Instability mechanisms of supported liquid membranes for copper (II) ion extraction

The instability of supported liquid membranes (SLMs) for use in copper (II) ion extraction was investigated in this paper. The degradation behavior of these SLMs was monitored in situ by electrochemical impedance spectroscopy (EIS). The electrical properties of a SLM cell can be described by an equivalent circuit, R_s(C_mR_m)Q. The model parameters, membrane resistance (R_m) and membrane capacitance (C_m) can be used to characterize the degradation behavior of SLMs. Experimental data for R_m and C_m indicated that the loss of membrane liquid (ML) during the mass transfer process consists of three stages. Results also suggest that emulsion formation was the dominant instability mechanism for these SLMs. The solubility and osmotic pressure were also shown to not be major factors contributing to the instability although both contributed to the loss of the liquid membrane. The pore size of the polymeric support increased during the first run but remained almost constant in subsequent runs.     

Extraction of lutetium(III) from aqueous solutions by employing a single fibre‐supported liquid membrane

Transport behaviour of Lu(III) across a polypropylene hollow fibre‐supported liquid membrane containing di(2‐ethylhexyl)phosphoric acid (DEHPA) in dihexyl ether as a carrier has been studied. The donor phase was LuCl₃ in the buffer solution consisting of 0.2 M sodium acetate at pH 2.5–5.0. A miniaturised system with a single hollow fibre has been operated in a batch mode. The concentration of Lu(III) was determined by indirect voltammetric method using Zn–EDTA complex. The effect of pH and volume of the donor phase, DEHPA concentration in the organic (liquid membrane) phase, the time of extraction and the content of the acceptor phase on the Lu(III) extraction and stripping behaviour was investigated. The results were discussed in terms of the pertraction and removal efficiency, the memory effect and the mean flux of Lu(III). The optimal conditions for the removal of ¹⁷⁷Lu(III) from labelled ¹⁷⁷Lu‐radiopharmaceuticals were discussed and identified. The removal efficiency of Lu(III) greater than 99% was achieved at pH of the donor phase between 3.5 and 5.0 using DEHPA concentration in the organic phase of 0.47 M and the ratio of the donor to the acceptor phase of 182.     

Supported liquid membranes in hollow fiber liquid-phase microextraction (LPME)--practical considerations in the three-phase mode

In this work, three-phase liquid-phase microextraction (LPME) based on a supported liquid membrane (SLM) sustained in the wall of a hollow fiber was investigated with special focus on optimization of the experimental procedures in terms of recovery and repeatability. Recovery data for doxepin, amitriptyline, clomipramine, and mianserin were in the range of 67.8-79.8%. Within-day repeatability data for the four basic drugs were in the range of 4.1-7.7%. No single factor was found to be responsible for these variations, and the variability was caused by several factors related to the LPME extractions as well as to the final HPLC determination. Although the volume of the SLM varied within 0.4-3.1% RSD depending on the preparation procedure, and the volume of the acceptor solution varied within 4.8% RSD, both recoveries and repeatability were found to be relative insensitive to these variations. Thus, the handling of microliters of liquid in LPME was not a very critical factor, and the preparation of the SLM was accomplished in several different ways with comparable performance. Reuse of hollow fibers was found to suffer from matrix effects due to built-up of analytes in the SLM, whereas washing of the hollow fibers in acetone was beneficial in terms of recovery, especially for the extraction of the most hydrophobic substances. Several of the organic solvents used in the literature as SLM suffered from poor long-term stability, but silicone oil AR 20 (polyphenylmethylsiloxane), 2-nitrophenyl octyl ether (NPOE), and dodecyl acetate (DDA) all extracted with unaltered performance even after 60 days of storage at room temperature.     

