Stripping Analysis of Trace Metals at a Flow-Through Reticulated Vitreous Carbon Electrode after the Preconcentration by Supported Liquid Membrane Technique

Abstract

The performance of a flow-through mercury coated reticulated vitreous carbon (RVC) electrode in the potentiometric stripping analysis (PSA) of trace metals has been examined. A wall-jet glassy carbon cell was used for the comparative experiments. Experimental parameters influencing the stripping signals have been optimised in order to use the stripping analysis after the preconcentration and matrix isolation by supported liquid membrane (SLM) technique. The SLM with di-2-ethylhexyl-phosphoric acid (DEHPA) as the extractant in the membrane liquid for proton driven transport of trace metals across the membrane has been chosen. Results presented for lead determination in river water demonstrate the analytical advantages of coupled technique SLM-PSA.     

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.     

Geraniol Based Side Chain Liquid Crystalline Polymer: Synthesis and Characterization

Side chain liquid crystalline (SCLC) polysiloxane polymer with a geraniol mesogenic group and polymethylene spacers were prepared, and their properties were compared with those of an equivalent SCLC polymer, SCLCP's, with phenyl benzoate mesogenic group. The phase behavior was studied by differential scanning calorimetry (DSC) and optical polarizing microscopy (OPM). The DSC curve showed a clear melting temperature and isotropization at 72 and 148°C, respectively, with a glass transition at 25°C. The observation of a fan‐shaped texture confirms the presence Smectic A phase under an optical polarized microscope.     

Electrically-induced optical storage effects in smectic polysiloxanes A variable transmission device

Abstract

Changes in the optical transmission induced by electric fields have been studied in a smectic side-chain polysiloxane liquid crystal. The transmission varied from effectively zero, for a highly scattering (opaque) texture, to total, for a homeotropic texture, on increasing the applied voltage across the material. The field-induced textures were durably stored in the smectic phase, enabling the order parameter of the side groups to be studied by dielectric relaxation measurements. For the highly transparent texture, a side group order parameter of 0-92 has been observed.     

Supported liquid membrane based loading technique for thermal ionization mass spectrometry: an application to plutonium isotopic composition and concentration determination

Supported liquid membrane (SLM) was prepared by immobilizing the extractant tricaprylmethyl ammonium chloride (Aliquat-336) into the microporous poly(propylene) membrane. The formed SLM with optimize composition was found be selective toward Pu⁴⁺ ions over UO₂²⁺ and Am³⁺ ions in a wide range of high acid concentrations (3–7 mol L^?1 HNO₃). The composition of SLM was optimized by using varying proportions of Aliquat-336 with solvents/diluents such as dioctyl phthalate (DOP), 2-nitrophenyl octyl ether and tris(2-ethylhexyl) phosphate. Among these diluents, DOP was found to be stable and causing uniform distribution of the extractant on the membrane. The surface morphology was characterized by atomic force microscopy. Stability and change in physical structure of SLM was characterized by capillary flow porometry. The Pu pre-concentrated in SLM was used to find out isotopic composition and concentration of the plutonium with help of thermal ionization mass spectrometry. The SLM was found to be stable and amenable to routine analyses.     

Transport of carbonate ions through supported liquid membrane by using Alamine 336 and trioctylphosphine oxide as carriers

Abstract

Transport studies were carried out for carbonate ions through supported liquid membrane (SLMs) by using Alamine 336 and trioctylphosphine oxide (TOPO) as carriers. Experimental variables were investigated, such as concentration of carbonate ion (10^?5 to 4×10^?2 M), carriers (10^?5 to 10^?1 M), and alkali (0.01–0.5); and stirring speed (50–150 rpm) of bulk solutions. The use of combined carriers Alamine 336 and TOPO shows a synergic transport of carbonate ions. The stability of the SLM system in relation to the transport of carbonate ions has been studied. The enrichment of carbonate ions (10^?6 to 4×10^?2 M) from the dilute solution was explored. The different combinations of amines with TOPO show synergic permeability of the carbonate ions through SLM system.     

