Ionic liquids in dispersive liquid-liquid microextraction

A screen-printed electrode modified with silver nanoparticles and carbon nanofibers in a nafion matrix for ionic liquid-based dispersive liquid-liquid microextraction and voltammetric assay of heterocyclic amine 8-MeIQx in food

An electrochemical method is described for the determination of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (8-MeIQx) which is a heterocyclic aromatic amine formed in cooked food samples. The method uses a screen-printed carbon nanofiber electrode that is modified with silver nanoparticles (AgNPs) in a Nafion matrix. The surface of the modified electrode was characterized by UV-vis spectrometry, dynamic light scattering, scanning electron microscopy and Raman spectroscopy. The average size of the AgNPs is 14 nm. The modified electrode exhibits good properties in terms of reversibility, fast kinetics of electron transfer, and large electroactive area toward the reduction of 8-MeIQx. Differential pulse voltammetry is the most suitable electrochemical technique for quantification of 8-MeIQx, best at a voltage of -0.21 V (versus Ag reference electrode). The first derivative serves as the analytical signal that increases linearly in the 0.015-40 mg L^-1 8-MeIQx concentration range, with a 5 μg L^-1 detection limit. A dispersive liquid-liquid microextraction procedure assisted via ionic liquid was developed to isolate the analyte from real samples. The whole extraction-preconcentration and voltammetric method allows to determine 30 and 70 μg L^-1 in (spiked) bouillon cube, meat broth, beer and wine, with recoveries in the 93.6-110.4% range. Graphical abstractSchematic presentation for the analysis of aromatic amine 8-MeIQx, resultant compound from cooking meat. Extracted sample solution was placed onto modified electrode surface thus obtaining voltammetric analytical signal. So, quantification atrelevant levels can be performed.

Ultrasound for Drug Synthesis: A Green Approach

This last century, the development of new medicinal molecules represents a real breakthrough in terms of humans and animal life expectancy and quality of life. However, this success is tainted by negative environmental consequences. Indeed, the synthesis of drug candidates requires the use of many chemicals, solvents, and processes that are very hazardous, toxic, energy consuming, expensive, and generates a large amount of waste. Many large pharmaceutical companies have thus moved to using green chemistry practices for drug discovery, development, and manufacturing. One of them is the use of energy-efficient activation techniques, such as ultrasound. This review summarizes the latest most representative works published on the use of ultrasound for sustainable bioactive molecules synthesis.

Air-assisted ionic liquid dispersive liquid-liquid microextraction based on solidification of the aqueous phase for the determination of triazole fungicides in water samples by high-performance liquid chromatography

A simple, rapid, and environmentally friendly approach was introduced to determine triazole fungicides in water samples by air-assisted ionic liquid dispersive liquid-liquid microextraction based on solidification of the aqueous phase using high-performance liquid chromatography-diode array detection. Ionic liquid was applied as the extraction solvent rather than a high-toxicity extraction solvent. The air-assisted dispersion method induced a trace amount of the ionic liquid to disperse as small droplets in the water sample, which significantly increased the contact area between the organic phase and the aqueous phase for the rapid transfer of target fungicides without using a dispersion solvent or auxiliary extraction devices. The solidification of the aqueous phase facilitated the collection of extraction solvent. The type of extraction solvent, the volume ratio of the extraction solvent to the water sample, the number of extraction cycles, the addition of NaCl, and pH values were evaluated. The recoveries were 72.65-100.13% with a relative standard deviation of 0.92% to 5.99%. The limits of quantification varied from 0.65 ng mL^-1 to 1.83 ng mL^-1. This approach can be used to determine fungicides in ground, river, and lake water samples.

Extraction of DNA with magnetic ionic liquids using in situ dispersive liquid-liquid microextraction

