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PubMed2003

Selectivity behaviour of a bonded phosphonate--carboxylate polymeric ion exchanger for metal cations with varying eluent compositions.

The chromatographic behaviour of a commercially available ion-exchange stationary phase (the Dionex IonPac CS12A column) is described for a wide range of transition and heavy metal ions with nitric acid eluents containing chloride and nitrate potassium salts. The separation selectivity was found to arise from simultaneous ion-exchange interactions and chelation with the attached carboxylic and phosphonic acid groups. These interactions were investigated by altering the ionic strength and pH of the eluent and also the column temperature. Strong affinity of the stationary phase towards heavy metal ions, in particular bismuth and the uranyl ion was observed at low pH under chelating ion-exchange conditions, with high efficiency separations of other ions including cadmium and lead being possible with short analysis times (approximately 5-15 min). Examples are given of separations obtained using 4-(2-pyridylazo)resorcinol or Arsenazo III as the post-column chromogenic reagents, demonstrating the potential versatility and utility of this stationary phase for heavy metal ion analysis.

Carboxylic Acids↗

PubMed2006

Chromate (CrO(4)(2-)) and copper (Cu2+) adsorption by dual-functional ion exchange resins made from agricultural by-products.

Ion exchange resins commonly have a single functionality for either cations or anions. Resins that have a dual functionality for both cations and anions are uncommon. The objective of this study was to create dual-functional ion exchange resins derived from soybean hulls, sugarcane bagasse and corn stover. Dual-functional resins were prepared by two separate two-step processes. In the first two-step process, by-products were reacted with a solution of citric acid in order to impart additional negative charge, and then reacted with the cross-linking reagent dimethyloldihydroxyethylene urea (DMDHEU) and a quaternary amine (choline chloride) to add positive charge to the lignocellulosic material. In the second two-step process, the order of reaction was reversed, with positive charge added first, followed by the addition of negative charge. These combined reactions added both cationic and anionic character to the by-products as evidenced by the increased removal from solution of copper (Cu(2+)) cation and the chromate (CrO(4)(2-)) anion compared to unmodified by-products. The order of reaction appeared to slightly favor the functionality that was added last. That is, if negative charge was added last, the resulting resin sequestered more copper ion than a comparable resin where the negative charge was added first and vice-versa. Cu(2+) and CrO(4)(2-) were used as marker ions in a solution that contained both competing cations and anions. The dual-functional resins adsorbed as much as or more of the marker ions compared to commercial cation or anion exchange resins used for comparison. None of the commercial resins exhibited dual-functional properties to the same extent as the by-product-based resins.

Adsorption↗

PubMed2000

Ion Exchange of Divalent Cobalt and Iron with Na-Y Zeolite: Binary and Ternary Exchange Equilibria.

Divalent cobalt and iron removal from aqueous solutions by batch ion exchange with a synthetic Na-Y zeolite has been studied under competitive and noncompetitive conditions. The binary Co/Na and Fe/Na ion-exchange equilibrium isotherms, constructed at 291+/-2 K and a total solution positive charge concentration of 0.1 eq dm(-3), exhibited sigmoidal shapes that are attributed to an exchange site heterogeneity. The solution pH and the ratio of sorbate to sorbent are identified for which minimal imbibition of metal hydroxide and maintenance of zeolite structural integrity are ensured. An increase in Fe and Co concentration over the range 0.005-0.05 mol dm(-3) lowered the removal efficiency but the external Fe was preferred to the indigenous sodium over the entire concentration range; there was a switch in preference from Co to Na at [Co] in excess of 0.034 mol dm(-3). Exchange data for Cu(2+)/Na(+) and Ni(2+)/Na(+) binary systems are included for comparative purposes, and ion exchange affinity and Na-Y exchange capacity are discussed in terms of metal ion hydration and ion location. The effect of exchange temperature has been considered where the maximal Fe exchange was temperature independent while Co exchange was promoted with increasing temperature. A Co/Fe/Na-Y ternary exchange isotherm was constructed from 20 pairs of experimental points and is treated quantitatively in terms of ternary and pseudo-binary separation factors. The preference of the zeolite for exchange with iron over cobalt under noncompetitive conditions also extended to solutions containing both metals. Copyright 2000 Academic Press.

Journal Article↗

PubMed2004

Distribution of a bovine spongiform encephalopathy-derived agent over ion-exchange chromatography used in the preparation of concentrates of fibrinogen and factor VIII.