Optical resolution of various amino acids using a supported liquid membrane encapsulating a surfactant-protease complex

We have encapsulated a surfactant-protease complex (the main protease used being alpha-chymotrypsin) in an organic phase of a supported liquid membrane (SLM) for the optical resolution of various amino acids. L-Isomers of amino acids were enantioselectively permeated through the SLM. The mechanism of the amino acid permeation through the SLM was considered to be as follows; an L-amino acid was enantioselectively esterified with ethanol by a surfactant-protease complex encapsulated in the SLM, and the resulting L-amino acid ethyl ester dissolved into the organic phase of the SLM and diffused across the SLM. Another surfactant-alpha-chymotrypsin complex in the receiving phase catalyzed ester hydrolysis to produce the initial L-amino acid and ethanol, which are water-soluble. Thus, the L-amino acid was selectively transported to the receiving phase through the SLM on the basis of the molecular recognition of the surfactant-protease complex in the SLM. It was found that the catalytic activity and enantioselectivity of the surfactant-protease complex governed the permeate flux of amino acids and the enantiomeric excess in the membrane separation.     

Electro membrane extraction of biological anions with ion chromatographic analysis

A simple and sensitive single step electro membrane extraction (EME) procedure was demonstrated for biological organic anions with determination by ion chromatography (IC). Nitrite, adipate, oxalate, iodide, fumarate, thiocyanate and perchlorate were extracted from aqueous donor solutions, across a supported liquid membrane (SLM) consisting of methanol impregnated in the walls of a porous polypropylene membrane bag and into an alkaline aqueous acceptor solution in the lumen of the propylene envelope by the application of potential of 12 V applied across the SLM. The acceptor solution was analyzed by IC. Parameters affecting the extraction performance such as type of SLM, extraction time, pH of the donor and acceptor solution, and extraction voltage were studied. The most favorable EME conditions were methanol as the SLM, extraction time of 5 min, pH of acceptor and sample solutions of 12 and 4, respectively, and a voltage of 12 V. Portable 12 V batteries were used in the study. Under these optimized conditions, all anions had enrichment factors ranging from 3.6 to 36.2 with relative standard deviations (n = 3) of between 6.6 and 17.5%. Good linearity ranging from 0.1 to 10 μg mL⁻¹ with coefficients of correlation (r) of between 0.9981 and 0.9996 were obtained. The limits of detection of the EME-IC method were from 0.01 to 0.14 μg mL⁻¹. The developed methodology was applied to amniotic fluid samples to evaluate the feasibility of the method for real applications.     

Intensification of gadolinium(III) separation by effective utilization of nanoliquids in supported liquid membrane using Aliquat 336 as carrier

A supported nanoliquid membrane was developed to improve the separation of rare metal ion gadolinium (Gd) from nitrate solution medium. The nanoliquid membrane was prepared by dispersion of nanoparticles in organic phase and Aliquat 336 was applied as the carrier. TiO₂ and SiO₂ as hydrophobic and hydrophilic nanoparticles were effectively incorporated in the supported liquid membrane (SLM) system and the effect of size, concentration, and type of nanoparticle in the SLM were evaluated. A membrane phase of 0.015 M Aliquat-336 in kerosene and 0.04 wt% of SiO₂ with the size of 15 nm was found to have the highest permeability coefficient of 12.57?×?10^?5 m/s and enhanced the permeability coefficient by 28.2%. Hydrophobicity and hydrophilicity of the nanoparticles were observed to have remarkable effects on the permeation of the SLM system and concluded that the hydrophobic nanoparticle was more desirable. Results showed that the solid supported pore’s blockage and aggregation of nanoparticles could bring adverse effects at a high nanoparticle concentration at this SLM configuration. The stability tests were conducted over ten cycles of separation and the supported nanoliquid membrane had slight reduction of permeation during the test.     

Highly enantioselective separation using a supported liquid membrane encapsulating surfactant-enzyme complex

We developed a highly enantioselective separation system for the optically active compounds, (S)-ibuprofen and l-phenylalanine, from their racemic mixtures by employing a supported liquid membrane (SLM) encapsulating a surfactant-lipase complex (or a surfactant-alpha-chymotrypsin complex). In the present system, enzymes encapsulated in the liquid-membrane phase effectively drove the enantioselective transport of optically active compounds through the SLM. This novel SLM allowed high enantioselectivity (ee over 91%) in the optical resolution of racemic ibuprofen and phenylalanine.     

