Evaluation of Structurally Different Ionic Liquid-Based Surfactants in a Green Microwave-Assisted Extraction for the Flavonoids Profile Determination of Mangifera sp. and Passiflora sp. Leaves from Canary Islands.

Aqueous solutions of ionic liquids (ILs) with surface active properties were used as extraction solvents, taking advantage of their impressive solvation properties, in a green microwave-assisted solid-liquid extraction method (IL-MA-SLE) for the extraction of flavonoids from passion fruit and mango leaves. The extraction method was combined with high-performance liquid chromatography and photodiode-array detection (HPLC-PDA) and optimized by response surface methodology using the Box-Behnken experimental design. Under optimum conditions, the extraction efficiency of six structurally different IL-based surfactants was evaluated. Thus, imidazolium-, guanidinium- and pyridinium-type ILs with different tailorable characteristics, such as side chain length and multicationic core, were assessed. The decylguanidinium chloride ([C10Gu+][Cl-]) IL-based surfactant was selected as key material given its superior performance and its low cytotoxicity, for the determination of flavonoids of several samples of Passiflora sp. and Mangifera sp. leaves from the Canary Islands, and using as target analytes: rutin, quercetin and apigenin. The analysis of 50 mg of plant material only required 525 µL of the low cytotoxic IL-based surfactant solution at 930 mM, 10.5 min of microwave irradiation at 30 °C and 50 W, which involves a simpler, faster, more efficient and greener method in comparison with other strategies reported in the literature for obtaining bioactive compounds profiles from plants.

Mixed Functionalization of Organic Ligands in UiO-66: A Tool to Design Metal-Organic Frameworks for Tailored Microextraction.

The mixed-ligand strategy was selected as an approach to tailor a metal-organic framework (MOF) with microextraction purposes. The strategy led to the synthesis of up to twelve UiO-66-based MOFs with different amounts of functionalized terephthalate ligands (H-bdc), including nitro (-NO2) and amino (-NH2) groups (NO2-bdc and NH2-bdc, respectively). Increases of 25% in ligands were used in each case, and different pore environments were thus obtained in the resulting crystals. Characterization of MOFs includes powder X-ray diffraction, infrared spectroscopy, and elemental analysis. The obtained MOFs with different degrees and natures of functionalization were tested as sorbents in a dispersive miniaturized solid-phase extraction (D-µSPE) method in combination with high-performance liquid chromatography (HPLC) and diode array detection (DAD), to evaluate the influence of mixed functionalization of the MOF on the analytical performance of the entire microextraction method. Eight organic pollutants of different natures were studied, using a concentration level of 5 µg· L-1 to mimic contaminated waters. Target pollutants included carbamazepine, 4-cumylphenol, benzophenone-3, 4-tert-octylphenol, 4-octylphenol, chrysene, indeno(1,2,3-cd)pyrene, and triclosan, as representatives of drugs, phenols, polycyclic aromatic hydrocarbons, and disinfectants. Structurally, they differ in size and some of them present polar groups able to form H-bond interactions, either as donors (-NH2) or acceptors (-NO2), permitting us to evaluate possible interactions between MOF pore functionalities and analytes' groups. As a result, extraction efficiencies can reach values of up to 60%, despite employing a microextraction approach, with four main trends of behavior being observed, depending on the analyte and the MOF.

Application of a Pillared-Layer Zn-Triazolate Metal-Organic Framework in the Dispersive Miniaturized Solid-Phase Extraction of Personal Care Products from Wastewater Samples.

