Circulation microchannel for liquid–liquid microextraction

A new method has been developed for liquid–liquid microextraction utilizing a circulation microchannel. A glass microchemical chip having a circular shallow microchannel in contact with a surrounding deeper microchannel was fabricated by a two-step photolithographic wet-etching technique. Surface modification reagent was selectively introduced to the shallow channel by utilizing capillary force, and the surface of the shallow channel was selectively made hydrophobic. With the aid of the hydrophobic/hydrophilic surface patterning, it was possible to keep organic solvent in the circular channel while the aqueous sample solution was continuously flowing in the deep channel. As a result, concentration extraction from sample solution to stationary extractant with a nanoliter scale volume became possible. Concentration extraction has been difficult in a multiphase continuous flow. Function of the newly developed microextraction system was verified with methyl red as a test sample, and concentration extraction to reach equilibrium was successfully carried out. A novel surface modification method utilizing frozen liquid as a masking material was also developed as a reverse process to make the shallow channel hydrophilic and the deep channel hydrophobic. Visualization of circulation motion inside the circular shallow channel induced by flow in the deep channel was observed with a particle tracing method.     

Preconcentration technique for nonylphenol using cellulose cotton with homogenous liquid–liquid extraction for liquid chromatographic analysis

A powerful preconcentration method for nonylphenol (NP) has been developed for liquid-chromatography by combining the use of cellulose cotton (solid-phase extraction) with homogeneous liquid–liquid extraction. A 100 ml of sample solution was preconcentrated using cotton, and the eluate obtained (acetonitrile; 5 ml) was further preconcentrated to 50 l within 10 min using a homogeneous liquid–liquid extraction method (volume ratio, 2,000-fold; 100 ml 50 l). The sample concentration increases from preconcentration was 1,599-fold, and NP was extracted into the sedimented phase at 80%. The proposed method was applied to high performance liquid chromatography with fluorescence detection (FL/HPLC); the lowest determination limit obtained was 1.0×10^–9 mol l^–1.     

Microfluidic lab-on-chip advances for liquid–liquid extraction process studies

The ever-increasing complexity of industrial product recycling calls for more efficient purification processes such as liquid–liquid (L/L) extraction. Because of the high complexity of L/L extraction, optimizing a large-scale extraction is both time and resource consuming and can only be justified to solve high volume and value purification problems. It is therefore difficult to apply to small scale and highly variable waste material influx. We believe using a fully automated and integrated microfluidic approach will enable fast and cost-effective studies of L/L extraction processes. This review presents an overview of L/L metal extraction performed using microfluidics platforms. We first give an overview of the extraction methods. We then review the most relevant characterization methods integrated with such platforms.     

Microfluidic chip for electrochemically-modulated liquid∣liquid extraction of ions

A microfluidic device with integrated electrodes for the electrochemically-modulated extraction of ions across immiscible aqueous–organic liquid–liquid interfaces is presented. Using a Y-shaped microfluidic channel with in situ electrodes and co-flowing aqueous and organic immiscible electrolyte solutions, the manipulation of the applied interfacial potential enabled the extraction of ions from the aqueous phase into the organic phase. Data for the extraction of tetraethylammonium cations from aqueous electrolyte into 1,2-dichloroethane electrolyte are presented. The device demonstrates the benefits of combination of microfluidics and liquid–liquid electrochemistry.     

Dispersive liquid–liquid microextraction coupled to liquid chromatography for thiamine determination in foods

A miniaturized dispersive liquid–liquid microextraction (DLLME) procedure coupled to liquid chromatography (LC) with fluorimetric detection was evaluated for the preconcentration and determination of thiamine (vitamin B₁). Derivatization was carried out by chemical oxidation of thiamine with 5 × 10⁻⁵ M ferricyanide at pH 13 to form fluorescent thiochrome. For DLLME, 0.5 mL of acetonitrile (dispersing solvent) containing 90 μL of tetrachloroethane (extraction solvent) was rapidly injected into 10 mL of sample solution containing the derivatized thiochrome and 24% (w/v) sodium chloride, thereby forming a cloudy solution. Phase separation was carried out by centrifugation, and a volume of 20 μL of the sedimented phase was submitted to LC. The mobile phase was a mixture of a 90% (v/v) 10 mM KH₂PO₄ (pH 7) solution and 10% (v/v) acetonitrile at 1 mL min⁻¹. An amide-based stationary phase involving a ligand with amide groups and the endcapping of trimethylsilyl was used. Specificity, linearity, precision, recovery, and sensitivity were satisfactory. Calibration graph was carried out by the standard additions method and was linear between 1 and 10 ng mL⁻¹. The detection limit was 0.09 ng mL⁻¹. The selectivity of the method was judged from the absence of interfering peaks at the thiamine elution time for blank chromatograms of unspiked samples. A relative standard deviation of 3.2% was obtained for a standard solution containing thiamine at 5 ng mL⁻¹. The esters thiamine monophosphate and thiamine pyrophosphate can also be determined by submitting the sample to successive acid and enzymatic treatments. The method was applied to the determination of thiamine in different foods such as beer, brewer’s yeast, honey, and baby foods including infant formulas, fermented milk, cereals, and purees. For the analysis of solid samples, a previous extraction step was applied based on an acid hydrolysis with trichloroacetic acid. The reliability of the procedure was checked by analyzing a certified reference material, pig’s liver (CRM 487). The value obtained was 8.76 ± 0.2 μg g⁻¹ thiamine, which is in excellent agreement with the certified value, 8.6 ± 1.1 μg g⁻¹.     