BACKGROUND AND OBJECTIVES: The risk of haemophiliacs contracting variant Creutzfeldt-Jakob disease (vCJD) via treatment with factor VIII concentrates is not known. Therefore, in order to determine the extent to which the vCJD agent might be removed during the preparation of factor VIII concentrate, the partitioning of a bovine spongiform encephalopathy (BSE)-derived agent was measured over the main purification step used to prepare the Scottish National Blood Transfusion Service high-purity factor VIII concentrate (Liberate). MATERIALS AND METHODS: Murine-passaged BSE (strain 301V), in the form of a microsomal fraction prepared from infected brain, was used to 'spike' a solution of factor VIII of intermediate purity. The 'spiked' starting material was subjected to solvent-detergent treatment and then to anion-exchange chromatography with Toyopearl DEAE-650M. All fractions were tested for 301V infectivity using a murine bioassay, including the procedures used to clean the ion-exchange media after use. RESULTS: BSE 301V infectivity was reduced by 2.9 log(10) in the fibrinogen fraction and by 2.7 log(10) in the factor VIII fraction. Over 99% of the added 301V infectivity remained bound to the ion-exchange column after elution of factor VIII. A large quantity of infectivity was subsequently removed by washing the ion-exchange media with 2 m NaCl. No further BSE 301V infectivity was detected in column eluates after treatment with 0.1 m NaOH or a second wash with 2 m NaCl. CONCLUSIONS: Results using a BSE-derived agent suggest that vCJD infectivity would be substantially removed by the ion-exchange process used in the preparation of fibrinogen and factor VIII concentrate. Although 301V infectivity remained bound to the ion-exchange matrix following elution of factor VIII, this appeared to be eliminated by the procedure used for cleaning the ion-exchange media after each use.

Adsorption↗

PubMed1988

Na+/H+ ion-exchange property of postmortem human gastric mucus.

The Na+/H+ ion-exchange property of human gastric mucus and its relationship to age has been studied. Mucus was collected from 40 postmortem human stomachs (age range, 21-83 years) within 24 h of traumatic death. Twenty-one stomachs (age range, 21-76 years) were free of Campylobacter pylori infection and histologic gastritis. Mucus from these stomachs was consistently a cation exchanger at pH 6 in an in vitro system. The cation-exchange capacity of mucus from seven stomachs within the age range 55-70 years was 50% less than the cation-exchange capacity of mucus from eight stomachs within the age range 20-35 years. This study shows that human gastric mucus at pH 6 is a cation exchanger and that the ion-exchange capacity decreases with age.

Adult↗

PubMed1990

New family of high-resolution ion exchangers for protein and nucleic acid purifications from laboratory to process scales.

A new family of polymer-based ion exchangers was tested for the purification of acidic and basic proteins on both the analytical and preparative scales. Protein-Pak HR series packings are available as strong cation (SP) and weak anion (DEAE) exchangers, allowing the development of a purification method regardless of the isoelectric point of protein. Three particle sizes, 8, 15 and 40 microns, are offered in scalable Advanced Purification (AP) glass columns or as bulk packings. The lower back pressures of the 15- and 40-microns packings compared to that of the 8-microns material allow rapid throughput of large volumes without exceeding the pressure limitations of the resin or the column. The capacity of the AP1 (100 mm x 10 mm) glass columns, containing these ion-exchange packings, is comparable to other ion-exchange columns. The resolution of mouse serum, plasmids, and a standard protein mixture was demonstrated and compared with the results obtained with other resin-based ion exchangers of similar particle size. Proteins were purified without significant loss of biological activity or mass.

Alkanesulfonates↗

PubMed2004

Highly sensitive determination of hydrazine ion by ion-exclusion chromatography with ion-exchange enhancement of conductivity detection.