The pillared-layer Zn-triazolate metal-organic framework (CIM-81) was synthesized, characterized, and used for the first time as a sorbent in a dispersive micro-solid phase extraction method. The method involves the determination of a variety of personal care products in wastewaters, including four preservatives, four UV-filters, and one disinfectant, in combination with ultra-high performance liquid chromatography and UV detection. The CIM-81 MOF, constructed with an interesting mixed-ligand synthetic strategy, demonstrated a better extraction performance than other widely used MOFs in D-µSPE such as UiO-66, HKUST-1, and MIL-53(Al). The optimization of the method included a screening design followed by a Doehlert design. Optimum conditions required 10 mg of CIM-81 MOF in 10 mL of the aqueous sample at a pH of 5, 1 min of agitation by vortex and 3 min of centrifugation in the extraction step; and 1.2 mL of methanol and 4 min of vortex in the desorption step, followed by filtration, evaporation and reconstitution with 100 µL of the initial chromatographic mobile phase. The entire D-µSPE-UHPLC-UV method presented limits of detection down to 0.5 ng·mL-1; intra-day and inter-day precision values for the lowest concentration level (15 ng·mL-1)-as a relative standard deviation (in %)-lower than 8.7 and 13%, respectively; average relative recovery values of 115%; and enrichment factors ranging from ~3.6 to ~34. The reuse of the CIM-81 material was assessed not only in terms of maintaining the analytical performance but also in terms of its crystalline stability.

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.

A 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 abstract Salt-induced IL-based microextraction using a low cytotoxic IL for mono-OHPAHs in urine.

Influence of Ligand Functionalization of UiO-66-Based Metal-Organic Frameworks When Used as Sorbents in Dispersive Solid-Phase Analytical Microextraction for Different Aqueous Organic Pollutants.

Four metal-organic frameworks (MOFs), specifically UiO-66, UiO-66-NH2, UiO-66-NO2, and MIL-53(Al), were synthesized, characterized, and used as sorbents in a dispersive micro-solid phase extraction (D-µSPE) method for the determination of nine pollutants of different nature, including drugs, phenols, polycyclic aromatic hydrocarbons, and personal care products in environmental waters. The D-µSPE method, using these MOFs as sorbents and in combination with high-performance liquid chromatography (HPLC) and diode-array detection (DAD), was optimized. The optimization study pointed out to UiO-66-NO2 as the best MOF to use in the multi-component determination. Furthermore, the utilization of isoreticular MOFs based on UiO-66 with the same topology but different functional groups, and MIL-53(Al) to compare with, allowed us for the first time to evaluate the influence of such functionalization of the ligand with regards to the efficiency of the D-µSPE-HPLC-DAD method. Optimum conditions included: 20 mg of UiO-66-NO2 MOF in 20 mL of the aqueous sample, 3 min of agitation by vortex and 5 min of centrifugation, followed by the use of only 500 µL of acetonitrile as desorption solvent (once the MOF containing analytes was separated), 5 min of vortex and 5 min of centrifugation. The validation of the D-µSPE-HPLC-DAD method showed limits of detection down to 1.5 ng·L-1, average relative recoveries of 107% for a spiked level of 1.50 µg·L-1, and inter-day precision values with relative standard deviations lower than 14%, for the group of pollutants considered.

Double salts of ionic-liquid-based surfactants in microextraction: application of their mixed hemimicelles as novel sorbents in magnetic-assisted micro-dispersive solid-phase extraction for the determination of phenols.

The use of mixed hemimicelles of ionic liquid (IL)-based surfactants in a magnetic-based micro-dispersive solid-phase extraction (m-µdSPE) approach is described. Not only is the symmetric monocationic IL-based surfactant 1,3-didodecylimidazolium bromide (C12C12Im-Br) studied for first time in m-µdSPE, but double-salt (DS) IL (DSIL)-based surfactants are also examined. Nine DSIL-based surfactants were formed by combination of C12C12Im-Br with other IL-based surfactants, including nonsymmetric monocationic and dicationic ILs combined at three different molar fractions. The analytical application was focused on the determination of a group of eight phenols, including bisphenol A, in water samples. The best results were obtained with the DSIL formed by C12C12Im-Br (molar fraction 0.5) and 1-hexadecyl-3-methylimidazolium bromide (C16MIm-Br), after proper optimization of the overall method in combination with high-performance liquid chromatography (HPLC) and diode-array detection (DAD). The optimum conditions for 100 mL of water samples require a small amount (10 mg) of Fe3O4 magnetic nanoparticles, a low content (5.0 mg of C12C12Im-Br and 3.9 mg of C16MIm-Br) of the selected DSIL, pH 11, a sonication time of 2.5 min, and an equilibration time of 5 min with the aid of NdFeB magnets, followed by elution of phenols, evaporation, and reconstitution with 0.5 mL of acetonitrile. The overall m-µdSPE-HPLC-DAD method is characterized for limits of detection down to 1.3 µg · L(-1), intraday relative standard deviations lower than 13 % (n = 3), and interday relative standard deviations lower than 17 % (n = 9), with a spiking level of 15 µg · L(-1); with enrichment factors between 15.7 and 141, and average relative recoveries of 99.9 %.

