Evaluation of asymmetrical structure dialysis membrane by tortuous capillary pore diffusion model

The tortuous capillary pore diffusion model (TCPDM) has been used for estimating diffusive and pure water permeability from simple structure parameters such as pore diameter, surface porosity, wall thickness and tortuosity. The validity of this model for evaluation of homogeneous membrane has been already confirmed. Recently, there is a trend toward the use of asymmetrical dialysis membranes made of synthetic polymer such as poly(acrylonitrile) (PAN), polysulfone (PS) and a polyethersulfone polyarylate (PEPA) blend polymer. The purpose of the present study is to apply the TCPDM to evaluation of commercially available hollow-fiber dialysis membranes with asymmetrical structures by simplifying them to a double-layer membrane. The TCPDM is capable of estimating pore tortuosity of asymmetrical dialysis membranes having skin and supporting layers from data on membrane thickness, pore diameter, pure water permeability and water content. Values for diffusive permeability obtained by the TCPDM are in a good agreement with experimental data. This TCPDM model is useful for evaluation of not only homogeneous membrane but also asymmetrical membrane.     

Bi-ionic membrane potential across a liquid anion-exchange membrane containing triphenyltin chloride

Potentiometric selectivities of a liquid anion-exchange membrane containing triphenyltin chloride (TPTCl) to several inorganic anions were evaluated via measurements of the membrane potential of a bi-ionic system, also called bi-ionic membrane potential. Addition of TPTCl to the liquid anion-exchange membrane, based on the quaternary ammonium salt, gave rise to a quite different selectivity pattern from the so-called Hofmeister anion series observed for the liquid anion-exchange membrane. An additivity rule of the bi-ionic membrane potential was observed to hold for the liquid anion-exchange membrane containing TPTCl. Thus, the following multiple chain rule was derived for selectivity coefficients; k_1,n^pot = k_1,2^pot · k_2,3^pot … k_i,(i+1)^pot … k_n−1,n^pot where k_i,i+1^pot is the selectivity coefficient of the membrane for the (i + 1)th ion over the ith ion.     

Some factors in membrane structures on permselectivity for organic liquid mixtures

Control of permselectivity based on the structure of the microphase separation of graft copolymer membranes, improvement of ethanolpermselectivity by surface modification of polymer membranes, and enhancement of ethanol-permselectivity with improvements in the membrane separation technique for aqueous ethanol solutions are discussed.     

Continuous dialysis of hydrochloric acid and lithium chloride: permeability of anion-exchange membrane to chloride ions

A counter-current two-compartment dialyzer equipped with an anion-exchange membrane Neosepta-AFN was used to study dialysis of a hydrochloric acid and lithium chloride mixture. To quantify this process, several characteristics were calculated from the data obtained at steady state. First, the dialysis process was characterized by the acid recovery yield and rejection coefficient of salt, which were in the range of 61–98% and 62–94%, respectively (for HCl and LiCl concentrations from 0.1 to 1.0 kmol m^?3 and volumetric liquid flow rates from 8 × 10^?9 to 24 × 10^?9 m³ s^?1). Furthermore, this study proved that dialysis of an HCl + LiCl mixture can be quantified by a single characteristic, i.e., the permeability coefficient of the membrane to chloride ions, which is a function of the concentration of both the components in the feed.     

Purification of human chorionic gonadotropin hormone by anion-exchange high-performance liquid chromatography

Chromatographia - A high-performance liquid chromatography (HPLC) method was developed for the purification of 50mg crude human chorionic gonadotropin (HCG) hormone sample in one chromatographic...     

Speciation of arsenical species by anion-exchange and ion-pair reversed-phase liquid chromatography

Summary Speciation and quantitative analysis of arsenical compounds are performed by using high-performance liquid chromatography (HPLC) with direct UV detection. Ion chromatography has been used to separate mixtures of arsenical compounds (arsenite, MMA, DMA, arsenate) on an anion-exchange column using phosphate buffer (1 mmol/l, pH=5.3) as eluent. Ion -pair reversed-phase chromatography has been investigated to resolve mixtures of arsenite, arsenate, MMA, DMA, arsenobetaine and arsenocholine on an octadecyl-bonded silica column using water as mobile phase (pH=7.3) and tetrabutylammonium cation as ion-pairing reagent. The influence of several parameters (pH, the ion-pairing reagent concentration or the amount of methanol in the mobile phase) has been studied to determine the best chromatographic conditions.     