A new class of magnetic ionic liquids (MILs) with metal-containing cations was applied in in situ dispersive liquid-liquid microextraction (DLLME) for the extraction of long and short double-stranded DNA. For developing the method, MILs comprised of N-substituted imidazole ligands (with butyl-, benzyl-, or octyl-groups as substituents) coordinated to different metal centers (Ni²⁺, Mn²⁺, or Co²⁺) as cations, and chloride anions were investigated. These water-soluble MILs were reacted with the bis[(trifluoromethyl)sulfonyl]imide anion during the extraction to generate a water-immiscible MIL capable of preconcentrating DNA. The feasibility of combining the extraction methodology with anion-exchange high-performance liquid chromatography with diode array detection (HPLC-DAD) or fluorescence spectroscopy was studied. The method with the Ni²⁺- and Co²⁺-based MILs was easily combined with fluorescence spectroscopy and provided a faster and more sensitive method than HPLC-DAD for the determination of DNA. In addition, the method was compared to conventional DLLME using analogous water-immiscible MILs. The developed in situ MIL-DLLME method required only 3 min for DNA extraction and yielded 1.1-1.5 times higher extraction efficiency (EFs) than the conventional MIL-DLLME method. The in situ MIL-DLLME method was also compared to the trihexyl(tetradecyl)phosphonium tris(hexafluorocetylaceto)nickelate(II) MIL, which has been used in previous DNA extraction studies. EFs of 42-99% were obtained using the new generation of MILs, whereas EFs of only 20-38% were achieved with the phosphonium MIL. This new class of MILs is simple and inexpensive to prepare. In addition, the MILs present operational advantages such as easier manipulation in comparison to hydrophobic MILs, which can have high viscosities. These MILs are a promising new class of DNA extraction solvents that can be manipulated using an external magnetic field. Graphical abstract Magnetic ionic liquids with metal-containing cations are applied in in situ dispersive liquid-liquid microextraction for the extraction of long and short double-stranded DNA.

Alternative Green Extraction Phases Applied to Microextraction Techniques for Organic Compound Determination

The use of green extraction phases has gained much attention in different fields of study, including in sample preparation for the determination of organic compounds by chromatography techniques. Green extraction phases are considered as an alternative to conventional phases due to several advantages such as non-toxicity, biodegradability, low cost and ease of preparation. In addition, the use of greener extraction phases reinforces the environmentally-friendly features of microextraction techniques. Thus, this work presents a review about new materials that have been used in extraction phases applied to liquid and sorbent-based microextractions of organic compounds in different matrices.

Organic Analysis of Environmental Samples Using Liquid Chromatography with Diode Array and Fluorescence Detectors: An Overview

This overview is focused to provide an useful guide of the families of organic pollutants that can be determined by liquid chromatography operating in reverse phase and ultraviolet/fluorescence detection. Eight families have been classified as the main groups to be considered: carbonyls, carboxyls, aromatics, phenols, phthalates, isocyanates, pesticides and emerging. The references have been selected based on analytical methods used in the environmental field, including both the well-established procedures and those more recently developed.

State-of-the-art on the technique of dispersive liquid-liquid microextraction

Dispersive liquid-liquid microextraction is a new sample pretreatment technology based on traditional liquid liquid extraction. In this paper, the application of low-toxicity extractants such as low-density extractants, auxiliary extractants, stripping agents and ionic liquids in this technology and the extraction modes such as solvent de-emulsification, suspension extractant curing, auxiliary extraction, back extraction, and ionic liquid-dispersion liquid microextraction, are summarized. In addition, the synergism of this technique with other sample preparation techniques, such as liquid-liquid extraction, solid-phase extraction, solid-phase microextraction, dispersive solid phase extraction, matrix solid-phase dispersion extraction, supercritical fluid extraction and ultrasound-assisted dispersive liquid-liquid microextraction is discussed.

Rational design of an ionic liquid dispersive liquid–liquid micro-extraction method for the detection of organophosphorus pesticides

In this study, a functionalized ionic liquid (IL), [MimCH₂COOCH₃][NTf₂] was rationally designed and explored as an extraction solvent in dispersive liquid–liquid microextraction (DLLME) combined with ultra-high performance liquid chromatography (UHPLC) for the sensitive determination of organophosphorus pesticides (OPs).

In situ formation of hydrophobic magnetic ionic liquids for dispersive liquid-liquid microextraction