Utilization of an ionic liquid in situ preconcentration method for the determination of the 15 + 1 European Union polycyclic aromatic hydrocarbons in drinking water and fruit-tea infusions.

An ionic liquid (IL) in situ preconcentration method was optimized and applied to the monitoring of the 15 + 1 European Union polycyclic aromatic hydrocarbons in water and fruit-tea infusions. The optimized method utilizes 10 mL of water (or infusion) containing 38 µL of the IL 1-butyl-3-methylimidazolium chloride and a content of 36.1 g/L NaCl, which are mixed with Li-NTf2 (340 µL, 0.2 g/mL), followed by vortex (4 min) and centrifugation (5 min). The obtained microdroplet containing hydrocarbons is diluted with acetonitrile and injected into an HPLC with UV/Vis and fluorescence detection. The method presented average enrichment factors of 127 for water (tap water and bottled water) and 27 for two fruit-tea infusions; with average relative recoveries of 86.7 and 106% for water and fruit-tea infusions, respectively. The method was sensitive, with detection limits ranging from 0.001 to 0.050 ng/mL in water, and from 0.010 to 0.600 ng/mL in fruit-tea infusions, for the fluorescent hydrocarbons. Real extraction efficiencies ranged from 12.7 to 58.7% for water, and from 20.2 to 117% for the infusions. The method was also fast (~12 min) and free of organic solvents in the extraction step.

A green miniaturized aqueous biphasic system prepared with cholinium chloride and a phosphate salt to extract and preconcentrate personal care products in wastewater samples.

A miniaturized extraction/preconcentration method based on an aqueous biphasic system (µ-ABS) was developed with reagents commonly used as food additives: cholinium chloride (ChCl) as main extraction phase, K2HPO4 as salting-out agent, and water as the main component (being the sample for analyses). With the aim of obtaining high enrichment factors, miniaturization, and adequate analytical performance, a point in the biphasic region with the lowest amount of ChCl was selected, corresponding to 1.55% (w/w) of ChCl, 59.5% (w/w) of K2HPO4, and 38.95% (w/w) of water. The green µ-ABS (attending to its main elements and performance mode) was used in combination with high-performance liquid chromatography with diode-array detection (HPLC-DAD) for the determination of 9 personal care products in wastewater samples. The µ-ABS-HPLC-DAD method showed high enrichment factors (up to 100), and quantitative extraction efficiencies for those compounds containing OH groups in their structure, which can undergo hydrogen bonding with ChCl. Thus, limits of quantification down to 0.8 µg·L-1 and extraction efficiencies between 66.4 and 108% (concentration levels of 1.3 and 13 µg·L-1) were reached for the group of parabens and the UV-filter benzophenone-3. The method is characterized by the use of non-harmful reagents and the absence of organic solvents in the entire sample preparation procedure, while being simple, low-cost, easily compatible with HPLC, and highly efficient.

Headspace solid-phase microextraction based on the metal-organic framework CIM-80(Al) coating to determine volatile methylsiloxanes and musk fragrances in water samples using gas chromatography and mass spectrometry.

