Automated sample preparation using supported liquid membranes for liquid chromatographic determination of sulfonylurea herbicides

Summary Sample preparation for determination of sulfonylurea herbicides in aqueous samples is investigated. The technique studied utilizes extraction and back extraction in an automated flow system and is coupled on-line to a liquid chromatographic system. The extraction unit consists of an immobilized liquid membrane, separating two aqueous phases. From the acidified donor phase the analytes are extracted into the organic solvent of the membrane. After traversing the membrane they are back extracted into an alkaline/neutral aqueous acceptor phase. They are trapped in the acceptor by dissociation, making them insoluble in the membrane.Studies of the sample preparation system concern factors like channel length of separators, distribution coefficients of analytes and use of a precolumn instead of loop for chromatographic injections. Effects of the internal diameter of the analytical column as well as the detection of the sulfonylurcas are investigated.     

Positioning lipid membrane domains in giant vesicles by micro-organization of aqueous cytoplasm mimic

We report localization of lipid membrane microdomains to specific "poles" of asymmetric giant vesicles (GVs) in response to local internal composition. Interior aqueous microdomains were generated in a simple model cytoplasm composed of a poly(ethyleneglycol) (PEG)/dextran aqueous two-phase system (ATPS) encapsulated in the vesicles. The GV membrane composition used here was a modification of a DOPC/DPPC/cholesterol mixture known to form micrometer-scale liquid ordered and liquid disordered domains; we added lipids with PEG 2000 Da-modified headgroups. Osmotically induced budding of the ATPS-containing GVs led to structures where the PEG-rich and dextran-rich interior aqueous phases were in contact with different regions of the vesicle membrane. Liquid ordered (L o) membrane domains rich in PEG-terminated lipids preferentially coated the PEG-rich aqueous phase vesicle "body", while coexisting liquid disordered (L d) membrane domains coated the dextran-rich aqueous phase "bud". Membrane domain positioning resulted from interactions between lipid headgroups and the interior aqueous polymer solutions, e.g., PEGylated headgroups with PEG and dextran polymers. Heating resulted first in patchy membranes where L o and L d domains no longer showed any preference for coating the PEG-rich vs dextran-rich interior aqueous volumes, and eventually complete lipid mixing. Upon cooling lipid domains again coated their preferred interior aqueous microvolume. This work shows that nonspecific interactions between interior aqueous contents and the membrane that encapsulates them can drive local chemical heterogeneity, and offers a primitive experimental model for membrane and cytoplasmic polarity in biological cells.     

Mechanism of nitromethane liquid membrane oscillator containing sodium oleate

The oscillatory behavior of a liquid membrane oscillator with anionic surfactant was investigated in order to understand the oscillation mechanism at the molecular level. As a theoretical framework, an approach based on chemical kinetics laws has been used. The chosen system involved nitromethane with 2,2(')-bipyridine as liquid membrane. The aqueous donor phase contained sodium oleate and butanol, while sodium chloride was added to the aqueous acceptor phase. It was established that the oscillations take place exclusively at the aqueous acceptor phase/membrane interface. Therefore, liquid membrane oscillators with anionic surfactants behave the same way as oscillators with cationic surfactants as to the location of oscillations. An oscillation mechanism involving three stages is proposed and confirmed by numerical simulations. The oscillations of electrical potential differences between the two aqueous phases are produced by sudden adsorption and desorption of anionic surfactant in solvated form and butanol at the acceptor/membrane interface. The whole process is controlled by the slow diffusion of these species across the liquid membrane. The chaotic character of the oscillations was demonstrated by Lyapunov exponents obtained from the strange attractor of the system.     