A new class of magnetic ionic liquid (MIL) containing paramagnetic cations has been applied for in situ dispersive liquid-liquid microextraction in the determination of both polar and non-polar pollutants, including ultraviolet filters, polycyclic aromatic hydrocarbons, alkylphenols, a plasticizer and a preservative in aqueous samples. The MILs were based on cations containing Ni(II) metal centers coordinated with four N-alkylimidazole ligands and chloride anions. The MILs were capable of undergoing in situ metathesis reaction with the bis[(trifluoromethyl)sulfonyl]imide ([NTf₂^-]) anion during the microextraction procedure, generating a water-immiscible extraction solvent containing the preconcentrated analytes. The MIL was then isolated by magnetic separation, followed by direct analysis using reversed-phase high performance liquid chromatography with diode array detection. Among all of the studied MILs, those containing the N-butylimidazole and N-benzylimidazole ligands ([Ni(C₄IM)₄²⁺]2[Cl^-] and [Ni(BeIM)₄²⁺]2[Cl^-], respectively) exhibited the best extraction performance. The method under optimum conditions required 5 mL of sample at pH 3, 20 mg of [Ni(C₄IM)₄²⁺]2[Cl^-] or 30 mg of [Ni(BeIM)₄²⁺]2[Cl^-], 300 μL of acetone or acetonitrile as dispersive solvent (depending on the MIL), a 1:2 M ratio of MIL to [NTf₂^-], and 3 min of vortex. The developed method achieved higher extraction efficiency compared to the conventional MIL-dispersive liquid-liquid microextraction mode, with extraction efficiencies of 46.8-88.6% and 65.4-97.0% for the [Ni(C₄IM)₄²⁺]2[Cl^-] and the [Ni(BeIM)₄²⁺]2[Cl^-] MILs (at a spiked level of 81 μg L^-1), respectively, limits of detection down to 5.2 μg L^-1, and inter-day relative standard deviation lower than 16%.

Solvent Bar Micro-Extraction of Heavy Metals from Natural Water Samples Using 3-Hydroxy-2-Naphthoate-Based Ionic Liquids

Developments in the liquid micro-extraction of trace metals from aqueous phases have proven to be limited when extended from pure water to more complex and demanding matrices such as sea water or wastewater treatment effluents. To establish a system that works under such matrices, we successfully tested three task-specific ionic liquids, namely trihexyltetradecyl- phosphonium-, methyltrioctylphosphonium- and methyltrioctylammonium 3-hydroxy-2-naphthoate in two-phase solvent bar micro-extraction (SBME) experiments. We describe the influence of pH, organic additives, time, stirring rate and volume of ionic liquid for multi-elemental micro-extraction of Cu, Ag, Cd and Pb from various synthetic and natural aqueous feed solutions. Highest extraction for all metals was achieved at pH 8.0. Minimal leaching of the ionic liquids into the aqueous phase was demonstrated, with values < 30 mg L⁻¹ DOC in all cases. Sample salinities of up to 60 g L⁻¹ NaCl had a positive effect on the extraction of Cd, possibly due to an efficient extraction mechanism of the present chlorido complexes. In metal-spiked natural feed solutions, the selected SBME setups showed unchanged stability under all conditions tested. We could efficiently (≥85%) extract Cu and Ag from drinking water and achieved high efficacies for Ag and Cd from natural sea water and hypersaline water, respectively. The method presented here proves to be a useful tool for an efficient SBME of heavy metals from natural waters without the need to pretreat or modify the sample.

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.

Detection of Polycyclic Aromatic Hydrocarbons in Water Samples by Annular Platform-Supported Ionic Liquid-Based Headspace Liquid-Phase Microextraction

In this paper, a new method of annular platform-supported headspace liquid-phase microextraction (LPME) was designed using ionic liquid as an extraction solvent, wherein extraction stability and efficiency were improved by adding an annular platform inside the extraction bottle. The ionic liquid 1-silicyl-3-benzylimidazolehexafluorophosphate was first synthesized and proved to be an excellent extraction solvent. Coupled with liquid chromatography, the proposed method was employed to analysis of polycyclic aromatic hydrocarbons (PAHs) in water and optimized in aspects of extraction temperature, extraction solvent volume, extraction time, pH, stirring rate, and salt effect of solution. The results indicated that this method showed good linearity (R ² > 0.995) within 0.5 µg·L^-1 to 1000 µg·L^-1 for PAHs. The method was more suitable for extraction of volatile PAHs, with recoveries from 65.0% to 102% and quantification limits from 0.01 to 0.05 µg·L^-1. It has been successfully applied for detection of PAHs in seawater samples.