A headspace solid-phase microextraction (HS-SPME) method was developed using the metal-organic framework (MOF) CIM-80(Al) as extraction phase and in combination with gas chromatography-mass spectrometry (GC-MS) for the simultaneous determination of 6 methylsiloxanes and 7 musk fragrances in different environmental waters. The chromatographic separation was optimized in different GC instruments equipped with different detectors, allowing the correct separation and identification of the compounds. The HS-SPME method was optimized using a Box-Behnken experimental design, while the validation was carried out together with the most suitable commercial fiber (divinylbenzene/polydimethylsiloxane) for comparison purposes. The MOF-based coating was particularly efficient for the determination of volatile methylsiloxanes, showing moderately lower limits of detection (of 0.2 and 0.5 µg L-1versus 0.6 µg L-1 for cyclic methylsiloxanes) and slightly better precision (relative standard deviation values lower than 17% versus 22%) than the commercial coating, while avoiding the cross-contamination issues associated to the polymeric composition of commercial fibers. The method was applied for the analysis of seawater and wastewater samples, allowing the quantification of several analytes and the assessment of matrix effects. The proposed HS-SPME method using the CIM-80(Al) fiber constitutes a more environmentally friendly, simpler, and efficient strategy in comparison with other sample preparation methods using different extraction techniques, while the use of a MOF as fiber sorbent constitutes a potential alternative to exploit the features of SPME for the challenging environmental monitoring of these compounds.

Insights into Paraben Adsorption by Metal-Organic Frameworks for Analytical Applications.

Metal-organic frameworks (MOFs) are attractive materials used as sorbents in analytical microextraction applications for contaminants of emerging concern (CECs) from environmental liquid matrices. The demanding specs for a sorbent in the analytical application can be comprehensively studied by considering the interactions of the target analytes with the frameworks by the use of single-crystal X-ray diffraction, computational analysis, and adsorption studies, including the kinetic ones. The current study intends a better understanding of the interactions of target CECs (particularly, propylparaben (PPB) as a model) and three Zn-based layered pillared MOFs: CIM-81 [Zn2(tz)2(bdc)] (Htz = 1,2,4-triazole and H2bdc = 1,4-benzenedicarboxylic acid) and their amino derivatives [Zn2(NH2-tz)2(bdc)] CIM-82 and [Zn2(tz)2(NH2-bdc)] CIM-83 (NH2-Htz = 3-amino-1,2,4-triazole and NH2-H2bdc = 2-amino-1,4-benzenedicarboxylic acid). The crystal structures of the two solvate compounds (dma@CIM-81 (dma = dimethylacetamide) and acetone@CIM-81) were solved by single-crystal X-ray diffraction to determine the points of interaction between the framework and the guest molecules. They also served as a starting point for the computational modeling of the PPB@CIM-81 compound, showing that up to two PPB molecules can be hosted in one of the pores, while only one can be trapped in the second pore type, leading to a maximum theoretical capacity of 291.9 mg g-1. This value is close to the value obtained by the adsorption isotherm experiment for CIM-81 (283 mg g-1). This value is, by far, higher than those previously reported for other materials for the removal of PPB from water, and also higher than the experimental values obtained for CIM-82 (54 mg g-1) and CIM-83 (153 mg g-1). The kinetics of adsorption is not very fast, with uptake of about 40% in 3 h, although a 70% release in methanol is achieved in 1 h. In addition, a further comparison of performance in analytical microextraction (requiring only 10 mg of CIM-81) was carried out together with chromatographic analysis to support all insights attained, with the method being able to monitor CECs as low as µg L-1 levels in complex environmental water samples, thus performing successfully for water monitoring even in multicomponent scenarios.

Suitability of ionic liquids as mobile-phase additives in HPLC with fluorescence and UV detection for the determination of heterocyclic aromatic amines.

