Strong Cation Exchange Membrane Research Articles

Performance Comparison of a Laterally-Fed Membrane Chromatography (LFMC) Device with a Commercial Resin Packed Column.

The use of conventional membrane adsorbers such as radial flow devices is largely restricted to flow-through applications, such as virus and endotoxin removal, as they fail to give acceptable resolution in bind-and-elute separations. Laterally-fed membrane chromatography or LFMC devices have been specifically developed to combine high-speed with high-resolution. In this study, an LFMC device containing a stack of strong cation exchange membranes was compared with an equivalent resin packed column. Preliminary characterization experiments showed that the LFMC device had a significantly greater number of theoretical plates per metre than the column. These devices were used to separate a ternary model protein mixture consisting of ovalbumin, conalbumin and lysozyme. The resolution obtained with the LFMC device was better than that obtained with the column. For instance, the LFMC device could resolve lysozyme dimer from lysozyme monomer, which was not possible using the column. In addition, the LFMC device could be operated at lower pressure and at significantly higher flow rates. The devices were then compared based on an application case study, i.e., preparative separation of monoclonal antibody charge variants. The LFMC device gave significantly better separation of these variants than the column.

Enhancing the efficiency of disc membrane chromatography modules by using a flow directing layer

Disc membrane chromatography modules are widely used for laboratory-scale protein separations. These have high radial to axial aspect ratios, with the inlet and the outlet being located at the centre. This results in a huge variability in flow path lengths. Also, the radial velocity in the feed side header decreases very significantly in an outward direction, while that in the permeate side header increases in an inward direction. Therefore, the flow paths closer to the axis of the membrane disc have higher average velocity compared to those closer to the periphery. Consequently, the solute residence time distribution within the disc membrane chromatography module is very large, which results in broad flow-through and eluted peaks and early breakthrough of bound solutes. In this paper, we discuss a simple but effective solution to this problem which involves the incorporation of a flow directing layer (FDL) within the membrane module. The FDL could be placed either in the front or at the rear of the membrane disc. The presence of FDL results in equalization of path lengths within the module, leading to narrowing of residence time distribution, and thereby improvement in separation efficiency. Modules housing strong cation exchange membrane discs having two different bed volumes of 0.4 mL (40 mm diameter) and 4.7 mL (60 mm diameter) were designed and fabricated in-house. The impact of using FDL on both the front side (F-FDL) and the rear side (R-FDL) was investigated. The separation efficiency of the membrane modules was assessed using salt tracer experiments, breakthrough protein binding, and ternary protein separation carried out in the bind-and-elute mode. The results confirmed that the use of the FDL significantly enhanced the separation efficiency. In addition to membrane chromatography, this approach of using an FDL could be extended to other membrane disc based modules such as in-line and syringe filters and membrane reactors.

Comparison of Membrane Chromatography and Monolith Chromatography for Lactoferrin and Bovine Serum Albumin Separation

These last few decades, membranes and monoliths have been increasingly used as stationary phases for chromatography. Their fast mass transfer is mainly based on convection, which leads to reduced diffusion, which is usually observed in resins. Nevertheless, poor flow distribution, which causes inefficient binding, remains a major challenge for the development of both membrane and monolith devices. Moreover, the comparison of membranes and monoliths for biomolecule separation has been very poorly investigated. In this paper, the separation of two proteins, bovine serum albumin (BSA) and lactoferrin (LF), with similar sizes, but different isoelectric points, was investigated at a pH of 6.0 with a BSA-LF concentration ratio of 2/1 (2.00 mg·mL−1 BSA and 1.00 mg·mL−1 LF solution) using strong cation exchange membranes and monoliths packed in the same housing, as well as commercialized devices. The feeding flow rate was operated at 12.0 bed volume (BV)/min for all devices. Afterward, bound LF was eluted using a phosphate-buffered saline solution with 2.00 M NaCl. Using membranes in a CIM housing from BIA Separations (Slovenia) with porous frits before and after the membrane bed, higher binding capacities, sharper breakthrough curves, as well as sharper and more symmetric elution peaks were obtained. The monolith and commercialized membrane devices showed lower LF binding capacity and broadened and non-symmetric elution peaks.

Preparation of high-capacity strong cation exchange membrane for protein adsorption via surface-initiated atom transfer radical polymerization

Membranes have an increasingly important niche in the isolation and purification of biomolecules. In this work, a strong cation exchange membrane with high capacity was prepared via surface-initiated atom transfer radical polymerization (SI-ATRP). An initiator was first anchored to the surface of a regenerated cellulose (RC) membrane, and then poly(sodium 4-styrenesulfonate) (poly(NASS)) was grafted onto the surface of the membrane via SI-ATRP, affording an ion exchange membrane with the sulfonate as the exchange group. The grafting degree was controlled by varying the ATRP reaction time. The results from attenuated total reflectance Fourier-transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) indicated that poly(NASS) was successfully grafted onto the membrane. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrated that the surface morphology exhibits a significant change as a result of the grafting reaction. The water flux measurement illustrated that the surface modification decreased the pore sizes of the membrane to some extent. Lysozyme was used as a model protein to evaluate the adsorption properties of the modified membranes under static and dynamic conditions. The results demonstrated that the protein adsorption capacities increased with increasing ATRP reaction time and could reach a maximum capacity of 138.3mg/mL and 92.9mg/mL for static and dynamic adsorption, respectively.