Tripodal lipophilic ionophores: synthesis, cation binding and transport through liquid membranes

New C₃-symmetric lipophilic tripodal ionophores, Et(CH₂OCH₂COR)₃; R=NMePh (1), R=NEtPh (2), R=piperidyl (3), have been prepared and their binding abilities for alkali and alkaline earth metal cations evaluated by extraction equilibrium and cation transport through bulk liquid membranes. Experiments show that these ionophores have considerable potential for transporting lithium, sodium and calcium ions relative to potassium and magnesium ions. The cation transport rates by ionophores 1 and 2 decrease in the order Li⁺>Na⁺>Ca²⁺>Ba²⁺>K⁺>Mg²⁺, and the selectivities of Li⁺/K⁺, Na⁺/K⁺ and Ca²⁺/Mg²⁺ are 6.47–7.24, 6.05–6.19 and 9.39–16.13, respectively. The extraction selectivity sequences of the ionophores 1 and 2 are in agreement with the descending order of the cation transport rate, and the complexation constants in chloroform phase were estimated.     

Supported liquid membrane extraction with single hollow fiber for the analysis of fluoroquinolones from environmental surface water samples

In this work, the simple analytical method for the determination of four fluoroquinolone antibiotics: ciprofloxacin, enrofloxacin, norfloxacin and danofloxacin, in environmental surface water samples is described. Sample pretreatment step was performed by the application of a technique based on supported liquid membrane extraction with the configuration of single hollow fiber (HF-SLM). The HPLC system with diode array detection was used for final analysis of studied analytes. Various parameters affecting the extraction efficiency during HF-SLM enrichment, such as type of membrane diluent, pH of donor (sample) and acceptor phases, as well as an enrichment time and salt content of sample were studied. Using the presented hollow-fiber extraction high recovery (70–80%) was achieved. It gave enrichment factor above 100. The detection limits in surface water samples, for the four target antibiotics, were at range 0.01–0.02 μg/l, when 10 ml samples were processed. The obtained results demonstrate the applicability of presented method for the selective extraction of fluoroquinolones in environmental water samples at ultratrace level. Errors, expressed as relative standard deviation (RSD) were below 8%, for all tested concentration levels.     

Coupled transport of Ag(I) ions through triethanolamine–cyclohexanone-based supported liquid membranes

Facilitated transport of silver(I) ions in acidic medium, across a supported liquid membrane (SLM) by using triethanolamine (TEA) as carrier, dissolved in cyclohexanone, has been investigated. The parameters studied are HNO₃ concentration variation in the feed, pH of the feed solution, carrier concentration in the membrane phase, silver(I) ions concentration in the feed phase and KCN concentration in the stripping phase. Increase in H⁺ concentration by increasing HNO₃ concentration from 0.5 to 1 M results into an increase in silver ions flux but a decrease in flux has been found beyond 1 M HNO₃ concentration in the feed, providing a maximum flux of 3.21 × 10⁻⁷ mol/m² s at 1 M HNO₃. Increase in TEA concentration inside the membrane enhances flux with its maximum value at 2.25 M TEA. Further increase in the concentration of TEA leads to a decreased rate of transport due to the increase in viscosity of membrane liquid. The optimum conditions for Ag(I) ions transport are 1 M HNO₃ (feed), 2.25 M TEA (membrane) and 1.5 M KCN in the stripping phase. It has been observed that Ag(I) flux across the membrane tends to increase with increase in Ag(I) ions concentration in the feed phase. Applying the studied conditions to silver plating waste solutions, Ag ions have been removed up to 99% in a time interval of 5 h.     

Potential‐driven peptide extractions across supported liquid membranes: Investigation of principal operational parameters

Fundamental experiments on electromembrane extraction were performed to increase the basic knowledge about the current and the mass transfer of target peptides and background electrolyte ions. Three peptides (angiotensin 2, bradykinin, and enkephalin) were extracted from 500 μL aqueous donor solution (1 mM HCl, positive electrode), through a 200 μm supported liquid membrane (SLM) of 1‐octanol/di‐isobutylketon/di‐(2‐ethylhexyl) phosphate (55:35:10 w/w/w) sustained in the pores of a porous hollow fiber, and into 25 μL aqueous acceptor solution (50 mM HCl, negative electrode) present inside the lumen of the fiber by the application of an electrical potential (50 V) and agitation (1050 rpm). Recoveries were typically in the range of 55–65% after 5 min of extraction and were principally determined by the chemical composition of the SLM and by the applied voltage. The electrical current in the system was measured during the extraction and was close to 350 μA. The current arose to some extent from mass transfer of the target peptides, but the major contribution was due to a background current from di‐(2‐ethylhexyl) phosphate in the SLM and from mass transfer of background electrolytes. Operation at relatively low background current was important to maintain a stable system.     