An ion-exclusion chromatography method with ion-exchange enhancement of conductivity was developed for the selective separation and sensitive determination of hydrazine ion from alkali/alkaline earth metal cations and ammonium ion. Hydrazine ion was separated by ion-exclusion/penetration effect from other cations on a weakly basic anion-exchange column in the OH- form (TSKgel DEAE-5PW). Moreover, two different ion-exchange resin columns were inserted between the separating column and conductimetric detector in order to improve the sensitivity of hydrazine ion. The first enhancement column packed with a strongly basic anion-exchange resin in the SO4(2-) form (TSKgel SAX) for hydrazine ion can convert from N2H5OH to (N2H5)2SO4. Moreover, the second enhancement column packed with a strongly acidic cation-change resin in the H+ form (TSKgel SCX) can convert to H2SO4. As a result, the sensitivity of hydrazine ion using two conductivity enhancement columns could be 26.8-times greater than using the separating column alone. This method was effectiveness also for the enhancement of ammonium ion (6.1-times) and sodium ion (1.2-times). The calibration graph of hydrazine ion detected as H2SO4 was linear over the concentration range of 0.001-100 ppm (r2 = 0.9988). The detection limit of hydrazine ion in this system was 0.64 ppb. Therefore, hydrazine ion in real boiler water sample could be accurately determined, avoiding the interference of other cations.

Calibration↗

PubMed1953

[Ion exchangers].

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Ion Exchange↗

PubMed2006

Ion-exchange properties of cell walls of Spinacia oleracea L. roots under different environmental salt conditions.

Ion-exchange properties of the polymeric matrix of cell walls isolated from roots of 55-day-old Spinacia oleracea L. (Matador cv.) plants grown in nutrient solution in the presence of 0.5, 150, and 250 mM NaCl and from roots of Suaeda altissima L. Pall plants of the same age grown in the presence of 0.5 and 250 mM NaCl were studied. The ion-exchange capacity of the spinach cell walls was determined at pH values from 2 to 12 and different ionic strength of the solution (10 and 250 mM NaCl). In the structure of the root cell walls, four types of ionogenic groups were found: amine, two types of carboxyl (the first being galacturonic acid residue), and phenolic groups. The content of each type of group and their ionization constants were evaluated. The ion-exchange properties of spinach and the halophyte Suaeda altissima L. Pall were compared, and the qualitative composition of the ion-exchange groups in the cell walls of roots of these plants appeared to be the same and not depend on conditions of the root nutrition. The content of carboxyl groups of polygalacturonic acid changed in the cell walls of the glycophyte and halophyte depending on the salt concentration in the medium. These changes in the composition of functional groups of the cell wall polymers seemed to be a response of these plants to salt and were more pronounced in the halophyte. A sharp increase in the NaCl concentration in the medium caused a decrease in pH in the extracellular water space as a result of exchange reactions between sodium ions entering from the external solution and protons of carboxyl groups of the cell walls. The findings are discussed from the standpoint of involvement of root cell walls of different plant species in response to salinity.

Cell Wall↗

PubMed2000

Improved reliability of leucite reinforced glass by ion exchange.

OBJECTIVES: The aim of this study was to develop an adequate process-, proof- and calculation technique for the chemical strengthening of dental ceramic materials in order to evaluate the efficiency of this method from the engineering point of view. METHODS: Ion exchange examinations below glass temperature have been done for the dental all ceramic system IPS-Empress (Ivoclar). In addition experiments on specimens were undertaken, which were stored in artificial saliva for the period of one month after the ion exchange treatment. The efficiency of the ion-exchange treatments has been evaluated based on the chemical composition of the surface layer, the residual stress distribution, the flexural- and the burst-strength and surface hardness. In addition, Weibull statistical analysis of the four-point bending and burst test data provides new information about the failure mechanisms of chemically strengthened dental ceramics. RESULTS: The ion-exchange process with a potassium salt increases the reliability of the dental ceramic material "IPS-Empress". By the KNO3 or Tuf-Coat ion exchange treatment potassium ions will be implanted as clusters directly into the crystal lattice which results in an increase of the binding energy and hence, in a pronounced increase in the surface hardness. In particular the stress bearing capabilities of dental all ceramic restorations, which are subject to high bending stresses, i.e. dental crowns and dental bridges, are largely improved by the induced residual stresses. This increase of residual stresses did not relax significantly after a one month storage in artificial saliva. SIGNIFICANCE: Enhanced load limits and a more narrow strength distribution spectrum is considered desirable for increasing the clinical longevity of all ceramics.

Algorithms↗

PubMed1992

Strengthening of porcelain by ion exchange subsequent to thermal tempering.