Transport of sulfuric acid through anion-exchange membrane NEOSEPTA-AFN

This paper deals with the determination of the membrane mass transfer coefficient for sulfuric acid in an anion-exchange membrane NEOSEPTA-AFN. This quantity has been determined on the basis of experiments carried out in a batch dialysis cell using the method of numerical integration of the basic differential equation describing the time dependence of sulfuric acid concentration and subsequent optimization procedure. The experiments carried out made it possible to calculate the membrane mass transfer coefficient for sulfuric acid over the concentration range from 0.1 to 1.9 kmol m⁻³ in the external solution.     

Extraction of molybdenum by a supported liquid membrane method

This is a report on the extraction of molybdenum(VI) ions using a supported liquid membrane, prepared by dissolving in kerosene, the extractant Alamine 336 (a long-chain tertiary amine) employed as mobile carrier. A flat hydrophobic microporous membrane was utilised as solid support. Appropriate conditions for Mo(VI) extraction through the liquid membrane were obtained from the results of liquid-liquid extraction and stripping partition experiments. The influence of feed solution acidity, the carrier extractant concentration in the organic liquid film and the content of strip agent on the metal flux through membrane were investigated. It was established that maximal extraction of metal is achieved at a pH 2.0 if sulphuric acid is used in the feed solution and at a pH value over 11.0 if Na₂CO₃ is used as strip agent. Moreover, the molybdenum extraction through membrane is enhanced when a 0.02 mol l⁻¹ content of the amine carrier in the organic phase is used. The present paper deals with an equilibrium investigation of the extraction of Mo(VI) by Alamine 336 and its permeation conditions through the liquid membrane, and examines a possible mechanism of extraction.     

Extraction of glyphosate by a supported liquid membrane technique

The possible application of the supported liquid membrane (SLM) technique for the extraction of glyphosate is presented. For the extraction of this compound the SLM system has been applied with utilisation of Aliquat 336 as a cationic carrier incorporated into the membrane phase. The extraction efficiency of glyphosate [N-(phosphonomethyl)glycine] is dependent on the donor phase pH, carrier concentration in the organic phase and NaCl concentration in the acceptor phase. The optimal extraction conditions are: donor phase pH>11, acceptor phase of 2 M NaCl solution and the organic phase composed of 20% (w/w) Aliquot 336 solution in di-hexyl ether. Counter-coupled transport of chloride anions from the acceptor phase to the donor phase is a driving force of the mass transfer in this system.     

Preparation of S-acetylthioglycoloyl insulins based on separation by anion-exchange high-performance liquid chromatography.

A method for the preparation of insulin derivatives having protected sulfhydryl group(s) on definite site(s) on the molecule which uses anion-exchange high performance liquid chromatography on a TSKgel DEAE-2SW column for separation is described. Porcine insulin reacts with N-succinimidyl S-acetylthioacetate to afford four species of insulin derivatives that have S-acetylthioglycoloyl group(s) at: i) Gly(A1), ii) Gly(A1) and Phe(B1), iii) Gly(A1) and Lys(B29), and iv) Gly(A1), Phe(B1) and Lys(B29) positions. An insulin derivative which has a group at the Lys(B29)-position is prepared by the S-acetylthioglycoloylation of Gly(A1), Phe(B1)-dicitraconyl insulin followed by decitraconylation. The five derivatives are readily deacetylated with hydroxylamine to yield the corresponding sulfhydryl insulin derivatives.     

Determination of hexavalent chromium in welding fumes by GFAAS after liquid anion-exchange separation

Summary The interferences due to the presence of large amounts of atoms such as iron, sodium, cadmium, magnesium and potassium on the ETA-AAS determination of trace amounts of chromium(VI) in welding fumes are discussed. An ion-exchange liquid extraction separation procedure is proposed to overcome these interactions. Results obtained on international standards of welding fumes, distributed in two round robin experiments, are also presented.