Extraction and preconcentration of manganese(II) from biological fluids (water, milk and blood serum) using supported liquid membrane and membrane probe methods

A supported liquid membrane (SLM) technique was investigated to extract and preconcentrate Mn(II) from water, milk and blood serum. Di-2-ethylhexyl phosphoric acid (DEHPA) with kerosene as diluent was used as a carrier in the membrane to transport Mn(II) from the donor side to acceptor side. The membrane was modified with tri-n-octylphosphine oxide (TOPO) to increase its polarity. Various parameters were investigated to optimise the extraction efficiency: pH of the donor and acceptor phase, dilution factor, donor flow rate. Scanning electron microscope images of the membranes revealed that some matrix compounds were deposited on the surface, thus limiting the extraction process. The optimum conditions found were: pH 3 in the donor phase, 0.2 M nitric acid in the acceptor phase, donor flow rate between 1.0 and 0.3 ml min⁻¹, 15% (w/v) DEPHA and 10% TOPO in kerosene as a carrier in membrane, and dilution factors of 20 times for blood serum and 30 times for milk. The extraction efficiencies were found to be low but constant and highly reproducible showing, strong dependence on sample matrix. The new SLM extraction probe was developed and optimised for Mn(II) extraction. Compared to traditional SLM configurations, this is the simplest configuration. The use of stirring allows the same sample to be extracted many times giving higher extraction efficiency and to minimise the sample size. Adsorptive stripping voltammetry (AdSV) was applied to measure Mn(II) concentration. The optimised method was used to determine the concentration of Mn(II) in water, milk and blood serum samples.     

Fundamental studies on the electrokinetic transfer of net cationic peptides across supported liquid membranes

By the application of an electrical potential difference (25 V), 37 different peptides were extracted from 500 μL aqueous sample (10 mM formic acid, positive electrode), through a supported liquid membrane (SLM) impregnated in the walls of a porous hollow fiber, and into 25 μL aqueous acceptor solution (100 mM formic acid, negative electrode) present inside the lumen of the fiber. Most of the peptides were obtained by tryptic digestion of cytochrome c and bovine serum albumin, which yielded complex samples for extraction. Three different SLMs were utilized to correlate the peptides extractability with the highly variable physical-chemical properties of the peptides. The first SLM (pure eugenol) provided an electromembrane extraction system for hydrophobic and intermediate peptides (hydrophilicity values below 0.2), where the extraction of peptides into the SLM was mainly based on solvent interactions. The second SLM (1-octanol/di-isobutylketone/di-(2-ethylhexyl) phosphate) extracted both hydrophobic and hydrophilic peptides (hydrophilicity values in the range from -2 to+1) successfully, and the transfer of peptides was principally based on ionic interactions with di-(2-ethylhexyl) phosphate. The third SLM (1-octanol/15-crown-5 ether) was selective for hydrophobic peptides (negative hydrophilicity values), and complexation of the peptides with the crown ether was important for the migration of peptides into the acceptor solution.     

Studies on phenol permeation through supported liquid membranes containing functionalized polyorganosiloxanes

In this study, the functionalized, linear, hydrophobic fluid organosiloxane polymers, namely, methylhydrosiloxane–dimethylsiloxane copolymers supported on a polypropylene microporous flat sheet membrane (Celgard 2502 and 2402) have been tested as supported liquid membranes (SLMs) for phenol recovery from aqueous phases into a 0.1 M NaOH phase. The functionalized polymers include, Me₃SiO[MeSi(OR)O]_x[Me₂SiO]_ySiMe₃ (containing x = 15–18, 25–35 and 50–55 mol% of R, where R is –(CH₂)_nNMe₂ (n = 3 or 4 or 6) or –(CH₂)₂OEt pendent organofunctional groups. The functionalities, R, tested were derived from the commercially available 3-dimethylamino-1-propanol and 2-ethoxyethanol as well as newly synthesized 4-dimethylamino-1-butanol and 6-dimethylamino-1-hexanol which have been made for the purpose of this study.

