Advances in microextraction techniques using novel materials

Resumen

Current trends in analytical sample preparation focus on the development of novel miniaturized extraction techniques to perform faster, simpler, and more sustainable analysis. Efforts in analytical sample preparation are nowadays even more necessary despite all advances achieved during the last decades in terms of more sensitive analytical instruments, as it is expected for sample preparation additional features of greenness, together with those coming from the need of determining trace analytes in complex samples minimizing the analysis time and the tedious of the processes. The development of these microextraction techniques have been also related to the incorporation of novel materials as extractant phases to substitute conventional commercially available materials. Among the different novel materials, it should be highlighted the utilization of metallic nanoparticles (NPs), and metal-organic frameworks (MOFs), as highly interesting sorbent materials in analytical sample preparation given their high surface to volume ratio (for metallic NPs) or surface area (for MOFs), being these properties directly linked with their impressive adsorption capacity. In this Doctoral Thesis, metallic NPs and MOFs-based sorbents were incorporated as extractant materials attached to a variety of supports/devices in different sorbent-based microextraction techniques: dispersive micro-solid-phase extraction (μ-dSPE), in fiber solid-phase microextraction (SPME), in-tube SPME, and thin-film microextraction (TFME). With respect to metallic NPs, AuNPs and AgNPs were prepared following a bottom-up procedure using alternative reduction agents under mild conditions. These sorbents were synthesized, characterized, and incorporated as novel in-fiber SPME coatings. Besides, a novel braid-SPME support was developed as an alternative to conventional SPME supports. The performance of these fibers was compared to commercially available SPME fibers, observing a higher affinity of the analytes towards the NPs-based coatings. With respect to MOFs, they were (i) used as coating onto the surface of silica microspheres forming core-shell microspheres to be used in μ-dSPE, (ii) attached to the inner walls of fused silica capillaries to be used as open tubular in-tube SPME devices, and (iii) embedded in a polymer for the preparation of MOF-based mixed matrix membranes (MMMs) to be used in TFME. The incorporation of MOFs into these different formats and microextraction techniques allowed to achieve high adsorption and extraction capacity for the determination of target analytes at trace levels in complex samples. The proposed sorbents, devices, and microextraction methods, were combined with chromatographic techniques, with the resulting methods being optimized, validated, and applied to the analysis of real samples, demonstrating their adequate analytical performance. Besides, a green assessment of the proposed methods was performed to discuss the advantages and weaknesses of the sorbent-based microextraction methods developed in this Doctoral Thesis.