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Bestimmung von Chrom(VI) in Schweißereidämpfen nach Abtrennung mit Hilfe eines flüssigen IonenaustauschersUntersuchung der Störungen

     

Evaluation of coupled transport across a liquid membrane as an analytical preconcentration technique

When two aqueous solutions are separated by a liquid membrane that contains a complexing agent which is a conjugate base of a weak acid, a metal ion can be transported from the solution of the higher pH against its concentration gradient into the more acidic solution. With Cu(II) as the analyte and a liquid membrane consisting of a mixture of oximes dissolved in kerosene, enrichment factors for a prescribed dialysis time in a simple experimental apparatus were nearly independent of Cu(II) concentration over the range 10(-4)-10(-7)M. With 0.1M hydrochloric acid as the receiver, the enrichment factor was independent of ionic strength and of sample pH in the range 4-9. The effect of sample pH on the interference of Fe(III) was examined. With a pH-2.5 formate buffer, the enrichment factor for Cu(II) decreased as the Fe(III) concentration increased, but in a pH-9.3 ammonium buffer, 0.14 mM Fe(III) did not interfere with the transport of Cu(II) from a 16muM copper sample.     

Emulsion liquid membrane extraction of zinc by a hollow-fiber contactor

Emulsion liquid membranes (ELMs) can contribute to process intensification of zinc extraction, by significantly reducing the solvent and carrier requirements in comparison with conventional solvent extraction. Di(2-ethylhexyl)phosphoric acid (D2EHPA) was used as a highly selective carrier for the transport of zinc ions through the emulsified liquid membrane. The hollow-fiber extractor appears to offer significant advantages over conventional liquid–liquid contactors for this separation because emulsion leakage and swell are practically eliminated even when treating high concentration feeds. Various hydrodynamic and chemical parameters, such as variation in feed pH; zinc concentration in feed; variation in concentrations of D2EHPA; variation in feed/emulsion volume ratios and variation in feed and emulsion flow rates, were investigated. The content of sulfuric acid as an internal did not show in the studied range any significant influence on zinc extraction through the ELM, although a minimum hydrogen ion concentration is suggested in the internal aqueous solution to ensure acidity gradient between both aqueous phases to promote the permeation of zinc ions toward the internal phase. The experimental mass-transfer coefficients have shown a stronger dependence on hydrodynamic conditions in both the external feed phase and emulsion among the parameters studied. For emulsion flow rate, mass-transfer coefficient increased from 16.3 × 10⁻⁶ m/s at 200 ml/min to 31.2 × 10⁻⁶ m/s at 640 ml/min. Significant increasing in mass-transfer coefficient observed with increasing aqueous flow rate from 9.7 × 10⁻⁶ m/s at 170 ml/min to 37.2 × 10⁻⁶ m/s at 740 ml/min. The overall mass-transfer coefficient increases from 12 × 10⁻⁶ m/s at 2% D2EHPA to 28 × 10⁻⁶ m/s at 8% D2EHPA. This means that this process is chemically controlled and the interfacial resistance has a more significant role in the extraction of zinc by emulsion liquid membrane through hollow-fiber contactor. From the results obtained, it seems that the diffusion processes in aqueous feed phase and the membrane phase have the same importance as the chemical process.     

Determination of niacin in infant formula by solid-phase extraction and anion-exchange liquid chromatography.