The study showed that phenol permeation expressed as permeate flux through the membranes increases with the larger number of carbon spacers in the alkyl chain of the aminoalcohol pendent, larger porosity of the polypropylene support films, higher mol% of the methylhydrosiloxane portion functionalized and faster flow rates of both the feed and the receiving phases. Phenol permeation was enhanced significantly when the mol% of the methylhydrosiloxane portion was 50–55 or 25–35 with 6-dimethylamino-1-hexanol functionality supported on Celgard 2502.     

Revision of the volumetric method for measurements of liquid–liquid equilibria in binary systems

A theoretical analysis of the accuracy of the volumetric method for the determination of liquid–liquid equilibrium was carried out. The results show that, under certain conditions, this method can be used to investigate systems showing relatively small mutual solubilities. Relations were derived to estimate standard deviations of the equilibrium compositions determined by the volumetric method.

In the experimental part of the work, an apparatus for measurements of mutual solubilities of liquids was constructed. A procedure that enabled us to determine precisely volumes of liquid phases was developed. This procedure and apparatus present the advantage that relatively small amounts of samples are required (approximately 2 × 20 ml). Theoretical conclusions concerning the applicability of the volumetric method were checked by measuring mutual solubilities at 303.15 K in systems methylcyclohexane + N,N-dimethylformamide, 1-butanol + water and dimethyl phthalate + water. Further, the method was used to measure systematically the liquid–liquid equilibrium in systems ethyl acetate + ethylene glycol and phenyl acetate + ethylene glycol at temperatures from 293 to 323 K. Data for these systems were acquired by means of other methods as well and a good agreement was observed on comparison.     

Separation of lignosulfonate from its aqueous solution using supported liquid membrane

This paper presents an experimental and theoretical study on facilitated transport of lignosulfonate (LS) through a flat sheet supported liquid membrane using trioctylamine (TOA) as carrier and dichloroethane as diluent. The studies were carried out with various support materials and operating conditions (viz. carrier concentration, strip phase concentration, salt concentration, etc.) and their effects on the transport of LS. The results were analyzed to identify a suitable combination of support and operating condition that would yield best performance of the supported liquid membrane (SLM) in terms of fast and efficient transport of LS. The stability of the SLM was assessed in terms of loss of liquid from the pores of membrane support. The SLM is found to be stable till 10 h. Co-transport mechanism has been adopted in this work by using NaOH as the strip phase. It was observed that extraction of LS is increased with increase in concentration of NaOH up to a limiting value of 0.5 M NaOH. Difference of salt concentration between feed and strip phase considerably affect the separation process. The diffusional resistances of organic membrane (Δorg) and aqueous solution (Δaq) calculated from the permeation model, which is again a combination of three unique mechanisms viz., diffusion through a feed aqueous layer, a fast interfacial chemical reaction, and diffusion of carrier–complex through the organic membrane, are found to be 609.9 and 176.6 s cm⁻¹, respectively. The values of the diffusion coefficient in the membrane (D_org) and in the bulk organic phase (D_complex) are 1.67×10⁻⁹ and 6.68 × 10⁻⁸ m²s⁻¹, respectively. The extraction of LS is about 90%. Nearly 43% of LS can be recovered at optimum condition.     

