Monitoring of emerging contaminants in waters using novel microextractive techniques
This Doctoral Thesis focuses on the development of analytical methods under the Green Analytical Chemistry (GAC) requirements for the monitoring of two important group of emerging contaminants in environmental water samples: personal care products (PCPs) and disinfection by-products (DBPs). The developed methods are based on the use of microextraction techniques: liquid-phase microextraction (LPME), dispersive miniaturized solid-phase extraction (D-µSPE), and solid-phase microextraction (SPME). Novel strategies are also explored within the extraction step to improve the performance of the methods following current trends in the Analytical Chemistry research field. Furthermore, novel metal-organic frameworks (MOFs) specifically designed to be successful as sorbents in D-µSPE and SPME are completely characterized, and included successfully in monitoring methods for PCPs. All these methods are combined with gas or liquid chromatography (GC or LC) with different detectors to validate and apply the methodologies to the analysis of real samples. This Doctoral Thesis is divided in five Chapters: I) Introduction, II) Hypothesis and Objectives, III) Experimental, IV) Results and Discussion, and V) Conclusions. General considerations about the importance and current state of the monitoring of emerging contaminants in environmental samples are presented in Chapter I. Next sections in this Chapter deal with the description of the main microextraction approaches, together with the improvements proposed within this topic according to the guidelines of GAC. In this sense, the incorporation of novel materials in microextraction methods are outlined, highlighting the use of MOFs, and the applications of these microextraction advances for the determination of emerging contaminants are detailed. Chapter II describes the main and partial objectives of this Doctoral Thesis. Chapter III includes the experimental section, including the analytes, materials, and instrumentation used in this Doctoral Thesis, together with a description of the optimum procedures and the samples analyzed. In Chapter IV, the results obtained are presented and discussed, while Chapter V includes the summary of the most relevant conclusions derived from Chapter IV. Section 1 of Chapter IV includes the first research line of this Doctoral Thesis, specifically the application of a LPME approach in combination with ultra-high-performance LC (UHPLC) and UV detection for the determination of non-volatiles PCPs in water samples. The vortex-assisted emulsification microextraction method (VAEME) proposed in this study is mainly characterized by its simplicity, good extraction efficiencies, low consumption of organic solvents and short analysis time. VAEME does not require the utilization of any type of organic solvent as dispersive solvent, and it is used for the first time in the monitoring of PCPs. Section 2 of Chapter IV includes the second research line of this Doctoral Thesis: the use of sorbent-based microextraction strategies coupled with chromatographic techniques for the determination of emerging compounds in waters. It is divided in D-µSPE (Section 2.1.) and SPME (Section 2.2.) sub-sections according to the type of microextraction method employed. In Section 2.1., traditional and well-known MOFs (HKUST-1(Cu), MIL-53(Al), and UiO-66(Zr)) are synthesized and prepared (to be further used in a comparison study), while novel MOFs based on pillared-layer structures (named CIM-80s and CIM-90s) are designed to ensure better desorption ability when used in D-µSPE, synthesized and properly characterized. For these new MOFs, adsorption/release, kinetics and computational studies are also carried out in order to gain a better understanding on the nature of interactions established between the target analytes and the MOF, while evaluating the presence of preferential adsorption sites. All these MOFs are applied as sorbents in D-µSPE for the monitoring of several groups of PCPs (UV-filters, preservatives, disinfectants, and insect repellents) in environmental water samples. With the aim of covering a wide range of PCPs with different chemical structures and characteristics, the D-µSPE method is combined first with UHPLC (non-volatile PCPs) and then with GC techniques (semi-volatile and volatile PCPs). Therefore, two analytical methodologies (D-µSPE-UHPLC-UV and D-µSPE-GC-mass spectrometry (MS)) are developed and characterized by the incorporation of new tailorable materials, such as MOFs. Section 2.2. is focused on SPME applications in headspace mode (HS-SPME) using both commercial and MOF-based fibers. Commercial fibers are employed for the extraction and preconcentration of DBPs in treated water samples. The proposed method (HS-SPME-GC-flame ionization detection (FID)) presents proper sensitivity for the monitoring of these emerging contaminants using a fully solvent-free microextraction technique, with good precision and short analysis times. Finally, a MOF-based SPME fiber is evaluated for the monitoring of PCPs (methylsiloxanes and musk fragrances). With this simple HS-SPME-GC-MS method, it was possible to cover in the same extraction method two groups of volatile PCPs with quite different chemical nature for the analysis of several environmental waters. Furthermore, the latter approach not only reports the use of a novel MOF-based stationary phase for this specific analytical application, but also deals with a difficult analytical determination: that of methylsiloxanes (considering their wide presence in the environment and in the laboratory materials, and thus involving high risks of contaminations even when using blanks). All the analytical methods are properly optimized (in most cases using experimental designs). They are also validated in terms of accuracy, precision, sensitivity, and possible matrix effects depending on the type of water sample.