Ionic liquid based dispersive liquid–liquid microextraction for the extraction of pesticides from bananas

This paper describes a dispersive liquid–liquid microextraction (DLLME) procedure using room temperature ionic liquids (RTILs) coupled to high-performance liquid chromatography with diode array detection capable of quantifying trace amounts of eight pesticides (i.e. thiophanate-methyl, carbofuran, carbaryl, tebuconazole, iprodione, oxyfluorfen, hexythiazox and fenazaquin) in bananas. Fruit samples were first homogenized and extracted (1 g) with acetonitrile and after suitable evaporation and reconstitution of the extract in 10 mL of water, a DLLME procedure using 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) as extraction solvent was used. Experimental conditions affecting the DLLME procedure (sample pH, sodium chloride percentage, ionic liquid amount and volume of disperser solvent) were optimized by means of an experimental design. In order to determine the presence of a matrix effect, calibration curves for standards and fortified banana extracts (matrix matched calibration) were studied. Mean recovery values of the extraction of the pesticides from banana samples were in the range of 69–97% (except for thiophanate-methyl and carbofuran, which were 53–63%) with a relative standard deviation lower than 8.7% in all cases. Limits of detection achieved (0.320–4.66 μg/kg) were below the harmonized maximum residue limits established by the European Union (EU). The proposed method, was also applied to the analysis of this group of pesticides in nine banana samples taken from the local markets of the Canary Islands (Spain). To the best of our knowledge, this is the first application of RTILs as extraction solvents for DLLME of pesticides from samples different than water.     

Automated apparatus for the rapid determination of liquid–liquid and solid–liquid phase transitions

An automated apparatus developed for the determination of liquid–liquid and solid–liquid equilibrium temperatures with a resolution of 1 mK and a traceable accuracy of 0.01 K is described. The amount of light transmitted through six sample cells placed in a computer controlled thermostat is recorded at heating or cooling rates from 0.075 to 15 K h⁻¹. The construction does not require expensive optic equipment like lasers, glass fibre optics or photomultipliers, but is based on light emitting diodes (LED) as light sources and light dependent resistors (LDR) or photodiodes as detectors. As shown by the discussed examples, the instrument has a wide range of possible applications from the investigation of simple one-component and binary systems to the study of the complicated phase behavior of surfactant solutions.     

A simple novel configuration for in-vial microporous membrane liquid–liquid extraction

A novel arrangement for microporous membrane liquid–liquid extraction from the aqueous donor phase to the organic acceptor phase within a micro-vial, which is compatible with the chromatograph autosampler is presented. The device consisted of a stoppered glass micro-vial containing the organic solvent where the septum of the screw stopper was replaced by a sized piece of membrane which is hermetically assembled to the volumetric flask containing the aqueous donor solution. The placement of the membrane in alternative contact with the solutions was achieved by orbital agitation. As a preliminary study, 2-ethylhexyl 4-(dimethylamino)benzoate has been determined (limit of quantification 0.11 μg L⁻¹, precision 7.4%). The small quantity of organic solvent used, the achieved sample cleanup, and the minimal handling and risk of cross-contamination are significant operational advantages.     