Supported liquid membranes for the determination of vanillin in food samples with amperometric detection

A supported liquid membrane system has been developed for the extraction of vanillin from food samples. A porous PTFE membrane is impregnated with an organic solvent, which forms a barrier between two aqueous phases. The analyte is extracted from a donor phase into the hydrophobic membrane and then back extracted into a second aqueous solution, the acceptor. The determination (100–1400 μg ml⁻¹ vanillin) was performed using a PVC-graphite composite electrode versus Ag/AgCl/3MKCl at +0.850 V placed in a wall-jet flow cell as amperometric detector. The solid sample is directly placed in the membrane unit without any treatment, and the analyte was extracted from the sample, passes through the membrane and conduced to the flow cell by the acceptor stream. The limit of detection (3σ) was 44 μg ml⁻¹. The method was applied to the determination of vanillin (9–606 μg g⁻¹) in food samples.     

Evaluation of a calix[4]-bis-crown-6 ionophore-based supported liquid membrane system for selective Cs transport from acidic solutions

Facilitated transport of Cs(I) from aqueous nitrate feed solutions to a receiver solution containing distilled water through a supported liquid membrane (SLM) containing calix[4]-bis-2,3-naphtho-crown-6 (CNC) in 0.45 μm PTFE (polytetrafluoroethylene) membranes was investigated. The carrier solution usually consisted of CNC dissolved in a mixture of 80% 2-nitrophenyl octyl ether and 20% n-dodecane. The transport rates were found to be influenced by the mobile carrier concentration, cesium concentration as well as the feed acidity. The extracted species conformed to a stoichiometry of 1:1 metal to ligand ratio suggesting the extraction of an organophilic mono-Cs-crown complex. Fission products obtained from an irradiated natural uranium target were found to be poorly transported while Cs-137 got significantly transported suggesting the possible application of the separation method for the removal of bulk Cs-137 from radioactive waste solutions. Durability/chemical stability of the membrane was remarkably good when tested over 20 days of continuous operation.     

Pore size distribution of ceramic UF membranes by liquid–liquid displacement porosimetry

Commercial ceramic tubular membranes made by Tami^® have been characterized by several techniques. Their pore size distributions (PSD) have been obtained by liquid–liquid displacement porosimetry (LLDP).

Computerized image analysis (CIA) of SEM pictures has been used to get information on the width of the active layer of the studied membranes. These values of thickness have helped to evaluate the porosity of the membranes and to get representative radii from measurements of the permeability to several gases and liquids. A fully automated porosimeter designed by us has been used in the determination of pore size distributions. Results show a good accuracy and reproducibility of LLDP measurements.

Binary and ternary liquid mixtures have been used to wet and penetrate into the membrane pores when performing LLDP leading to quite similar results when an effective surface tension is assigned for the ternary mixture. This procedure can be used to calibrate the technique to be extended to thick ultrafiltration and even to nanofiltration membranes.     

苯酚在N-503/煤油支撑液膜体系中的传输分离

研究了以多孔聚丙烯膜为支撑体,N,N′-二(1-甲基庚基)乙酰胺(N-503)为膜流动载体的苯酚支撑液膜传输行为;用液-液萃取法测定了N-503/煤油体系中苯酚萃合物组成为1∶1,及在相应的条件下萃取常数Ke′x为53.7;考察了料液相的pH值、载体浓度、实验温度、起始浓度以及解析相NaOH的浓度对苯酚传输的影响,并对该体系分离、传输苯酚的最佳条件进行了讨论;从界面化学和扩散传质角度提出了苯酚的传输动力学方程,采用直线斜率法对苯酚在N-503/煤油支撑液膜体系中的扩散层厚度和膜内扩散系数进行了测定,取得满意结果。     

Multivariate optimization of a liquid-liquid extraction of the EPA-PAHs from natural contaminated waters prior to determination by liquid chromatography with fluorescence detection

This paper reports the multivariate optimization of a liquid–liquid extraction procedure for the determination of 15 EPA-polycyclic aromatic hydrocarbons (PAHs) by high-performance liquid chromatography with fluorescence detection. A Doehlert design was used to find optimum conditions for the procedure through Response Surface Methodology. Three variables (total volume of hexane, number of extraction steps and duration of such steps) were elected as factors in the optimization study. A principal component analysis (PCA) was run with optimized data, resulting in four groups of PAHs, ordered according to their molecular weight. Final working conditions were established in order to achieve a more robust methodology in relation to all fifteen PAHs under study. Best results could be observed when 77 mL of hexane were divided in four consecutive extraction steps with 18 min each. These experimental conditions were applied in the analysis of a spiked river water sample, and the recoveries varied between 80.9 and 106%, with an average value of 97.1 ± 6.8%. The application of the methodology to river water showed that the method has a good average precision for the studied PAHs.     