Thioether-mediated copper transport through liquid membranes with the aid of redox reaction

A thioether-mediated copper transport with the aid of redox reaction was studied in a polymer-supported liquid membrane and in a liquid surfactant membrane. A photochemical generation of the redox potential led to a photo-assisted copper separation and concentration system. Tetradentate thioethers 1 and 2 (L) selectively extracted copper ion into organic solution in the presence of a reducing agent, and served as a copper-selective carrier in a liquid membrane system. In the polymer-supported organic liquid membrane system, the thioether was dissolved in the membrane phase which separated the two aqueous solutions of different redox potentials. The copper ion was extracted into the membrane phase by formation of the [Cu^IL]⁺ ? X^? type complex on the reducing solution interface and permeated through the membrane toward the oxidizing solution interface, where the complex was decomposed to release the copper(II) species into the oxidizing aqueous solution. The nature of the system was studied in detail under various operational conditions (redox agents, pairing anion X^?, coexisting metals, etc.) and compared with that of the previously reported Bathocuproine-mediated system. The transport system was extended to the water-in-oil-in-water emulsion system (liquid surfactant membrane), and the selective concentration of copper ion from dilute external aqueous solutions into inner stripping solutions was achieved. Photo-induced redox reactions, triethanolamine—acriflavine—methyl viologen—hv and glucose—titanium oxide—hv, were successfully coupled to the systems, leading to a photo-assisted copper transport in the polymer-supported liquid membrane as well as in the liquid surfactant membrane. Tentative explanations were given on the nature of the membrane transport reactions.     

Mechanism of a four-phase liquid membrane oscillator containing hexadecyltrimethylammonium bromide

The oscillatory behavior of a nitromethane based liquid membrane oscillator was investigated to contribute to the oscillation mechanism at the molecular level. At the beginning the system contains three phases: the aqueous donor phase in which the cationic surfactant, hexadecyltrimethylammonium bromide and ethanol are present and the aqueous acceptor phase made up by sucrose solution separated by the liquid membrane containing a constant amount of picric acid. During experiment a new phase x is created between the liquid membrane and acceptor phase. It was established that the oscillations take place at the membrane/phase x and the phase x/acceptor phase interfaces. Five basic regions can be distinguished in the oscillation pattern. The molecular events provoking the oscillations of electric potential difference between the two aqueous phases involve essentially the diffusion of hexadecyltrimethylammonium bromide and ion pairs formed by the cation of the surfactant and the picrate anion to the vicinity of the membrane/phase x interface, sudden adsorption of these ion pairs at this interface in noncatalytic and autocatalytic steps, desorption of ion pairs from the membrane/phase x interface into phase x, diffusion of ion pairs to the vicinity of phase x/acceptor phase interface, and sudden adsorption at this interface followed by desorption to the aqueous acceptor phase. It is shown by numerical simulations that the proposed mechanism may account for the observed oscillations and for the species distribution throughout the system as found experimentally. This four-phase system behaves like two coupled oscillators.     

Membrane protein isolation by in situ solubilization, partitioning and affinity adsorption in aqueous two-phase systems. Purification of the human type 1 11beta-hydroxysteroid dehydrogenase

Recently developed aqueous two-phase systems based on non-ionic detergents and polymers are suitable for the separation of membrane proteins. Moreover, within this relatively membrane protein "friendly" environment, changes in temperature can be controlled and stabilizing agents may be added to ensure integrity of the target protein during isolation. Here, we use aqueous two-phase partitioning for the isolation of membrane bound 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). Different detergents were used to find optimal conditions regarding solubilization and retaining target protein activity. We explored in situ solubilization by adding detergent directly to the aqueous two-phase system, as well as a batch metal affinity capture step of 6xHis tagged 11beta-HSD1 in the two-phase system. The use of detergent/polymer two-phase systems resulted in a specific enzyme activity of 3840 nmol mg(-1) min(-1) of the target membrane protein compared to a conventional purification protocol where a specific enzyme activity of 1440 nmol mg(-1) min(-1) was achieved.     