Dispersive liquid–liquid–liquid microextraction combined with liquid chromatography for the determination of chlorophenoxy acid herbicides in aqueous samples

A novel sample preparation method “Dispersive liquid–liquid–liquid microextraction” (DLLLME) was developed in this study. DLLLME was combined with liquid chromatography system to determine chlorophenoxy acid herbicide in aqueous samples. DLLLME is a rapid and environmentally friendly sample pretreatment method. In this study, 25 μL of 1,1,2,2-tetrachloroethane was added to the sample solution and the targeted analytes were extracted from the donor phase by manually shaking for 90 s. The organic phase was separated from the donor phase by centrifugation and was transferred into an insert. Acceptor phase was added to this insert. The analytes were then back-extracted into the acceptor phase by mixing the organic and acceptor phases by pumping those two solutions with a syringe plunger. After centrifugation, the organic phase was settled and removed with a microsyringe. The acceptor phase was injected into the UPLC system by auto sampler. Fine droplets were formed by shaking and pumping with the syringe plunger in DLLLME. The large interfacial area provided good extraction efficiency and shortened the extraction time needed. Conventional LLLME requires an extraction time of 40–60 min; an extraction time of approximately 2 min is sufficient with DLLLME. The DLLLME technique shows good linearity (r² ≥ 0.999), good repeatability (RSD: 4.0–12.2% for tap water; 5.7–8.5% for river water) and high sensitivity (LODs: 0.10–0.60 μg/L for tap water; 0.11–0.95 μg/L for river water).     

New calculation method for asymmetric closed-loop liquid—liquid equilibria by lattice decoration

A new calculation method for the binary closed-loop coexistence curves of liquid—liquid equilibria has been developed in terms of lattice decoration and the UNIQUAC equation. Two-step renormalization was performed to evaluate the effective interaction energies of sites and the activities of binary mixtures in the decorated lattice consisting of primary and secondary cells. In application, the model reproduced fairly well temperature-composition diagrams which are asymmetric and closed in a loop or have lower consolute points.     

Dispersive liquid–liquid microextraction based on ionic liquid in combination with high-performance liquid chromatography for the determination of bisphenol A in water

A method termed dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography-variable wavelength detection (HPLC-VWD) was developed. DLLME-HPLC-VWD is a method for determination of bisphenol A (BPA) in water samples. In this microextraction method, several parameters such as extraction solvent volume, sample volume, disperser solvent, ionic strength, pH, and disperser volume were optimised with the aid of interactive orthogonal array and a mixed level experiment design. First, an orthogonal array design was used to screen the significant variables for the optimisation. Second, the significant factors were optimised by using a mixed level experiment. Under the optimised extraction conditions (extraction solvent: ionic liquid [C₆MIM][PF₆], 60 µL; dispersive solvent: methanol, 0.4 mL; and pH = 4.0), the performance of the established method was evaluated. The response linearity of the method was observed in a range of 0.002–1.0 mg L^?1 (three orders of magnitude) with correlation coefficient (R ²) of 0.9999. The repeatability of this method was 4.2–5.3% for three different BPA levels and the enrichment factors were above 180. The extraction recovery was about 50% for the three different concentrations with 3.4–6.4% of RSD. Limit of detection of the method was 0.40 µg L^?1 at a signal-to-noise ratio of 3. In addition, the relative recovery of sample of Songhua River, tap water and barrel-drain water at different spiked concentration levels was ranged 95.8–103.0%, 92.6–98.6% and 87.2–95.3%, respectively. Compared with other extraction technologies, there have been the following advantages of quick, easy operation, and time-saving for the present method.     

Membrane activity of ionisable drugs – a task for liquid–liquid electrochemistry?

Structurally related aminoacridine therapeutics (aminacrine, tacrine, velnacrine and proflavine) were studied electrochemically at the interface between two immiscible electrolyte solutions. To assess both their neutral and ionic partition coefficients, cyclic voltammetry was used to obtain the transfer potential as a function of the aqueous phase pH. Subsequently, in order to create a simple model of a biological membrane, a lipid monolayer was deposited at the liquid–liquid interface using the Langmuir–Blodgett technique. Electrochemical impedance spectroscopy was employed to study the interactions between the drug ions and the biomimetic phospholipid monolayer. Using a model incorporating a charge transfer mechanism coupled with potential dependent adsorption steps, the membrane activity of the studied drug ions could be estimated. The results indicate liquid–liquid electrochemistry to be a versatile tool for detecting differences in membrane activity even between structurally very similar drugs.     