The effects of several ionic liquids (ILs) as mobile-phase additives in HPLC with fluorescence and UV-Vis detection for the determination of six heterocyclic aromatic amines were evaluated using two different C(18) stationary phases with moderate silanol activity. The studied ILs were 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate and 1-methyl-3-octylimidazolium tetrafluoroborate. The optical behaviour of heterocyclic aromatic amines in presence of ILs was studied and the silanol-suppressing potency of ILs was evaluated for the two stationary phases studied. Several chromatographic parameters were evaluated in the presence or absence of ILs, or using triethylamine, the most common mobile-phase additive. The best results were achieved using 1 mM 1-butyl-3-methylimidazolium tetrafluoroborate as mobile-phase additive and NovaPak column. In these conditions and with 18% of ACN in the mobile phase, analytical performance of the chromatographic methods using fluorescence and UV-Vis were evaluated, obtaining good precision in all cases (RSD lower than 6.6%) and low LOD (0.001-0.147 microg/mL with UV-Vis and 0.001-0.006 ng/mL with fluorescence detection).

Green solid-phase microextraction fiber coating based on the metal-organic framework CIM-80(Al): Analytical performance evaluation in direct immersion and headspace using gas chromatography and mass spectrometry for the analysis of water, urine and brewed coffee.

A new solid-phase microextraction (SPME) fiber coating was prepared by the immobilization of the metal-organic framework (MOF) CIM-80(Al) on nitinol wires by a green in situ growth approach, using an aqueous synthetic approach, and without the need of any additional material to ensure the attachment of the MOF to the nitinol support. The coating was used for the development of headspace (HS) and direct immersion (DI) SPME methods in combination with gas chromatography and mass spectrometry (GC-MS) for the determination of polycyclic aromatic hydrocarbons (PAHs) as model compounds. Both methods were optimized and validated using the MOF-based fiber together with the commercial polydimethylsiloxane (PDMS) fiber. The MOF extraction phase exhibited superior analytical performance for most of the PAHs in HS-SPME mode (and particularly for less volatiles), while the PDMS fiber presented better results in the DI-SPME method. The analytical performance of the MOF sorbent coating in HS- and DI-SPME methods was also evaluated in urine and brewed coffee samples, without requiring any pretreatment step apart from dilution for DI-SPME experiments, thus showing suitability of the novel coatings for the analysis of complex samples. The proposed CIM-80(Al) fiber was efficient and biocompatible (for using a low cytotoxic sorbent and a biocompatible core support), and it also demonstrated stability and robustness, with inter-fiber (and inter-day) relative standard deviation values lower than 19%, and reusability for more than 80 extraction cycles using 280 °C as desorption temperature.

Use of a pH-sensitive polymer in a microextraction and preconcentration method directly combined with high-performance liquid chromatography.

A pH-sensitive polymer based on the poly(styrene-alt-maleic anhydride) co-polymer serves as basis to develop a microextraction method (pH-HGME) in direct combination with high-performance liquid chromatography (HPLC) and fluorescence detection (FD) for the determination of seven organic compounds, including three polycyclic aromatic hydrocarbons (PAHs), three monohydroxylated PAHs and one alkylphenol, in urine. The method bases on the structural modification of the pH-sensitive polymer in the aqueous sample at a high pH value, followed by the formation and insolubilization of a hydrogel containing the preconcentrated analytes by decreasing the pH, and the direct injection of the hydrogel-rich phase in the HPLC-FD system. The optimization of the main variables permitted the selection of low amounts of aqueous sample (10 mL), which was mixed with 10 mg of co-polymer also present in a low volume (150 µL) of concentrated NaOH. The method further requires the addition of 200 µL of concentrated HCl, 3 min of stirring, and 15 min of centrifugation. This pH-HGME-HPLC-FD method presented low limits of detection, ranging from 0.001 µg L-1 to 0.09 µg L-1 in ultrapure water, average relative recoveries of 96.9% for the concentration level of 0.60 µg L-1, and enrichment factors between 1.50 and 17.7. The proposed method also exhibited high precision, with intermediate relative standard deviations lower than 16% for a concentration level of 0.60 µg L-1. The developed pH-HGME-HPLC-FD method performed adequately when analyzing two human urine samples provided by a non-smoker male and a smoker female, respectively. One of the target analytes (2-hydroxynaphthalene) was quantified in both samples using the standard addition method, with a predicted concentration of 7.3 ± 0.4 µg L-1 in the non-smoker male urine and 19.3 ± 0.6 µg L-1 in the smoker female urine.

