Idaira Pacheco-Fernández

Are metal-organic frameworks able to provide a new generation of solid-phase microextraction coatings? – A review

Solid-phase microextraction (SPME) is a powerful technique commonly used in sample preparation for extraction/preconcentration of analytes from a wide variety of samples. Among the trends in improving SPME applications, current investigations are focused on the development of novel coatings able to improve the extraction efficiency, sensitivity, and thermal and mechanical stability, within other properties, of current commercial SPME fibers. Metal-organic frameworks (MOFs) merit to be highlighted as promising sorbent materials in SPME schemes. MOFs are porous hybrid materials composed by metal ions and organic linkers, presenting the highest surface areas known, with ease synthesis and high tuneability, together with adequate chemical and thermal stability. For MOF based-SPME fibers, it results important to pretreat adequately the SPME supports to ensure the correct formation of the MOF onto the fiber or the attachment MOF-support. This, in turn, will increase the final stability of the fiber while generating uniform coatings. This review provides a critical overview of the current state of the use of MOFs as SPME coatings, not only highlighting the advantages of these materials versus commercial SPME coatings in terms of stability, selectivity, and sensitivity; but also insightfully describing the current methods to obtain reproducible MOF-based SPME coatings.

Utilization of highly robust and selective crosslinked polymeric ionic liquid-based sorbent coatings in direct-immersion solid-phase microextraction and high-performance liquid chromatography for determining polar organic pollutants in waters.

Several crosslinked polymeric ionic liquid (PIL)-based sorbent coatings of different nature were prepared by UV polymerization onto nitinol wires. They were evaluated in a direct-immersion solid-phase microextraction (DI-SPME) method in combination with high-performance liquid chromatography (HPLC) and diode array detection (DAD). The studied PIL coatings contained either vinyl alkyl or vinylbenzyl imidazolium-based (ViCnIm- or ViBCnIm-) IL monomers with different anions, as well as different dicationic IL crosslinkers. The analytical performance of these PIL-based SPME coatings was firstly evaluated for the extraction of a group of 10 different model analytes, including hydrocarbons and phenols, while exhaustively comparing the performance with commercial SPME fibers such as polydimethylsyloxane (PDMS), polyacrylate (PA) and polydimethylsiloxane/divinylbenzene (PDMS/DVB), and using all fibers under optimized conditions. Those fibers exhibiting a high selectivity for polar compounds were selected to carry out an analytical method for a group of 5 alkylphenols, including bisphenol-A (BPA) and nonylphenol (n-NP). Under optimum conditions, average relative recoveries of 108% and inter-day precision values (3 non-consecutive days) lower than 19% were obtained for a spiked level of 10µgL(-1). Correlations coefficients for the overall method ranged between 0.990 and 0.999, and limits of detection were down to 1µgL(-1). Tap water, river water, and bottled water were analyzed to evaluate matrix effects. Comparison with the PA fiber was also performed in terms of analytical performance. Partition coefficients (logKfs) of the alkylphenols to the SPME coating varied from 1.69 to 2.45 for the most efficient PIL-based fiber, and from 1.58 to 2.30 for the PA fiber. These results agree with those obtained by the normalized calibration slopes, pointing out the affinity of these PILs-based coatings.

Guanidinium ionic liquid-based surfactants as low cytotoxic extractants: Analytical performance in an in-situ dispersive liquid–liquid microextraction method for determining personal care products