Permeation of metal ions through a series of two complementary supported liquid membranes

The permeation of Am³⁺ and Eu³⁺. through two composite supported liquid membranes, SLM, consisting of a series of two complementary SLMs, separated by an aqueous solution, has been studied. The first liquid membrane was a neutral membrane, i.e., a solution of a bifunctional neutral organophosphorous extractant in decalin. The second liquid membrane was an acidic membrane, i.e., a solution of bis(2-ethylhexyl)phosphoric acid in n-dodecane or of dinonylnaphthalene sulphonie acid in decalin. The solid support was a microporous polypropylene film. The composite SLM system had the sequence “Solution A — SLM(A) -Solution B — SLM(B) — Solution A”, where aqueous solution A promotes extraction of th the metal cations into SLM(A) and their stripping from SLM(B), and aqueous solution B promotes stripping of metal cations from SLM(A) and their extraction into SLM(B). SLM(A) and SLM(B) are a neutral or an acidic S/aVis or vice versa. The study has demonstrated that the single-stage character of SLM separations of metal ions in solution can be in principle overcome by repeating the composite SLM arrangement a number of times. The equations describing the concentration variations in the aqueous solutions which are adjacent to the acidic and neutral SLMs are also reported. They allow one to predict quantitatively the degree of enrichment of each aqueous solution as function of time and the degree of separation among different cations achievable with the composite SLM system. The overall permeability of the composite SLM system to a given cation is shown to be a function of the single-membrane permeability coefficients as well as of the volumes of the aqueous solutions and the SLM area.     

Separation of metals by liquid surfactant membranes containing crown ether carboxylic acids

A water-in-oil-in-water emulsion liquid membrane system is used to transport alkali metal and alkaline earth cations from an external alkaline aqueous source phase through an organic membrane containing a crown ether carboxylic acid and into the internal acidic aqueous phase of the emulsion droplet. The influence of varying the crown ether carboxylic acid structure upon the selectivity and efficiency of competitive metal ion transport is examined.     

Protein pre-fractionation in detergent-polymer aqueous two-phase systems for facilitated proteomic studies of membrane proteins

Pre-fractionation of a complex mixture of proteins increases the resolution in analytical separations of proteins from cells, tissues or organisms. Here we demonstrate a novel method for pre-fractionation of membrane proteins by a detergent-based aqueous two-phase system. Membrane proteins are strongly under-represented in proteomic studies based on two-dimensional electrophoresis (2-DE). As a model system, we have isolated mitochondria from the yeast Saccharomyces cerevisiae. Mitochondrial proteins were fractionated in an aqueous two-phase system consisting of the polymer poly(ethylene glycol) and either of two commonly used non-ionic detergents, Triton X-114 or dodecyl maltoside (DDM). Soluble proteins partitioned mainly to the polymer phase while membrane proteins were enriched in the detergent phase, as identified from one-dimensional electrophoresis (1-DE) and/or 2-DE followed by mass spectrometric analysis. Pre-fractionation was further enhanced by addition of an anionic detergent, sodium dodecyl sulfate, or a chaotropic salt, NaClO4, and by raising the pH in the system. The two-phase system pre-fractionation was furthermore combined with an alternative two-dimensional high-resolution separation method, namely ion-exchange chromatography and 1-DE. By this approach a larger number of membrane proteins could be identified compared to separation with conventional 2-DE. Thus, pre-fractionation of complex protein mixtures using the aqueous two-phase systems developed here will help to disclose larger proportions of membrane proteins in different proteomes.     

An unsegmented extraction system for flow injection analysis

In the system described, the two phases are fed into a module containing a PTFE membrane so that no segmentation takes place, i.e., each phase is fed to only on one dise of the membrane. The groove depth on the “aqueous” side of the membrane is 0.4 mm and on the “organic” side 0.8 mm. This latter groove is filled with a porous support of polyethylene. Caffeine, sodium dodecyl sulphate and sodium dioctylsulphosuccinate samples (40—500 μl) were injected into an aqueous carrier stream which was merged and mixed with an aqueous reagent before it was fed into the module. The maximum extraction efficiency varied with the flow rate but was in the range 8–18% and was obtained by injecting sample volumes larger than 400 μl. By injecting 40 μl of sample, the efficiency dropped by a factor of 1.5–7, depending on the character of the analyte. The system is suitable for coarse liquid-liquid extraction of concentrated samples because neither segmentation nor separation of the phases is required.     