A peer-verified, solid-phase extraction (SPE)/anion exchange liquid chromatographic method is presented for the determination of niacin in milk-based and soy-based infant formula. Analysis is in 3 steps: test sample digestion, extraction/cleanup, and liquid chromatography (LC). Digestion uses a standard AOAC digestion procedure that involves autoclaving at 121 degrees C for 45 min in (1 + 1) H2SO4 to free endogenous niacin from protein and to convert added niacinamide to niacin. The digest solution is adjusted to pH 6.5 with 7.5M NaOH. Acidification to pH <1.0 with (1 + 1) H2SO4 precipitates the protein. The clarified solution is then filtered, and the filtrate is brought to volume. SPE of niacin is accomplished by passing an aliquot of the digest solution through an aromatic sulfonic acid-SPE (ArSCX-SPE) column. After the column is washed with methanol and water to remove extraneous material, the niacin is eluted with 0.25M sodium acetate/acetic acid buffer at pH 5.6. An anion-exchange polystyrene-divinylbenzene column with 0.1 M sodium acetate/acetic acid buffer at pH 4.0 is used for LC. Niacin is determined by UV detection at 260 nm. A standard curve is prepared by passing known amounts of niacin through the ArSCX-SPE columns used for niacin extraction. The following values for x and relative standard deviation (RSD) were obtained for National Institute of Standards and Technology Standard Reference Material (NIST SRM) 1846 Infant Formula with a certified value for niacin of 63.3 +/- 7.6 microg/g: Submitting laboratory.-- x = 59.7 +/- 4.0 microg/g; RSD = >6.7%; confidence interval (CI) = +/- 1.4 microg/g; n = 27. Peer laboratory.--x = 56.6 +/- 6.6 microg/g; RSD = >11.7%; CI =+/- 4.1 microg/g; n = 8.     

Analysis of diffusion models for protein adsorption to porous anion-exchange adsorbent

The ion-exchange adsorption kinetics of bovine serum albumin (BSA) and gamma-globulin to an anion exchanger, DEAE Spherodex M, has been studied by batch adsorption experiments. Various diffusion models, that is, pore diffusion, surface diffusion, homogeneous diffusion and parallel diffusion models, are analyzed for their suitabilities to depict the adsorption kinetics. Protein diffusivities are estimated by matching the models with the experimental data. The dependence of the diffusivities on initial protein concentration is observed and discussed. The adsorption isotherm of BSA is nearly rectangular, so there is little surface diffusion. As a result, the surface and homogeneous diffusion models do not fit to the kinetic data of BSA adsorption. The adsorption isotherm of gamma-globulin is less favorable, and the surface diffusion contributes greatly to the mass transport. Consequently, both the surface and homogeneous diffusion models fit to the kinetic data of gamma-globulin well. The adsorption kinetics of BSA and gamma-globulin can be very well fitted by parallel diffusion model, because the model reflects correctly the intraparticle mass transfer mechanism. In addition, for both the favorably bound proteins, the pore diffusion model fits the adsorption kinetics reasonably well. The results here indicate that the pore diffusion model can be used as a good approximate to depict protein adsorption kinetics for protein adsorption systems from rectangular to linear isotherms.     

Purification of ascitic fluid-derived murine monoclonal antibodies by anion-exchange and size-exclusion high-performance liquid chromatography

Ascitic fluid-derived murine monoclonal antibodies (MoAbs) of immunoglobulin (Ig) M and IgG isotypes (IgG1 and IgG2a subisotypes) were previously prepared against an isolate of Actinobacillus sp (CAs8C) for the purpose of identifying and characterizing outer membrane antigens on this bacterium. An attempt was made to purify these MoAbs by anion-exchange and size exclusion high-performance liquid chromatography (HPLC). Hybridomas producing the IgG1 and IgG2a MoAbs posed unique difficulties in that they also secreted irrelevant IgG2b MoAbs that were present in the ascitic fluids. Anion-exchange chromatography (Protein-Pak DEAE-5PW column), with a simultaneous change in gradients of pH and ionic strength, was used to purify IgG and as a first step in the purification of IgM. There was good separation of IgG2b from IgG2a, but not from IgG1. Size-exclusion chromatography (Protein-Pak 300 SW column) was required to complete the purification of IgM. The presence of MoAbs in the HPLC fractions was confirmed by discontinuous gradient polyacrylamide gel electrophoresis (denatured and either reduced or non-reduced conditions) and the enzyme-linked immunosorbent assay. HPLC-purified MoAbs were free from transferrin and albumin and retained their specificity for As8C.