Sequential injection ionic liquid dispersive liquid–liquid microextraction for thallium preconcentration and determination with flame atomic absorption spectrometry

A novel, automatic on-line sequential injection dispersive liquid-liquid microextraction (SI-DLLME) method, based on 1-hexyl-3-methylimidazolium hexafluorophosphate ([Hmim][PF(6)]) ionic liquid as an extractant solvent was developed and demonstrated for trace thallium determination by flame atomic absorption spectrometry. The ionic liquid was on-line fully dispersed into the aqueous solution in a continuous flow format while the TlBr(4)(-) complex was easily migrated into the fine droplets of the extractant due to the huge contact area of them with the aqueous phase. Furthermore, the extractant was simply retained onto the surface of polyurethane foam packed into a microcolumn. No specific conditions like low temperature are required for extractant isolation. All analytical parameters of the proposed method were investigated and optimized. For 15 mL of sample solution, an enhancement factor of 290, a detection limit of 0.86 μg L(-1) and a precision (RSD) of 2.7% at 20.0 μg L(-1) Tl(I) concentration level, was obtained. The developed method was evaluated by analyzing certified reference materials while good recoveries from environmental and biological samples proved that present method was competitive in practical applications.     

Dispersive liquid–liquid microextraction followed by high-performance liquid chromatography for the determination of three carbamate pesticides in water samples

A simple, rapid and efficient method, dispersive liquid–liquid microextraction (DLLME) in conjunction with high-performance liquid chromatography (HPLC), has been developed for the determination of three carbamate pesticides (methomyl, carbofuran and carbaryl) in water samples. In this extraction process, a mixture of 35 µL chlorobenzene (extraction solvent) and 1.0 mL acetonitrile (disperser solvent) was rapidly injected into the 5.0 mL aqueous sample containing the analytes. After centrifuging (5 min at 4000 rpm), the fine droplets of chlorobenzene were sedimented in the bottom of the conical test tube. Sedimented phase (20 µL) was injected into the HPLC for analysis. Some important parameters, such as kind and volume of extraction and disperser solvent, extraction time and salt addition were investigated and optimised. Under the optimum extraction condition, the enrichment factors and extraction recoveries ranged from 148% to 189% and 74.2% to 94.4%, respectively. The methods yielded a linear range in the concentration from 1 to 1000 µg L^?1 for carbofuran and carbaryl, 5 to 1000 µg L^?1 for methomyl, and the limits of detection were 0.5, 0.9 and 0.1 µg L^?1, respectively. The relative standard deviations (RSD) for the extraction of 500 µg L^?1 carbamate pesticides were in the range of 1.8–4.6% (n = 6). This method could be successfully applied for the determination of carbamate pesticides in tap water, river water and rain water.     

On-column liquid–liquid–liquid microextraction coupled with base stacking as a dual preconcentration method for capillary zone electrophoresis

A simple and efficient dual preconcentration method of on-column liquid–liquid–liquid microextraction (LLLME) coupled with base stacking was developed for capillary zone electrophoresis (CZE) in this paper. Four N-methyl carbamates were used as target compounds to evaluate the enrichment means. The carbamates in sample solutions (donor phase) were extracted into a dodecanol phase immobilized on a porous hollow fiber, hydrolyzed and back extracted into 0.20 μL running buffer (acceptor phase) of 30 mmol/L methylamine hydrochloride (pH 11.6) containing 0.5 mmol/L tetradecyltrimethylammonium bromide inside the hollow fiber, stacked further with 0.5 mol/L NaOH injected at −10 kV for 60 s, and separated by CZE. Analytical parameters affecting the LLLME, base stacking and CZE were investigated, including sample solution volume, pH and temperature, extraction time, stirring rate, buffer component, buffer pH, NaOH concentration, stacking time, etc. The enrichment factors of the carbamates were higher than 1100. The relative standard deviation (RSD) of peak height and limits of detection (LODs) were 4.5–5.5% (n = 6) and 2–4 ng/mL (S/N = 3) for standard solutions, respectively. The proposed method was applied to the analysis of vegetable and fruit samples with the RSD less than 6.0% (n = 3) and LODs of 6–10 ng/g (S/N = 3). The calibration solutions were prepared by diluting the stock solutions with blank sample solutions, and the calibration concentrations ranged from 0.012 to 1.0 μg/mL (r > 0.9951). The analytical results demonstrated that the LLLME coupled with base stacking was a simple, convenient and reliable on-column sample pretreatment method for the analysis of anionic analytes in CZE.     