一种新的液膜振荡体系的振荡规律

本文报道一种 新的液膜振荡体系.该体系的二水相分别是结晶紫的水溶液(含有一定浓度的醇)和蔗糖溶液,介于二水相之间的油相为2,6-二硝基苯酚的硝基苯溶液.本文对这一新的体系的液膜电势振荡机理作了初步的探讨.     

Study on the liquid membrane oscillation of water/oil/water system containing TTAB and picric acid

The liquid membrane oscillation of a novel water （aqueous tetradecyl trimethyl ammoniumbromide, TTAB and alcohol solution）/oil （picric acid in chloroform solution）/water （aqueous glucose solution） system was investigated. By using homemade device, the curves of various liquid membranes oscillation with different concentration of TTAB and picric acid, types of alcohol and other organic solvents at different temperature were measured. The results show that the water （aqueous 7 mmol/L of TTAB and 0.5 mol/L of n-propanol solution）/oil （0.5 mmol/L of picric acid in chloroform solution）/water （aqueous glucose solution） system performed sustained and stable oscillation at 30 ℃. And the novel system can recognise added amino acid.     

Studies on emulsion liquid membrane extraction of cephalexin

An experimental study on batch extraction of cephalexin using an emulsion liquid membrane system has been reported. The effects of surfactant, carrier and solute concentrations, phase volume ratio, stirring speed, and counterion concentration on the extraction rate were examined. Surfactant, carrier and diluent used were Span-80, Aliquat-336 and n-heptane–kerosene (1:1), respectively. Under the optimised experimental conditions, emulsion swelling was found to be marginal. By maintaining an appropriate pH gradient in the feed and receiving aqueous phase, facilitated transport could be realised. Selective separation of cephalexin from a mixture of 7-aminodeacetoxy cephalosporanic acid (7-ADCA) could be demonstrated in the emulsion liquid membrane system. A mathematical model based on mass transfer across aqueous boundary layer, interfacial chemical reaction and diffusion in the emulsion globule provides a reasonable fit of the experimental solute concentration versus time profiles in the emulsion liquid membrane system.     

Dynamic imaging of enzymatic events at polyelectrolyte-disrupted phospholipid membranes using liquid crystals

In this study, we employed a simple liquid crystal (LC)-based system to dynamically image enzymatic events at the aqueous/LC interface decorated with polyelectrolyte-disrupted phospholipid membranes. Since polyelectrolytes were shown to disrupt the arrangement of the self-assembled phospholipid monolayer and induced a dark-to-bright shift in the optical response of LCs that support the phospholipid membrane, we observed that the transfer of an aqueous solution of protease onto the polyelectrolyte-disrupted phospholipid membrane resulted in a gradual recovery of the optical response of LCs from bright to dark appearance. Due to the enzymatic event that occurs at the aqueous/LC interface, the generated polyelectrolyte fragments desorbed from the interface to the bulk solution. This led to the restoration of the disrupted phospholipid monolayer, which resulted in recovery of the optical response. These results suggest that the polyelectrolyte-decorated membrane-supported LCs could be potentially used to examine a range of biological interactions that involve polyelectrolytes. Furthermore, the LC-based system holds great promise for label-free and real-time investigation and detection of biomolecular interactions coupled to membrane disruption and restoration, which might have potential utility in the clinical diagnosis and treatment of membrane-associated disease.     

Extraction based on the flow-injection principle: Part 5. Assessment with a Membrane Phase Separator for Different Organic Solvents

Several membrane phase separators have been designed and tested for use in a flow-injection extraction manifold. The membrane is sandwiched between two pieces of perspex with grooves facing the membrane. A PTFE membrane with polyethylene backing proved to be most suitable. With this type of phase separator the total dispersion in the extraction system is less than that obtained with the conventional T-piece separator. Alcohols, alkanes, chlorinated hydrocarbons and aromatic solvents pumped at a flow rate of 0.5–1.0 ml min^-1 can be segmented with aqueous phase and later separated from it with a recovery of up to 95%. The organic phase passing through the detector flow cell is not contaminated by the aqueous phase to any measurable extent.     