Enzyme-facilitated enantioselective transport of (S)-ibuprofen through a supported liquid membrane based on ionic liquids

Coupling lipase reactions with a supported liquid membrane (SLM) based on ionic liquids showed facilitative and selective permeation of (S)-ibuprofen through the SLM, indicating successful optical resolution of a racemic mixture using the enzyme-facilitative SLM.     

Facilitated transport of copper(II) across supported liquid membrane and polymeric plasticized membrane containing 3-phenyl-4-benzoylisoxazol-5-one as carrier

The potential of 3-phenyl-4-benzoylisoxazol-5-one (HPBI) as metal extractant has been evaluated for the first time for Cu(II) transport from aqueous nitrate solutions by supported liquid membrane (SLM) in the solvents chloroform, 2-nitro phenyl octyl ether (NPOE) and dodecyl nitro phenyl ether (DNPE). The efficiency of the membrane transport was optimized as a function of pH, temperature, aqueous phases and membrane composition. It follows the sequence CHCl₃ > DNPE > NPOE. The results suggested that the transport mechanism was mainly controlled by the diffusion of the Cu(PBI)₂ complex in the membrane core. A comparative investigation of Cu(II) transport ions has been made between SLM and polymeric plasticized membrane (PPM), containing HPBI with NPOE and DNPE as organic solvents or plasticizers in order to evaluate the feasibility of PPM with HPBI.     

Supported Liquid Membrane Enrichment Studies of Natural Water Samples Applied to Liquid Chromatographic Determination of Triazine Herbicides

Abstract

A method for sample work-up and enrichment using Supported Liquid Membrane (SLM) and liquid chromatographic determination of triazine herbicides in natural waters was investigated. A porous PTFE membrane was impregnated with a water immiscible organic solvent, forming a barrier between two aqueous phases. With a flowing donor and a stagnant acceptor solution, an enrichment of the triazines was obtained. The various factors that influence the extraction efficiency and selectivity of the extraction procedure were experimentally studied. The obtained results were in good agreement with the developed theoretical model. The pH of the acceptor solution was found to be the critical limiting factor in obtaining higher extraction efficiencies and led to an extraction efficiency decrease with an increase in enrichment time. By increasing both the trapping capacity of the acceptor solution and the donor flow rate, the method detection limit of the triazines ranged from 0.03 to 0.16 μgL^?1 in natural waters with 20 minutes extraction time.     

Effect of Doping Silica Gel Layers with TiOTi-Chains and Cu2+-Ephedrine on the Sensitivity of the Layers to Gases

In this paper the interaction of polysiloxane and TiOTi-doped polysiloxane gel layers containing Cu²⁺-ephedrine (CuEP) with carbon dioxide, nitrogen and water is investigated. This interaction is studied through changes of the output optical power from an optical fiber coated with the investigated gel layer. The layers are prepared with sols based on tetraethoxysilane and titanium isopropoxide, isopropanol, acetylacetone and Cu²⁺-ephedrine by the repeated dip-coating method. The applied gel layers are dried at 70°C.Spectral and temporal changes of the output optical power due to effect of the tested gases are measured. The measurements show big changes of the output optical power of fibers coated with CuEP-doped silica gel layers in a wavelength range from 400 to 700 nm, which is in relation with spectral effects of CuEP in alcoholic solutions. Relatively lower changes of the attenuation spectra without any attenuation band are found in the spectra of TiOTi-doped siloxane gel layers containing CuEP. The angular distributions of the output optical power of the coated fibers indicate high optical losses of the layers.     