The IL-based surfactant octylguanidinium chloride (C8Gu-Cl) was designed and synthetized with the purpose of obtaining a less harmful surfactant: containing guanidinium as core cation and a relatively short alkyl chain. Its interfacial and aggregation behavior was evaluated through conductivity and fluorescence measurements, presenting a critical micelle concentration value of 42.5 and 44.6mmolL-1, respectively. Cytotoxicity studies were carried out with C8Gu-Cl and other IL-based and conventional surfactants, specifically the analogue 1-octyl-3-methylimidazolium chloride (C8MIm-Cl), and other imidazolium- (C16MIm-Br) and pyridinium- (C16Py-Cl) based surfactants, together with the conventional cationic CTAB and the conventional anionic SDS. From these studies, C8Gu-Cl was the only one to achieve the classification of low cytotoxicity. An in situ dispersive liquid-liquid microextraction (DLLME) method based on transforming the water-soluble C8Gu-Cl IL-based surfactant into a water-insoluble IL microdroplet via a simple metathesis reaction was then selected as the extraction/preconcentration method for a group of 6 personal care products (PCPs) present in cosmetic samples. The method was carried out in combination with high-performance liquid chromatography (HPLC) and diode array detection (DAD). The method was properly optimized, requiring the use of only 30μL of C8Gu-Cl for 10mL of aqueous sample with a NaCl content of 8% (w/v) to adjust the ionic strength and pH value of 5. The metathesis reaction required the addition of the anion exchange reagent (bis[(trifluoromethyl)sulfonyl]imide - 1:1 molar ratio), followed by vortex and centrifugation, and dilution of the final microdroplet up to 60μL with acetonitrile before the injection in the HPLC-DAD system. The optimum in situ DLLME-HPLC-DAD method takes ∼10min for the extraction step and ∼22min for the chromatographic separation, with analytical features of low detection limits: down to 0.4μgL-1; high reproducibility: with RSD values lower than 10% (intra-day) and 16% (inter-day) for a spiked level of 15μgL-1; and an average enrichment factor of 89. The requirement of low volumes (30μL) of a low cytotoxic IL-based surfactant allows the method to be considered less harmful than other common analytical microextraction approaches.

Salt-induced ionic liquid-based microextraction using a low cytotoxic guanidinium ionic liquid and liquid chromatography with fluorescence detection to determine monohydroxylated polycyclic aromatic hydrocarbons in urine

AbstractA novel ionic liquid (IL)-based microextraction method has been developed for the determination of four hydroxylated polycyclic aromatic hydrocarbons (OHPAHs) in urine samples. The water soluble IL-based surfactant selected as extraction solvent is decylguanidinium chloride (C10Gu-Cl), the cytotoxicity and micellar behavior of which were evaluated. The proposed salt-induced IL-based preconcentration method simply consists in adding NaClO4 to the aqueous medium containing the IL to promote its water insolubility. The entire method was optimized, requiring the use of only 20 μL of C10Gu-Cl for 10 mL of diluted urine sample (1:10) without any pH adjustment, followed by the addition of NaClO4 to ensure a 5% (w/v) content. A cloudy solution was observed immediately, and after the application of 4 min of vortex and 8 min of centrifugation, the droplet was diluted up to 60 μL with a mixture of acetonitrile:water (30:70) and injected into the liquid chromatograph with fluorescence detection. The method was validated using both synthetic urine and human urine as matrix for the determination of the four OHPAHs. The following analytical features were obtained: detection limits down to 1 ng·L-1 in real urine; inter-day reproducibility (as RSD in %) always lower than 17% when dealing with real urine samples spiked at 80 ng·L-1; and average relative recoveries of 102% in real urine samples at such low spiked levels. Despite the simplicity of the proposed method, it performed successfully with complex urine samples. Graphical abstractSalt-induced IL-based microextraction using a low cytotoxic IL for mono-OHPAHs in urine

Monitoring trihalomethanes in chlorinated waters using a dispersive liquid–liquid microextraction method with a non-chlorinated organic solvent and gas chromatography–mass spectrometry

ABSTRACT The environmental monitoring of trihalomethanes (THMs) has been performed by setting up a dispersive liquid–liquid microextraction method in combination with gas chromatography (GC)–mass spectrometry (MS). The optimized method only requires ∼26 µL of decanol as extractant solvent, dissolved in ∼1 mL of acetone (dispersive solvent) for 5 mL of the environmental water containing THMs. The mixture is then subjected to vortex for 1 min and then centrifuged for 2 min at 3500 rpm. The microdroplet containing the extracted THMs is then sampled with a micro-syringe, and injected (1 µL) in the GC–MS. The method is characterized for being fast (3 min for the entire sample preparation step) and environmentally friendly (low amounts of solvents required, being all non-chlorinated), and also for getting average relative recoveries of 90.2–106% in tap waters; relative standard deviation values always lower than 11%; average enrichment factors of 48–49; and detection limits down to 0.7 µg·L-1. Several waters: tap waters, pool waters, and wastewaters were successfully analyzed with the method proposed. Furthermore, the method was used to monitor the formation of THMs in wastewaters when different chlorination parameters, namely temperature and pH, were varied. GRAPHICAL ABSTRACT