Hexafluoroisopropanol-based hydrophobic deep eutectic solvents for dispersive liquid-liquid microextraction of pyrethroids in tea beverages and fruit juices

A series of new hydrophobic deep eutectic solvents (DESs), which are liquid at room temperature and have high density (>1.4 g mL^-1), were synthesized using hexafluoroisopropanol (HFIP) as hydrogen-bond donor and l-carnitine/betaine as hydrogen-bond acceptor. Then these hydrophobic DESs were used as extraction solvents to establish dispersive liquid-liquid microextraction (DLLME) method for extraction of pyrethroids. The DES extraction phase was in the bottom after DLLME, being easy to be collected for analysis. After optimization by one-variable-at-a-time and response surface methodology, the enrichment factors of 265-360 were achieved for five pyrethroids. The proposed DLLME method coupled with HPLC has good performance: linear ranges of 0.25/0.5/1-100/200/400 ng/mL (r ≥ 0.9990), limits of detection of 0.06-0.17 ng mL^-1, relative recoveries of 85.1-109.4%, intra-day and inter-day RSDs below 7.5%. The novel DLLME method is simple, rapid, highly efficient and eco-friendly for extraction of pyrethroids in real tea beverages and fruit juices.

A green metal-organic framework to monitor water contaminants

The CIM-80 material (aluminum(iii)-mesaconate) has been synthetized in high yield through a novel green procedure involving water and urea as co-reactants. The CIM-80 material exhibits good thermal stability with a working range from RT to 350 °C with a small contraction upon desolvation. Moreover, this material is stable in water at different pH values (1-10) for at least one week, and shows a LC50 value higher than 2 mg mL-1. The new material has been tested in a microextraction methodology for the monitoring of up to 22 water pollutants while presenting little environmental impact: only 20 mg of CIM-80 and 500 μL of acetonitrile are needed per analysis. The analytical performance of the CIM-80 in the microextraction strategy is similar to or even better for several pollutants than that of MIL-53(Al). The average extraction efficiencies range from ∼20% for heavy polycyclic aromatic hydrocarbons to ∼70-100% for the lighter ones. In the case of the emerging contaminants, the average extraction efficiency can reach values up to 70% for triclosan and carbamazepine.

Enhanced magnetic ionic liquid-based dispersive liquid-liquid microextraction of triazines and sulfonamides through a one-pot, pH-modulated approach

In this study, an enhanced variant of magnetic ionic liquid (MIL)-based dispersive liquid-liquid microextraction is put forward. The procedure combines a water insoluble solid support and the [P₆₆₆₁₄⁺][Dy(III)(hfacac)₄^-] MIL, in a one-pot, pH-modulated procedure for microextraction of triazines (TZs) and sulfonamides (SAs). The solid supporting material was mixed with the MIL to overcome difficulties concerning the weighing of MIL and to control the uniform dispersion of the MIL, rendering the whole extraction procedure more reproducible. The pH-modulation during extraction step makes possible the one-pot extraction of SAs and TZs, from a single sample, in 15 min. Overall, the new analytical method developed enjoys the benefits of sensitivity (limits of quantification: 0.034-0.091 μg L^-1) and precision (relative standard deviation: 5.2-8.1%), while good recoveries (i.e., 89-101%) were achieved from lake water and effluent from a municipal wastewater treatment plant. Owing to all of the above, the new procedure can be used to determine the concentrations of SAs and TZs at levels below the maximum residue limits.

Simultaneous determination of Brilliant Green and Crystal Violet dyes in fish and water samples with dispersive liquid-liquid micro-extraction using ionic liquid followed by zero crossing first derivative spectrophotometric analysis method

In this study, dispersive liquid-liquid micro-extraction using ionic liquid (IL-DLLME) combined with zero crossing first derivative spectrophotometric method was applied to quantitative determination of triphenylmethane dyes in binary mixtures. The 1-methyl-3-octylimidazolium hexafluorophosphate [OMIM][PF₆] ionic liquid was used to extract Brilliant Green (BG) and Crystal Violet(CV) dyes from aqueous solutions. The amplitude of the zero crossing first derivative spectra at 670 nm and 532 nm were selected for the determination of BG and CV, respectively. Significant factors influencing the extraction of BG and CV such as sample pH, kind of extraction solvent, amount of extractant, extraction and centrifuging times and ionic strength were investigated. Under the optimal conditions, the calibration curves for the simultaneous determination of both dyes were found to be linear in the range of 10-500 μg L^-1 with detection limits (LODs) of 2.7 μg L^-1 and 1.4 μg L^-1 for BG and CV, respectively. The relative standard deviation (RSD%) for five replicate simultaneous determinations of BG and CV were 4.7% and 1.7%, respectively. Extraction efficiencies of the BG and CV dyes in the presence of interfering ions were also investigated. Sample preparation based on the quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction combined with the IL-DLLME method and zero crossing first derivative spectrophotometric detection was applied for the simultaneous analysis of BG and CV in fish and water samples with quantitative recoveries.