Continuous flow liquid membrane extraction: a novel automatic trace-enrichment technique based on continuous flow liquid-liquid extraction combined with supported liquid membrane

Combining the continuous flow liquid-liquid extraction (CFLLE) and supported liquid membrane (SLM) extraction, a novel aqueous-aqueous extraction technique that we termed continuous flow liquid membrane extraction (CFLME) is developed for trace-enrichment. The analyte was firstly extracted into the organic phase in the CFLLE step, then transported onto the organic liquid membrane that formed on the surface of the micro porous membrane of the SLM equipment. Finally, it passed through the liquid membrane and was trapped by the acceptor. Aspects related to CFLME were studied by using dichloromethane as liquid membrane, and sulfonylurea herbicides as model compounds. An enrichment factor of over 1000 was obtained when 10 μg l⁻¹ of MSM was enriched for 120 min by this technique. The drawbacks of only a few organic solvents can be selected as liquid membrane with a limited lifetime in SLM operation was overcome. In this CFLME method, almost all solvents that used in the conventional liquid-liquid extraction (LLE) can be adopted and the lifetime of liquid membrane is no longer a problem.     

Optical Urea Biosensor Based On Ammonium Ion Selective Membrane

ABSTRACT

An optical urea biosensor was developed by immobilizing an urease enzyme layer on a thin ammonium-selective polymer membrane. The ammonium optical membrane utilized dichlorofluorescein octadecyl ester (DCFOE) as anionic chromophore and nonactin as neutral ionophore. The urease layer was coated on the top of the ammonium layer by gelatin entrapment combined with glutaradehyde cross-linking. Hydrolysis of urea catalyzed by urease produced ammonium ion, which was extracted into the-polymer film to form complexes with nonactin. A proton was released which resulted in a color change of the optical membrane due to charge neutrality principle. The biosensor     

New hydrocarbon side chain liquid crystalline polysiloxane polymers: Synthesis,characterization, and thermotropic behavior

A series of new and high-purity hydrocarbon liquid crystal monomers were synthesized through the acylation reaction, deoxygenation reaction, and Grignard reaction. ¹H-NMR spectra and elemental analyses were used to examine their purity. The liquid crystalline polysiloxane polymers were obtained by grafting the monomers onto poly(methylhydrosiloxane). The thermal transition temperature, mesomorphic properties, and mesophase textures of the monomers and the polymers were determined by differential scanning calorimetry (dsc), polarized optical microscopy, and X-ray diffraction analysis. Moreover, we observed the even–odd effect of the smectic/isotropic transition temperature with the length variation of the substituents. In this study, we found by X-ray diffraction that the liquid crystalline polysiloxane polymers undergo a transition from smectic B to smectic E mesophase. However, dsc has difficulty detecting the phase transition process. By considering the spin–lattice relaxation time (T₁), we can systematically explain the relation between the flexibility of the substituent with the smectic/isotropic transition temperature. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2849–2863, 1998     

Optical Sensing Membrane Based on Tetrabromophenolphthalein Ethyl Ester for the Determination of Cationic Surfactants

Abstract

An optical sensing membrane for detection of cationic surfactants was developed. The optical sensing membrane is 2‐nitrophenyl octyl ether‐plasticized poly(vinyl chloride) membrane incorporating tetrabromophenolphthalein ethyl ester (TBPE). The response of the optical membrane to cationic surfactants was a result of extraction of cationic surfactant into the PVC membrane. The protonated TBPE deprotonates forming an ion associate with the extracted cationic surfactant; simultaneously, the deprotonation of the TBPE is accompanied by a spectral change. Namely, the extracted cationic surfactant changes color of the membrane from yellowish green to blue (absorption maximum: 622 nm). The optical membrane responds to cationic surfactants such as Zephiramine and cetyltrimethylammonium bromide in the concentration range from 1 µM to 100 µM.     

Multistage separation of metal ions with a series of composite supported liquid membranes

The possibility of performing multistage separations of metal cations, present at low concentrations in aqueous solutions, using a series of composite supported liquid membranes (SLM), interposed between compartments containing identical aqueous electrolyte solutions, is discussed. The multistage separation of Eu³⁺. from Am³⁺ and of Sm³⁺ from Nd³⁺ and Ce³⁺ is theoretically analyzed. A single separation stage, using a thin, three-layer asymmetrical composite SLM, which allows differential permeation of Eu³⁺. and Am³⁺, is described and experimentally studied. The composite SLM consists of a 1 mm thick aqueous slab sandwiched between acidic and neutral supported liquid membranes. The results demonstrate that the permeation of each cation through the thin composite SLM can be described by a single permeation parameter which is equal to the permeability coefficient through the first acidic supported liquid membrane of the composite layer.