Ion-Exchange Membrane Chromatography Method for Rapid and Efficient Purification of Recombinant Baculovirus and Baculovirus gp64 Protein

Significant progress in the application of baculoviral vectors for gene delivery into mammalian cells calls for the development of powerful methods for virus purification and concentration. We report here a novel and efficient method based on membrane chromatography to prepare baculoviral stocks. On a strong cation-exchange membrane unit, baculovirus in insect cell culture supernatants was captured at a flow rate of 3 ml/min and efficiently eluted at the same flow rate with a physiological buffer containing 150 mM NaCl as a desorption reagent. The procedure allowed for a final recovery of 78% of infective viral particles from the original supernatant and 30-fold enrichment. The high purity of the viral preparation was demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Baculovirus gp64 proteins could be purified by the same method, indicating the importance of the protein in mediating the binding of baculovirus to the cation-exchange membrane. The method developed should be suitable for preparing baculoviral stocks, and probably other gp64-pseudotyped viral vectors, for gene therapy applications.

Application of a cellulose phosphate ion exchange membrane as a binding phase in the diffusive gradients in thin films technique for measurement of trace metals

The technique of diffusive gradients in thin films (DGT) is a newly developed analytical technique capable of measuring in situ concentrations of trace metals in the environment. The technique employs a thin film diffusive hydrogel (with well-defined diffusion properties) in contact with a binding phase capable of binding metal ions of interest. In this work, we demonstrate, for the first time, the use of a commercially available solid ion exchange membrane (Whatman P81) as the binding phase in DGT analysis. The cellulose phosphate-based Whatman P81 membrane is a strong cation exchange membrane. Its performance characteristics as a new binding phase in DGT measurement of Cu 2+ and Cd 2+ were systematically investigated. Several advantages over the conventional ion exchange resin-embedded hydrogel binding phases used in DGT were observed including simple preparation, ease of handling, and reusability. The binding capacities of the material to various metal ions were examined both collectively and individually. The binding phase preferentially binds to transition metal ions rather than matrix ions such as potassium, sodium, calcium and magnesium, which are competitive species in natural waters. Within the optimum pH range (pH 4.0–9.0), the maximum non-competitive binding capacities of the membrane for Cu 2+ and Cd 2+ were 3.22 and 3.07 μmol cm −2, respectively. The suitability of the new membrane–based binding phase for DGT applications was validated experimentally. The experimental results demonstrated excellent agreement with theoretically predicted trends. The measurement was not degraded after four consecutive reuses of the cellulose phosphate binding phase.

Transport competition between monovalent and divalent cations through cation-exchange membranes. Exchange isotherms and kinetic concepts

Separation of Ca 2+ or Cu 2+ ions from binary solutions with Na + or protons by electrotransport through strong cation-exchange membranes (CEM) has been studied in the case where no sorbed species is present within the membrane material. The study was achieved on two conventional CEM and two CEM manufactured to be preferentially permselective to monovalent cations. Without any applied driving force, the exchange isotherms exhibit no significant increase in permselectivity for the modified CEM. Divalent cations are preferred by the membranes due to their higher electrostatic attraction with the oppositely fixed charged exchange sites. When the CEM are submitted to an electrical field, radiotracer measurements exhibit the difference of permselectivity of these two types of CEM. The apparent rate constants of the ionic interfacial transfer were calculated on the basis of unidirectional fluxes and concentration profiles of cations within the unstirred layer. The values of these kinetic constants were always greater for monovalent than for divalent cations but the difference was more important for modified membranes. Lastly, comparison between the potential profiles showed that the potential decrease within the depleted unstirred layer was more important for the solutions less concentrated in protons.

Comparison of transport of alkali halides and nitrates across asymmetric cellulose acetate and polyamide, composite poly(etherurea), and cation exchange membranes

