combination with a variety of detectors (UV-Vis, DAD, FD, or MS) depending on the group of analytes and/or the specific applications. The analytical applications of the research studies in Chapter V have been carried out using gas-chromatography with FD or MS detection. Finally, the last Chapter of this Doctoral Thesis includes a summary of the conclusions derived from Chapters III to V.