Solid-phase microextraction coatings based on the metal-organic framework ZIF-8: Ensuring stable and reusable fibers.

Chemical vapor deposition of MOFs (MOF-CVD) has been used to coat solid-phase microextraction (SPME) fibers with ZIF-8, by exposing ZnO layers to the linker vapor (2-methylimidazole). This ZIF-8 coating has been used as a seed layer in a following solvothermal MOF growth step in order to increase the ZIF-8 thickness. The combined MOF-CVD and solvothermal growth of ZIF-8 on the fibers result in a thickness of ~3 µm, with adequate thermal stability, and mechanical integrity when tested with methanol and acetonitrile ultrasonic treatments. The fibers have been evaluated in direct immersion mode using gas chromatography and flame ionization detection (GC-FID), for a group of target analytes including three polycyclic aromatic hydrocarbons (PAHs) and five personal care products (PCPs). The optimized conditions of the SPME-GC-FID methods include low amount of aqueous sample (5 mL), stirring for 45 min at 35 °C, and desorption at 280 °C for 5 min. The method presents limits of detection down to 0.6 µg L-1; intra-day, inter-day and inter-batch relative standard deviation values lower than 16%, 19%, and 23%, respectively; and a lifetime higher than 70 cycles.

Ionic liquids as desorption solvents and memory effect suppressors in heterocyclic aromatic amines determination by SPME-HPLC fluorescence.

The beneficial effects of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF(4)) ionic liquid (IL) as mobile phase additive, desorption solvent, and memory effect suppressor in solid-phase microextraction (SPME)-high-performance liquid chromatography with fluorescence detection for the determination of six heterocyclic aromatic amines have been evaluated for the first time. Several chromatographic parameters have been evaluated in the presence or absence of IL or using triethylamine as the most common mobile phase additive, with a Nova-Pak C18 stationary phase. This IL was found to be clearly superior to triethylamine for efficiency as well as peak shape enhancement and sensitivity increase. SPME was chosen because it is faster than conventional extraction techniques and allowed us to minimize the use of organic solvents. However, memory effect may become a problem when a high-sensitivity detector is used. The appropriate conditions for the desorption step and to eliminate the memory effect involving BMIm-BF(4) were established and optimized. The method was applied for the determination of these compounds in commercial meat extracts.

Determination of carbonyl compounds in smoke samples: strategies for sampling and standardization.

There are significant drawbacks to the calibration procedure recommended in the normalized Spanish or American methods used to determine carbonyl compounds in ambient air by quantifying hydrazones that form with 2,4-dinitrophenylhydrazine. The impurities present in 2,4-dinitrophenylhydrazine, as well as the lack of quantitativity and the slow kinetics of some derivatization reactions can lead to considerable errors in quantification. This work proposes two alternative systems for sampling biomass smoke in order to analyze aldehydes and ketones. The standardization process used by both systems requires standard solutions to be reacted with 2,4-dinitrophenylhydrazine under experimental conditions similar to those used to collect the sample. The resulting calibration curve slopes differ between 8% and 74% from the curves used in methods that employ commercial standard hydrazone solutions. The detection limits reached by using the proposed methods are between 0.07 and 0.47 mg L(-1). Both methods are complementary for smoke samples that have significant differences in the concentrations of aldehydes or ketones.

Ionic liquid-based miniaturized aqueous biphasic system to develop an environmental-friendly analytical preconcentration method.