Using typical synthetic membranes (asymmetric CA and polyamide, composite poly (ether—urea), strong cation exchange membrane), hydrodynamic permeabilties, lp, normalized salt permeabilities, P s/d, and asymptotic rejections, r ∞, for alkali chlorides and nitrates as well as for sodium halides were obtained from hyperfiltration experiments with 0.01 m and partially with 0.2 m brine solutions. Using the measured transport parameters, partition coefficients, K s, and diffusion coefficients, D sm, within the membranes were estimated. In general, the partition coefficients of the asymmetric CA membranes for the alkali chlorides increase in the following order CsCl < RbCl < KCl ⋍ LiCl < NaCl whereas no such clear sequence exists with the alkali nitrates. On the other hand, the sequence is nearly reversed with the cation exchange membrane. The normalized salt permeabilities, P s/d (d = effective membrane thickness), of sodium salts increase in the order Cl − < NO 3 − < Br − < I − for all membranes except the CK—1 membrane which exhibits a reversed sequence. Moreover, varying the cation or anion, respectively, the normalized salt permeabilities of the CK—1 membrane vary according to Walden's rule Λ·η = const.·T (Λ = equivalent conductivity, η = viscosity, T = absolute temperature). It is tried to correlate the variations of the cation and anion partition coefficients, K s = K co = 1 — r ∞, as well as of the normalized permeabilities, P s/d, with the Gibbs free energy of hydration of the alkali ions, Δ G hy.

Speciation of Cadmium(II) Using Donnan Dialysis and Differential-Pulse Anodic Stripping Voltammetry in a Flow-Injection System

Abstract A flow-injection/Donnan dialysis/differential pulse anodic stripping voltammetry system was developed for the determination of free cadmium concentrations, [Cd2+], in solutions containing organically complexed Cd(II). A small dialysis cell with a strong cation-exchange membrane separating the sample and the receiver channels, was equilibrated in a flow-injection system. The ionic strength of sample and receiver solutions was 0.1 M, with NaNO3 as the bulk electrolyte. By determining a constant fraction of the Cd2+ associated with the membrane phase, [Cd2+] of the samples could be measured. Experimentally determined [Cd2+] corresponded well with those calculated, using tabulated stability constants, when citric acid, nitrilotriacetic acid, and oxalic acid were added as ligands. Thus, negatively charged and uncharged complexes were excluded from the membrane. Using the experimental design presented, [Cd2+]>5 × 10×8 M could be determined, but there is a great potential for increasing the sensitivity ...

Feasibility of separation of cations in electrodialysis in relation to concentration polarization

Separation of Cs +, Sr 2+ or La 3+ from binary solutions with Na + by electrodialysis through a strong cation-exchange membrane has been studied. The results are correlated with the concentration polarization behaviour of the membrane. Polarization curves were traced at a number of solution compositions and constant total concentrations of 0.01 and 0.05 M. Radiotracers were used to determine the separation coefficients of cations by electrodialysis, the selective uptake of cations by the membrane and the co-ion leak. The change in pH during electrodialysis was measured. Substitution of Na + by the cations of higher membrane affinity in mixtures deformed the polarization curves and raised the limiting current density in the order Cs +<La 3+<Sr 2+. The higher the valency and the lower the total concentration, the higher is the selective uptake of the preferred cations over Na +. Efficient cation separation is realized at low current densities independent of the solution composition. However, as the current density increases the efficiency decreases until Na + is preferentially transported. Concentration polarization is detrimental to the cation separation even at currents well below the limiting current density. In the presence of concentration polarization, the extent of co-ion leak is a function of the nature of cations, while the transport of hydrogen ions through the cationic membrane is negligibly small and cation independent.

Electric and electrokinetic transport properties of homogeneous weak ion exchange membranes

The effect of H + ions on the membrane potential and electrical resistance of synthetic membranes has been investigated theoretically and experimentally for salt solutions of typical pH values. Employing the equations of Schlögl for the membrane potential Δϕ and the specific electrical resistance ϱ, membrane potentials and resistances have been calculated for binary and ternary electrolyte solutions. Moreover, the effect of a dissociation equilibrium of the fixed charges (COOH groups) in the membrane on the membrane potential and resistance have been considered. The ratios of the mobilities of the cations and the anions have been estimated at relatively large external salt concentrations from membrane potential curves measured with LiCl-HCl, HCl, CaCl 2-HCl, Na 2SO 4-H 2SO 4, and MgSO 4-H 2SO 4 using weak cation exchange membranes such as homogeneous cellulose acetate, cuprophane, and carboxy methyl cellulose, as well as strong cation exchange membranes such as ASAHI's CK-1 and a Nation membrane. From measurements of the electrical resistance of homogeneous cellulose acetate membranes at different salt concentrations but prescribed pH values for the systems LiClHCl, MgCl 2HCl, and MgSO 4H 2SO 4, individual ion diffusion coefficients have been estimated. Further, the concentration dependence of the ion diffusion coefficients in the membrane has been demonstrated. The counterion diffusion coefficients exhibit a strong change of their diffusion coefficients ranging from 10 −14 up to 10 −9 cm 2/sec in the concentration range 10 −4 mole/liter < c s < 10 −1 mole/liter, whereas the coion diffusion coefficients and the H +-ion diffusion coefficient vary slightly with the external electrolyte concentration and are of the order of 10 −8 to 10 −7 cm 2/sec and 8 × 10 −7 to about 3 × 10 −6 cm 2/sec, respectively.