Metallic Coatings in Solid-Phase Microextraction: Environmental Applications

Solid-phase microextraction (SPME) is a non-exhaustive extraction and preconcentration technique based on the partitioning of the compounds present in a sample to a sorbent material. The sorbent material is immobilized onto the surface of a solid support, forming a SPME fiber of roughly 1 cm long and few micrometers of thickness. This microextraction approach is simple, solvent-free, fast, portable, it provides high preconcentration factors, and it can be automated easily. The main disadvantage of SPME is linked to the relatively low number of fibers commercially available, which limits the selectivity and applicability of this extraction method. In this sense, current trends are focused on the development of novel sorbent coatings for SPME. Among novel materials explored up-to-date, metal-based coatings have been successfully exploited in environmental analysis. They are characterized by high mechanical, chemical and thermal stability, ease of preparation and enhanced extraction performance.

A guanidinium ionic liquid-based surfactant as an adequate solvent to separate and preconcentrate cadmium and copper in water using in situ dispersive liquid–liquid microextraction

An in situ dispersive liquid–liquid microextraction (DLLME) method together with flame atomic absorption spectroscopy (FAAS) is developed for the extraction and determination of copper and cadmium from aqueous samples using as an extraction solvent a low cytotoxic ionic liquid (IL)-based surfactant, specifically decylguanidinium chloride (C10Gu-Cl). The IL-based surfactant 1-hexadecyl-3-butylimidazolium bromide (C16C4Im-Br) is also used for comparative purposes. In the method, N,N′-bis(salicylidene)thiocarbohydrazide is the complexing agent, and the metathesis reaction in the in situ DLLME is accomplished using lithium bis[(trifluoromethyl)sulfonyl]imide. The main parameters affecting the extraction efficiency of the method, i.e. pH of the sample, NaCl content, and vortex time, are properly optimized with a Doehlert experimental design. The method using C10Gu-Cl exhibited a limit of detection (LOD) four times lower and with slightly better reproducibility than that of the imidazolium IL-based surfactant. The validation of the in situ DLLME-FAAS method with C10Gu-Cl is accomplished for the simultaneous extraction and quantification of copper and cadmium from water. The optimum method requires 10 mL of aqueous sample and ∼25 μL of the IL-based surfactant to obtain a microdroplet of ∼21 μL, which is diluted up to 120 μL with acetonitrile to perform the analytical determination of both metals. LODs down to 0.3 and 0.5 μg L−1 were reached with the entire in situ IL-DLLME-FAAS for copper and cadmium, respectively. The inter-day relative standard deviation values were lower than 17% for both metal ions; with relative recoveries of 97.8% and 102%, and enrichment factors of 85 and 94, for copper and cadmium, respectively, at a low spiked level (4 and 6 μg L−1, respectively). Furthermore, the developed method shows adequate precision and accuracy evaluated with a certified reference material, the absence of matrix effects, and high tolerance limits towards common cations (between 80 and 600) for the analysis of tap water, while accomplishing the requirements of green analytical chemistry.

CHAPTER 3:Ionic Liquid-based Surfactants: A Step Forward

Ionic liquid-based surfactants are a group of ionic liquid derivatives capable of forming micellar aggregates when dissolved in water above a certain concentration, known as the critical micelle concentration (CMC). This new class of surfactants was initially obtained by incorporating long alkyl chain substituents within the charged cationic group of conventional monocationic IL structures. More recently, dicationic, tricationic, and functionalized IL-based surfactants have been described. IL-based surfactants present great tuneability as original ILs: simple modifications in their structures produce important variations in their micellar properties. Furthermore, micelles formed by IL-based surfactants exhibit lower CMC values than conventional cationic surfactants when comparing similar structures. It is important to characterize the micellization and interfacial behaviour of IL-based surfactants in order to apply them successfully in specific fields. Several techniques can be used for such characterization, such as surface tension, fluorescence and conductivity measurements. Due to their structural versatility and singular properties, IL-based surfactants have generated a great deal of interest, which is reflected in the increasing number of applications that have been reported in recent years. Among the main applications of IL-based surfactants, worthy of mention are biomedicine, catalysis, solvents, nanotechnology, and separation science fields.