Pressurized liquid extraction of organophosphate triesters from sediment samples using aqueous solutions

A novel procedure for the extraction of seven organophosphate triesters (OPs), used as flame retardants and plasticizers, from sediment samples has been developed. It is based on the pressurized liquid extraction of the analytes with aqueous solutions, combined with a further concentration step using solid-phase extraction (SPE) and followed by gas chromatography coupled to mass spectrometry (GC-MS) determination. The effects of different variables on the yield and selectivity of the sample preparation process are systematically evaluated. The optimal responses were observed extracting 2 g of sediment with a water:acetonitrile (75:25) solution at 90 °C and 1500 psi for 5 min. The obtained extract was made up to 200 mL with ultrapure water and passed through an OASIS HLB, 60 mg cartridge. Analytes were recovered with 2 mL of ethyl acetate and this extract concentrated to a lower volume, ca. 0.2 mL. Recoveries of the proposed extraction method ranged from 77 to 111%, with relative standard deviations below 10%, for spiked river and marine sediment samples with total carbon contents (TC) up to 4.0%. The limits of quantification (LOQs) of the method varied between 0.5 and 5 ng g⁻¹. Analysis of non-spiked sediment samples revealed the presence of low levels for some of the investigated species, with the highest concentration (47 ng g⁻¹) corresponding to tris(2-chloroethyl) phosphate (TCEP).     

Supported imidazolium ionic liquid phases: A new material for solid-phase extraction

This study reports a material that is based on the concept of ionic liquid analogue: a slightly crosslinked polymer-supported imidazolium trifluoroacetate salt (IL-CF₃COO⁻) that favorably combines the properties of ionic liquids (ILs) and the advantages of a solid support.The ionic liquid-supported material was evaluated for the first time as a solid-phase extraction (SPE) sorbent for selectively and quantitatively extracting pharmaceuticals from aqueous samples.The novel IL-CF₃COO⁻ was evaluated under reversed-phase (RP), weak anion exchange (WAX), strong anion exchange (SAX) and strong cation exchange (SCX) SPE procedures, and we found that SAX conditions are the most suitable for investigating the behaviour of the IL-CF₃COO⁻ material. Under SAX conditions, the IL-CF₃COO⁻ material was capable of selectively and quantitatively extracting a group of acidic compounds from aqueous samples, while washing basic analytes that were also present in the sample.The SPE method using IL-CF₃COO⁻ material was used to analyse 1000 ml of different aqueous samples (ultrapure, tap and river) with complete recovery of the acidic compounds studied. Moreover, the method provided clean chromatogram and high recoveries when percolating complex real samples, such as 1000 ml of river water and 250 ml of effluent wastewater from a sewage treatment plant spiked at low levels with the analytes studied.     

Impedometric monitoring of the behavior of the supported liquid membrane in electromembrane extraction systems: An insight into the origin of optimized experimental parameters

Electromembrane extraction (EME) was carried out using a novel instrumentation capable of impedometric monitoring of the system during the extraction. This instrumentation involves a classical two-electrode assembly fed by two time-resolved potential functions, the first for the extraction of analyte and the second for obtaining the impedance information. The impedometric analysis of the system was achieved by Laplace transformation of the current recorded during the extraction. It has been shown that the obtained impedance information can be converted to very useful knowledge about time dependence of double layer capacitance, kinetics of analyte depletion, total permeability of the SLM and the effect of experimental parameters on system behavior. It has also been shown that the impedance analysis is a powerful tool for the estimation of optimum experimental parameters without determination of analyte in the acceptor phase.