Analytical strategies for sample preparation using novel materials

  1. Idaira Pacheco Fernández
Supervised by:
  1. Verónica Pino Estévez Director
  2. Juan H. Ayala Díaz Director

Defence university: Universidad de La Laguna

Year of defence: 2021

Committee:
  1. Maria Soledad Cardenas Aranzana Chair
  2. Javier Hernández Borges Secretary
  3. Emanuela Gionfriddo Committee member

Type: Thesis

Teseo: 650657 DIALNET lock_openRIULL editor

Abstract

Sample preparation is the stage of the analytical procedure that deals with the extraction of the target compounds from a sample and includes the elimination of the interferences coming from the sample matrix, thus ensuring the compatibility with the analytical instrument while improving the selectivity and sensitivity of the entire method. Given the complexity of the samples, the trace concentrations at which analytes are present in the samples, and the importance of incorporating the Green Chemistry principles in the analytical process, the development of microextraction techniques and the incorporation of new materials have been demanding research lines within analytical sample preparation to address these challenges. Among the outstanding materials described that can meet green requirements and exhibit successful analytical performance in sample preparation, ionic liquids (ILs) and metal-organic frameworks (MOFs) must be highlighted. ILs are molten salts formed by the combination of bulky organic cations and organic or inorganic anions. They present melting points lower than 100 °C and, depending on the moieties selected and the incorporation of specific functional groups in their structure, they can exhibit specific characteristics. Therefore, it is possible to prepare several interesting derivatives, such as polymeric ionic liquids (PILs) and IL-based surfactants. MOFs are crystalline materials composed of metallic clusters and organic linkers connected by coordination bonds. They are mainly characterized by their high surface area and tunability, which allows designing MOFs with specific topologies by selecting the adequate components and synthetic conditions. These characteristics make MOFs potential materials to host target compounds. In this Doctoral Thesis, ILs and MOFs were designed, synthesized and incorporated in a wide variety of challenging analytical applications using microextraction techniques. Among the existing techniques, dispersive liquid-liquid microextraction (DLLME) and solid-phase microextraction (SPME) were selected due to their simplicity, fastness, and high preconcentration ability. ILs of low cytotoxicity formed by the combination of monoalkylguanidinium cation and chloride anion were synthesized with different alkyl chain lengths. Their cytotoxicity was evaluated, and the surface-active properties of the ILs with the longer alkyl substituents were also studied. These hydrophilic ILs were used in different DLLME approaches in which a low amount of the ionic liquids is added to the aqueous sample and then insolubilized using different reagents. The use of water-soluble solvents as extraction media improves the dispersion and the efficiency of the extraction. In the first strategies, a metathesis reaction of the IL was used to exchange the anion and obtain the hydrophobic IL droplet containing the target compounds. With the aim of improving the greenness of the method (given the toxicity of the fluorine-containing anion-exchange reagent), the non-harmful NaClO4 salt was used to promote the metathesis reaction and carry out the extraction. The guanidinium-based IL with the lowest cytotoxicity was also used in a microextraction method but based on the aqueous biphasic system formed by water, the IL and K3PO4, with the insolubilization of the IL accomplished due to the salting-out effect exerted by the salt. With respect to SPME applications, functionalized PILs and MOFs were synthesized and used to prepare stable and selective coated-fibers and coated-capillaries to analyze complex samples. Thus, different crosslinked PILs-based coatings were prepared by using functionalized ILs as monomers and dicationic ILs as crosslinker agents to improve the mechanical stability of the resulting polymer. Fibers coated with PILs containing aromatic groups, long alkyl chains, and anions with higher hydrogen bond basicity, exhibited better extraction efficiency towards polar analytes. The use of zwitterionic ILs with high dipole moments as monomers to prepare coated fibers led to enhanced extraction without significant matrix effects in comparison with commercial coatings. Furthermore, PILs composed of IL monomers functionalized with carboxylic groups were evaluated for the selective extraction of DNA using in-tube SPME devices taking advantage of the anion-exchange extraction mechanism of the PIL towards this biomolecule. Regarding the use of crystalline materials in SPME, the MOF CIM-80(Al), formed by mesaconic acid as organic linker and Al (III) as metal, was used to prepare an on-fiber SPME coating. The MOF is synthesized following a simple and green procedure directly on the surface of nitinol wires, thus ensuring the preparation of a neat MOF coating. It also exhibits low cytotoxicity, high thermal stability, surface area, and stability in several matrices, which allowed the use of the device for the analysis of complex aqueous-based samples, including brewed coffee and urine. The reusable device presented adequate precision, efficiency and stability, with comparable results in comparison with commercial coatings. The proposed materials and microextraction methods in combination with chromatographic and spectroscopic techniques were optimized and validated, thus demonstrating to be useful for the analysis of environmental, food and biological samples with satisfactory analytical performance, which allowed the determination of the target analytes at trace concentration levels.