Ionic rectification properties of a bipolar interface consisting of a cationic surfactant and cation-exchange membrane

A novel bipolar interface that consists of cationic surfactant and cation-exchange membrane was successfully prepared in an aqueous electrolyte system. This bipolar interface shows a ionic rectification behavior similar to that observed in bipolar membranes. However, different from bipolar membranes, this system has a total rectification behavior, where we cannot observe the occurrence of a water-splitting phenomenon, which always occurs in the bipolar membrane process under reverse bias conditions.     

Mathematical modeling of silver extraction by an emulsion liquid membrane process

A general physical model of a typical batch extraction system employing an emulsion liquid membrane process for the extraction of silver has been developed. The model takes into account the extraction reaction between the silver ion and the carrier molecules at the external interface, the diffusion of the complex in the membrane phase, the stripping reaction at the internal interface and the reaction of silver ion with the reagent, HCL, in the internal phase to yield silver chloride incapable of permeating through the membrane phase. In addition, the leakage of the internal aqueous phase to the external aqueous phase due to membrane breakage has been incorporated in this model. The batch extraction of silver using D2EHPA as a carrier has been carried out under various experimental conditions. The experimental data can be well explained by the present model.     

Membrane-based solvent extraction for selective removal and recovery of metals

A membrane-based solvent extraction process was developed for selective removal and recovery of metals from aqueous solutions. The process utilizes microporous membranes as an interface between an aqueous solution and organic solvents containing liquid ion exchangers. Metal ions are transported from the aqueous solution to the organic phase at the interface created in the pores of membrane. The organic solvent, which is loaded with metal ions in the extraction module, is regenerated in contact with the stripping solution in the stripping module. One important feature of this process is the stability of the membrane system, which results from using an aqueous—organic separator to remove aqueous solution from the organic circulating line. This process was evaluated for enrichment of copper using solvents containing LIX 64N. The process is applicable to selective recovery of metals from ore leachates or metal-containing wastewater.     

Effect of proton concentration on membrane potential across a weak amphoteric polymer membrane

An amphoteric membrane consists of both positively and negatively fixed charge groups chemically bound to the polymer chains. If the external solution is changed from alkali to acid, it is possible to obtain an experimental result in which the membrane potential changes from positive to negative through the isoelectric point. It was characterized by examining the relationship between membrane potential and proton concentration (pH) obtained from both experimental and theoretical considerations. The Nernst-Planck flux equation and the Donnan equilibrium theory were also solved for a four-component system combined with the dissociation constant, in order to discuss the pH dependence of membrane potential in a weak amphoteric membrane by comparing the experimental results with the calculated results. It was proven that the calculated results substantially deviated from the theoretical results despite a similar tendency. Such a deviation was caused by the fact that the original theory disregarded the activity coefficient and the ionic mobility, which were dependent on the fixed charge concentration in a membrane. The original theoretical model was modified by adding the effect of a fixed charge group to the activity coefficient and ionic mobility. The calculated results using the modified model explained well the experimental results if the parameter called charge effectiveness, phi, was introduced into the equations. Introduction of phi into the prediction of membrane potential was already done by Kobatake et al. in a system of a strong polyelectrolyte monopolar membrane/salt aqueous solution. In this study, it was proved that phi can also be introduced into a weak amphoteric polymer membrane/salt aqueous solution system. Finally it was also concluded that the Donnan equilibrium and the Nernst-Planck flux equation were still applicable for examining the transport phenomena for the system of a weak amphoteric charged membrane and electrolyte solutions at various pH.     

高温水溶液pH值原位测量系统与机理

研制了以氧化钇稳定氧化锆(YSZ)陶瓷薄膜电极为pH电极、外置压力平衡式Ag/AgCl电极为参比电极的高温高压水溶液pH值原位测量系统,测量了H₃BO₃\LiOH水溶液在473.15~573.15 K范围内的pH值,并与热力学计算得到的pH值比较。 结果表明,当温度高于548.15 K时,测量系统可以实现pH值的准确测量;而低于此温度时,由于YSZ陶瓷膜内阻过大,测得的pH值与理论计算值存在偏差,且随温度的降低,测量偏差增大。 讨论了该系统的pH值测量机理。