The purpose of this study was to test the hypothesis that high-leucite content feldspathic porcelain can be strengthened best by thermal tempering followed by ion exchange, compared with either thermal tempering or ion exchange alone. The results of biaxial flexure testing indicate that thermal tempering was the most effective way of strengthening the porcelain among the three methods tested. The combined procedure did not yield the greatest strengthening effect as hypothesized, but one that is only slightly stronger than that produced by ion exchange alone. Weibull analysis indicated that the ion-exchange treatment resulted in a narrower distribution of biaxial flexural strength compared with that of untreated or thermally tempered porcelain. The narrower distribution of biaxial flexural strength is considered desirable for enhancing the longevity of ceramic-based dental restorations.

Dental Porcelain↗

PubMed2002

In situ remediation of groundwater contaminated by heavy- and transition-metal ions by selective ion-exchange methods.

Laboratory studies were conducted to investigate the feasibility of using ion-exchange resins in permeable reactive barriers (PRBs) for the remediation of groundwater contaminated by heavy and transition metals. Ion-exchange resins represent an essentially neglected class of materials which may, in addition to iron, activated carbon, and zeolites, prove effective for use in PRBs. Four resins were considered: two commercially available resins, Duolite GT-73 (Rohm and Haas) and Amberlite IRC-748 (Rohm and Haas), and two solvent-impregnated resins (SIRs). The SIRs were prepared from Amberlite IRA-96 (Rohm and Haas) and two different thiophosphoric extractants. All four resins are able to reduce cadmium, lead, and copper concentrations from 1000 microg/L (typical for contaminated groundwaters) to below 5 microg/L. Significantly, all of the resins are effective for the capture of cadmium, copper, and lead, even in the presence of CaCl2 and clay. Because of their high hydraulic conductivity, the use of these resins in clusters of wells, as an alternative to continuous walls, is considered in the design of effective PRBs. Numerical solution of the groundwater flow equations shows that, depending on the well configuration, most (or all) of the contaminated groundwater can pass through the resins. These results demonstrate the possibility of using selective ion-exchange resins as an effective, active material in PRBs for in situ groundwater remediation.

Ion Exchange↗

PubMed1987

High-performance liquid chromatographic separation of biological macromolecules on new silica-based ion exchangers.

The fundamental characteristics of a new series of ion-exchange columns, specifically designed for high-speed analysis of biological macromolecules, have been examined. Each of these columns is packed with a chemically modified silica gel, that has a controlled pore-size distribution and a uniform particle diameter. Surface silanol groups of these materials are chemically modified with hydrophilic polymers to produce a neutral silica surface, and ionic functional groups are chemically bonded to this neutral support, producing a stable ion exchanger. The separation of biological macromolecules on these columns has been investigated, and the selection of a mobile phase is discussed.

Chromatography, High Pressure Liquid↗

PubMed2005

Preparation of ion-exchange fiber fabrics by electrospray deposition.

Ion-exchange fiber (IEF) fabrics were prepared by electrospray deposition (ESD) and post-deposition chemical modification of their surfaces. Nonwoven fibrous fabrics were obtained from the solutions of synthetic polymers-polystyrene (PS) and poly(4-vinylpyridine) (P4VP)-of various concentrations. The diameter of the fiber in the fabrics ranged from 600 nm to 1.70 microm. Cation- and anion-exchange fiber (CEF and AEF) fabrics were obtained from the sulfonation of PS fabrics and the quaternization of P4VP fabrics, respectively. These fabrics were thoroughly characterized by a series of techniques, such as scanning electron microscopy (SEM), permporometry, nitrogen adsorption measurements, and potentiometric titrations. The SEM images showed that the fabrics had a porous structure after their chemical modification. The mean pore size, porosity, and specific surface area of the flow-through pores were 1.67-3.53 microm, about 80%, and 13 m(2)/g, respectively. The ion-exchange capacity was in the range from 0.78 to 1.34 mmol/g. The AEF fabric, on the other hand, showed a high specific surface area, i.e., the Brunauer-Emmett-Teller (BET) surface area of 600 m(2)/g, due to the formation of much smaller pores on the surface of the fiber structure in the fabric. The secondary chemical modification of the nano-microfiber fabrics by ESD provides novel functional materials with a large adsorption capacity and a high catalytic activity.

Journal Article↗

PubMed2006

Systematic modeling study of channel waveguide fabrication by thermal silver ion exchange.