Two ILs containing guanidinium cations (butylguanidinium chloride -C4Gu-Cl- and hexylguanidinium chloride -C6Gu-Cl-) were synthesized and characterized. Their cytotoxicity was also assessed, obtaining adequate CC50 values of 680 ±â€¯99 mg·L-1 for C4Gu-Cl and 135 ±â€¯8 mg·L-1 for C6Gu-Cl. Miniaturized aqueous biphasic systems (µ-ABSs) were developed using amounts lower than 1% (w/w) of these synthesized guanidinium-based ILs, K3PO4 as salting-out agent, and ultrapure water. The phases diagrams of both systems were determined, and the C4Gu-Cl-based µ-ABS was selected for the development of a microextraction method in combination with high performance liquid chromatography (HPLC) with fluorescence detection (FD) for the determination of five polycyclic aromatic hydrocarbons (PAHs) as model analytes. A point of the biphasic region of the C4Gu-Cl-based µ-ABS corresponding to a mixture of 0.75% (w/w) of the IL, 37.7% (w/w) of K3PO4 and 61.55% (w/w) of ultrapure water, and 30 min of equilibrium time, were selected as optimum conditions to obtain high enrichment factors and proper analytical microextraction performance. The C4Gu-Cl-based µ-ABS-HPLC-FD method exhibited low limits of detection, between 0.010 ng·L-1 and 2.0 ng·L-1, average relative recoveries of 96.7%, high enrichment factors ranging from 44.1 to 60.4, average extraction efficiencies of 61.7%, and intermediate precision relative standard deviations lower than 17% for a concentration level of 12 ng·L-1. The developed method was applied successfully in the analysis of different tap water samples.

The ionic liquid 1-hexadecyl-3-methylimidazolium bromide as novel extracting system for polycyclic aromatic hydrocarbons contained in sediments using focused microwave-assisted extraction.

A method to extract PAHs from sediments is carried out using aqueous solutions containing aggregates of the ionic liquid (IL) 1-hexadecyl-3-methylimidazolium bromide (HDMIm-Br) as the extracting medium. Focused microwave-assisted extraction has been used to accelerate the extraction step, followed by HPLC with fluorescence detection without clean-up steps to remove the IL prior to injection. The method has been applied to certified reference sediment BCR-535 and marine sediments from Tenerife (Canary Islands) with successful results. The optimized method gave average absolute recoveries of 91.1% for six of the seven PAHs studied, with relative standard deviations lower than 10.4%. The overall method is characterized for presenting low extraction times (6min), low amounts of the sediment (0.1g), low amounts of IL (45mM), and low volumes of aqueous extractant solution (9mL). The use of small amounts of both IL and aqueous extractant solution allows the method to be considered environmental-friendly.

Micelle-mediated extractions using nonionic surfactant mixtures and HPLC-UV to determine endocrine-disrupting phenols in seawaters.

An environmentally friendly method to extract endocrine-disrupting phenols (EDPs) from seawaters was realized using nonionic surfactant mixtures and micelle-mediated extractions. The preconcentration step was achieved directly in the seawater matrix, and was followed by high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection without any clean-up steps to remove the surfactant mixture prior to injection. Various nonionic surfactant mixtures were used, and polyoxyethylene-10-laurylether (POLE) with polyoxyethylene-4-laurylether (Brij 30) was found to be the best to work with. Method optimization involved maximizing the preconcentration factor using the studied mixtures. The proposed method gave extraction recoveries ranging from 83.3 to 114.4% for an EDP spiking level of 46.7 microg L(-1), and from 63.4 to 112.4% for a spiking level of 4.7 microg L(-1) for EDPs studied in real seawater matrices, with relative standard deviations of <12.1%. The detection limits of the method varied from 0.18 microg L(-1) for bisphenol A (BPA) to 1.17 microg L(-1) for 4-cumylphenol (4-CP). The method was applied to seawaters from the Canary Islands with successful results.

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.