Optimization of parameters for the alcoholic-assisted dispersive liquid–liquid microextraction of estrogens in water

Extraction and determination of estrogens in water samples were performed using alcoholic-assisted dispersive liquid–liquid microextraction (AA-DLLME) and high-performance liquid chromatography (UV/Vis detection). A Plackett–Burman design and a central composite design were applied to evaluate the AA-DLLME procedure. The effect of six parameters on extraction efficiency was investigated. The factors studied were volume of extraction and dispersive solvents, extraction time, pH, amount of salt and agitation rate. According to Plackett–Burman design results, the effective parameters were volume of extraction solvent and pH. Next, a central composite design was applied to obtain optimal condition. The optimized conditions were obtained at 220 μL 1-octanol as extraction solvent, 700 μL ethanol as dispersive solvent, pH 6 and 200 μL sample volume. Linearity was observed in the range of 1–500 μg L^?1 for E2 and 0.1–100 μg L^?1 for E1. Limits of detection were 0.1 μg L^?1 for E2 and 0.01 μg L^?1 for E1. The enrichment factors and extraction recoveries were 42.2, 46.4 and 80.4, 86.7, respectively. The relative standard deviations for determination of estrogens in water were in the range of 3.9–7.2 % (n = 3). The developed method was successfully applied for the determination of estrogens in environmental water samples.     

Vapor—liquid and vapor—liquid—liquid phase equilibria for binary and ternary systems for nitrogen,ethane and methanol: Experiment and data reduction

Zeck, S. and Knapp, H., 1986. Vapor-liquid and vapor-liquid-liquid phase equilibria for binary and ternary systems of nitrogen, ethane and methanol; experiment and data reduction. Fluid Phase Equilibria, 25: 302–322.VLE and VLLE are investigated for three binary and one ternary system containing N₂, C₂H₆ and CH₃OH in a high-pressure phase equilibrium apparatus with vapor recirculation at temperatures 240 < T < 298 K and pressures 4 < p < 75 bar. Two liquid phases are observed in the systems C₂H₆CH₃OH and N₂CH₃OH. Experimental results are reported and compared with available correlations.     

Ultrasound-assisted dispersive liquid–liquid microextraction for the determination of six pyrethroids in river water

A simple ultrasound-assisted dispersive liquid–liquid microextraction method combined with liquid chromatography was developed for the preconcentration and determination of six pyrethroids in river water samples. The procedure was based on a ternary solvent system to formatting tiny droplets of extractant in sample solution by dissolving appropriate amounts of water-immiscible extractant (tetrachloromethane) in watermiscible dispersive solvent (acetone). Various parameters that affected the extraction efficiency (such as type and volume of extraction and dispersive solvent, extraction time, ultrasonic time, and centrifuging time) were evaluated. Under the optimum condition, good linearity was obtained in a range of 0.00059–1.52 mg L⁻¹ for all analytes with the correlation coefficient (r²) > 0.999. Intra-assay and inter-assay precision evaluated as the relative standard deviation (RSD) were less than 3.4 and 8.9%. The recoveries of six pyrethroids at three spiked levels were in the range of 86.2–109.3% with RSD of less than 8.7%. The enrichment factors for the six pyrethroids were ranged from 767 to 1033 folds.     

Ultrasound-enhanced surfactant-assisted dispersive liquid–liquid microextraction and high-performance liquid chromatography for determination of ketoconazole and econazole nitrate in human blood

A simple and efficient method, based on ultrasound-enhanced surfactant-assisted dispersive liquid–liquid microextraction (UESA-DLLME) followed by high-performance liquid chromatography (HPLC) has been developed for extraction and determination of ketoconazole and econazole nitrate in human blood samples. In this method, a common cationic surfactant, cetyltrimethylammonium bromide (CTAB), was used as dispersant. Chloroform (40 μL) as extraction solvent was added rapidly to 5 mL blood containing 0.068 mg mL⁻¹ CTAB. The mixture was then sonicated for 2 min to disperse the organic chloroform phase. After the extraction procedure, the mixture was centrifuged to sediment the organic chloroform phase, which was collected for HPLC analysis. Several conditions, including type and volume of extraction solvent, type and concentration of the surfactant, ultrasound time, extraction temperature, pH, and ionic strength were studied and optimized. Under the optimum conditions, linear calibration curves were obtained in the ranges 4–5000 μg L⁻¹ for ketoconazole and 8–5000 μg L⁻¹ for econazole nitrate, with linear correlation coefficients for both >0.99. The limits of detection (LODs, S/N = 3) and enrichment factors (EFs) were 1.1 and 2.3 μg L⁻¹, and 129 and 140 for ketoconazole and econazole nitrate, respectively. Reproducibility and recovery were good. The method was successfully applied to the determination of ketoconazole and econazole nitrate in human blood samples.