A systematic study of thermal silver ion exchange used for the fabrication of optical channel waveguides is reported in a single-alkali glass. The diffusion equilibrium and diffusion dynamics are experimentally studied, and the concentration-dependent diffusion coefficients are determined. The relationship between the fabrication conditions, i.e., time, temperature, and melt concentration, and the induced waveguide refractive index profile is established. It is demonstrated that the diffusion equation can be solved, without use of any free parameters, to predict the refractive index profiles of both planar and channel waveguides. A 1.6 cm diameter integrated optic ring resonator, with a propagation loss of 0.1 dB/cm, is fabricated in a glass by thermal silver ion exchange. The induced refractive index profile is related to the optical characteristics of the functional device.

Journal Article↗

PubMed2002

High-throughput screening and quantitative structure-efficacy relationship models of potential displacer molecules for ion-exchange systems.

A technique is presented for the high-throughput screening of ion-exchange displacers. Potential displacers were employed to displace proteins in parallel batch ion-exchange experiments. The percentage of protein displaced from a particular stationary phase was then used as a parameter to rank the displacers. By employing this technique, a large number of molecules possessing a range of affinities and properties could be rapidly evaluated. This data was then used together with traditional and electron density-based transferable atom equivalent (TAE) molecular descriptors computed for the displacer molecules to produce quantitative structure-efficacy relationship (QSER) models using a genetic algorithm/partial least squares (GA/PLS) regression approach. The QSER models were generated using a portion of the protein-displacement data, with the remainder serving as a test set. Descriptor selection and model building was accomplished using a genetic algorithm/partial least squares approach. The resulting models were found to have high-correlation coefficients and could be used to accurately predict the behavior of molecules not included in the training set. In addition, the models were employed to examine a virtual library of displacers based on modifications of neomycin to provide further insight into displacer design. The results presented here indicate that it may be possible to design displacers that can dramatically improve the effective selectivity of ion-exchange chromatographic materials.

Algorithms↗

PubMed1998

Retention behaviours and separation of carboxylic acids by ion-exchange chromatography.

The use of high-performance suppressed ion chromatography for the separation of aliphatic carboxylic acids has become an attractive and viable method during the past years. This paper summarises and critically concludes that some new results have been achieved in separation and detection of low-molecular-mass organic anions. Theoretical and practical considerations of ion-exchange selectivity to control retention behaviour are presented. The major factors that determine the separation ability of ion-exchange chromatography (pKa values, the aliphatic nature and valency of solutes, eluent pH and the chemical composition of stationary phases) are discussed. The question of isocratic vs. gradient elution and different separation modes are examined briefly. The potentials and limitations of the developed methods and their specific application areas are outlined.

Carboxylic Acids↗

PubMed2002

Ion-exchange funneling in thin-film coating modification of heterogeneous electrodialysis membranes.

Inexpensive highly permselective heterogeneous ion-exchange membranes are prohibitively highly polarizable by a dc current for being used in electrodialysis. According to recent experiments, polarizability of these membranes may be considerably reduced by casting on their surface a thin layer of crosslinked polyelectrolyte, slightly charged with the same sign as the membrane's charge. The present paper is concerned with this effect. Concentration polarization of a permselective heterogeneous ion-exchange membrane by a dc current is determined by geometric factors, such as, the typical size of the ion-permeable "gates" at the membrane surface relative to the separation distance between them and the diffusion layer thickness. The main quantitative characteristic of polarizability of a heterogeneous membrane is its voltage/current curve with its typical saturation at the limiting current, which is lower than that for a homogeneous membrane. In the present study we modify the previously developed two-dimensional model of ionic transport in a diffusion layer at a heterogeneous ion-exchange membrane by including into consideration a homogeneous ion-exchange layer adjacent to the membrane surface. A numerical solution of the respective boundary value problem shows that, indeed, adding even a very thin and weakly charged layer of this kind increases the value of the limiting current, to that of a homogeneous membrane. What differs, for different values of coating parameters, is the form of the voltage/current curves but not the value of the limiting current, namely: the thinner is the coating and the lower the fixed charge density in it, the "slower" is the approach of the limiting current. In order to explain this feature, a simple limiting model of modified membrane is derived from the original two-layer model. In this limiting model, asymptotically valid for a thin coating, solution of the ionic transport equations in it is replaced, via a suitable averaging procedure, by a single nonlinear boundary condition for the membrane/solution interface. Rigorous analysis shows that the aforementioned property of the limiting current is an exact mathematical feature of this limiting model, when the underlying physical phenomenon is the funneling of counterions by the charged layer from the impermeable parts of the membrane towards the "entrance gates." An approximate analytical solution, developed for this model, compares well with the exact numerical one.

Journal Article↗