Recent Advances in Applications of Ionic Liquids in Miniaturized Microextraction Techniques

Green sample preparation is one of the most challenging aspects in green analytical chemistry. In this framework, miniaturized microextraction techniques have been developed and are widely performed due to their numerous positive features such as simplicity, limited need for organic solvents, instrumentation of low cost and short time of extraction. Also, ionic liquids (ILs) have unequivocally a “green” character, which they owe to their unique properties including the re-usage, the high reaction efficiency and selectivity in room temperature, the ability to dissolve both organic and inorganic compounds, and thermal stability. In the present review, the recent advances in the application of ionic liquids in miniaturized liquid and solid phase extraction techniques as extractants, intermediate solvents, mediators and desorption solvents are discussed, quoting the advantages and drawbacks of each individual technique. Some of the most important sample preparation techniques covered include solid-phase microextraction (SPME), dispersive liquid-liquid microextraction (DLLME), single-drop microextraction (SDME), stir bar sorptive extraction (SBSE), and stir cake sorptive extraction (SCSE).

Quantification of Meloxicam in Human Plasma Using Ionic Liquid-Based Ultrasound-Assisted In Situ Solvent Formation Microextraction Followed by High-Performance Liquid Chromatography

A robust extraction method against the variations of sample ionic strength viz. ionic liquid-based ultrasound-assisted in situ solvent formation microextraction (IL-UA-ISFME) was coupled for the first time with high-performance liquid chromatography-ultraviolet detection (HPLC-UV), and successfully used as a more sustainable approach for the determination of meloxicam (MEL) in human plasma. Herein, a hydrophobic IL (1-butyl-3-methylimidazolium hexafluorophosphate) was formed by adding a hydrophilic IL (1-butyl-3-methylimidazolium tetrafluoroborate) to aqueous sample solution containing an ion-exchange reagent (sodium hexafluorophosphate). The target analyte was transferred into the IL medium while the extraction solvent was completely dispersed into the sample using ultrasonic irradiation and then, the settled enriched phase was injected to HPLC. Firstly, main factors affecting the microextraction performance were evaluated and optimized. The linearity was in the range of 5-1,500 ng mL-1 with regression coefficient corresponding to 0.997. Limits of detection (LOD; signal-to-noise ratio (S/N) = 3) and quantification (LOQ, S/N = 10) were 1 and 5 ng mL-1, respectively. An acceptable recovery range of 82.1-93.6% and satisfactory intra-assay (3.6-4.8%, n = 6) and inter-assay (3.3-5.1%, n = 9) precision as well as remarkable sample clean up exhibited good efficiency of the method. The freeze-thaw stability study was performed for samples and standard solutions. To study the applicability of the proposed method, it was employed for the determination of MEL in human plasma after oral administration of the drug and some pharmacokinetic data were achieved. The technique proved to be accurate and reliable for the screening intentions.

Ionic Liquid-Based Liquid-Liquid Microextraction for Benzodiazepine Analysis in Postmortem Blood Samples

Sample preparation is rapidly improving to fulfill the need for faster and more environmentally friendly alternatives. In this respect, ionic liquid-based dispersive liquid-liquid microextraction (IL-DLLME) is an interesting technique. However, it has not yet been evaluated for the analysis of postmortem samples, which are frequently analyzed in forensic toxicology. This study investigates the applicability of IL-DLLME coupled to liquid chromatography-tandem mass spectrometry (LC-MS/MS), for the analysis of benzodiazepines in postmortem blood of 11 forensic cases. The method was compared with a validated solid-phase extraction (SPE) method. Bland-Altman analysis was performed on 24 benzodiazepine measurements. Both methods gave comparable results, except for flurazepam and temazepam (>55% difference). A feasible explanation is high postmortem matrix variability that was not considered during IL-DLLME validation experiments. Another issue could be the use of a single nondeuterated SPE internal standard. Overall, IL-DLLME has proven its usability for the analysis of postmortem blood.