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The effect of the conditions of preparation of cation-exchange resins on their resolution efficiency in ion-exchange chromatography of amino acids.
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Fractionation of DNA restriction fragments with ion-exchangers for high-performance liquid chromatography.
The fractionation abilities of several ion-exchangers of the high-performance liquid chromatography type for two sets of DNA restriction fragments, ranging from 7 base pairs (bp) to about 650 bp and differing in their mean base composition, have been studied. The ion-exchangers tested comprise the RPC-5, the 5-PW DEAE and the Mono Q as polymer-based resins, and the Nucleogens 500 and 4000, both prepared from silica beads. The results indicate that all the ion-exchangers except the 5-PW DEAE perfectly separate fragment sizes up to about 90 bp, the 5-PW DEAE separating to 45 bp only. Above 200 bp only the Mono Q resin works in a satisfactory way provided that about 100 micrograms DNA mixture, containing less than 25 fragments within the given size range, is loaded per milliliter of packed resin. Appreciable base-pair specificities were detected for most of the resins which cause substantial retardations of the d(A + T)-rich fragments with respect to the eluting salt concentration. If the latter dominate in the DNA sample, acceptable results were only obtained with the Mono Q resin when the column was operated at elevated temperature.
Influence of hydrophobicity on the ion exchange selectivity coefficients for aromatic amines.
Hydrophobic effects could play an important role in determining the selectivity of organic ions for ion-exchange resins in aqueous solutions. We used the octanol-water partition coefficient (P) and the chromatographic capacity factor (K') as indices of hydrophobicity of a series of primary and secondary amines, and examined their relationships with the amine selectivity coefficient (K) in binding to the Amberlite IRP-69 ion-exchange resin. Good correlations were found between log K versus log P and log K versus log K', but the relationship appears to be dependent on the degree of substitution at the amino nitrogen. These relationships may be useful for the estimation of selectivity coefficients of various amine drug candidates when they are considered for incorporation with ion-exchange resins in potential controlled-release systems.
Magnetic Effect on Ion-Exchange Kinetics.
Effects of magnetic exposure on an ion-exchange process are investigated, employing ion-exchange resins. The electrolyte solution, resin suspension, and water are mixed in a container, and the mass transfer coefficient is determined by measuring the change of the ionic concentration in the bulk. Two methods of magnetic exposure are performed: case (1) in which only the electrolyte solution is exposed to the magnetic field and case (2) in which only the resin suspension is exposed to the magnetic field. The following features are found in both cases: (i) the film mass transfer rate reduces by about 5% when the exposure time is greater than 25 min, (ii) the magnetic effect is reduced by adding the alcohol, (iii) the magnetic effect remains for about 3 days but disappears after 6 days, and (iv) the magnetic effect is observable in the solutions of structure-disordering ions, but not in the solutions of structure-ordering ions. As for the temperature dependence, the magnetic effect decreases with temperature in case (1) but it stays constant in case (2). It is postulated that the magnetic effects are attributable to the stabilization of water molecules around the structure-ordering ion and those on the resin surface. Copyright 1999 Academic Press.
Ion-exchange-based eluent-free preconcentration of some anions.
Preconcentration procedures based on ion-exchange methods are often used to enhance the sensitivities of analytical techniques where the eluent used for eluting the preconcentrated ions does not influence the subsequent analytical step. Until recently, only a limited use of ion-exchange-based sample preconcentration procedures has been found in those analytical techniques where the eluent components strongly influence the separation procedure [e.g., capillary electrophoresis (CE)]. In this paper, we present a preconcentration procedure based on (i) the preconcentration of anions on an ion-exchange resin, (ii) the subsequent elution of analytes, and (iii) on-line removal of eluent components by chemical suppression using an appropriate suppressor device (either packed-bed suppressor column or micromembrane suppressor). The adjustment of the system parameters, combined with a computer-controlled, sensing/switching system, resulted in a minimal additional dilution of the eluted preconcentrated anions. The efficiency of the proposed enrichment/matrix removal procedure was tested by using off-line CE analysis of collected preconcentrated samples, reaching a LOD of 1 microg/l for a selected anion.
[Research on an ionexchange model for knowledge on the physiology of biogenic amines. Exchange equilibrium between sodium and amines on an ion-exchanger with R-PO(OH)2 as the active centers].
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Ion exchange of Pb(2+), Cu(2+), Fe(3+), and Cr(3+) on natural clinoptilolite: selectivity determination and influence of acidity on metal uptake.
In the present study ion exchange of Pb(2+), Cu(2+), Fe(3+), and Cr(3+) on natural Greek clinoptilolite was examined in terms of selectivity toward the above heavy metals in single- and multicomponent solutions in batch systems. Also examined are the influence of clinoptilolite on solution acidity and the effect of acidity on the ion exchange process. Clinoptilolite increases solution acidity due to the exchange of H(+) cations with the cations initially present in its structure. H(+) cations should be considered as competitive ones in ion exchange processes, and consequently ion exchange of metals is favored at high acidity values. Cu(2+) and Cr(3+) are the most sensitive cations with respect to acidity. Selectivity determination demonstrates that the selectivity at total concentration 0.01 N and acidity 2 in both single- and multicomponent solutions is following the order Pb(2+)>Fe(3+)>Cr(3+) > or =Cu(2+). This order is set since the first days of equilibration. However, Cu(2+) shows remarkable changes in selectivity and generally its uptake and selectivity are increasing with time. On the other hand selectivity in single metal solutions where acidity is not adjusted is following the order Pb(2+)>Cr(3+)>Fe(3+) congruent with Cu(2+).
Equilibrium and dynamic investigations of organic acids adsorption onto ion-exchange resins.
The aim of the study was to determine properties of selected ion-exchange resins for citric and lactic acids recovery, to define sorption isotherms for these acids at different temperatures (in the range of 20-60 degrees C) and to determine diffusion coefficients inside sorbent particles. A mathematical model of the ion-exchange process in the chromatographic column and its experimental verification is also presented. During investigations 18 types of ion-exchange resins were tested. It was found that weakly basic resins were more suitable for the recovery process than strongly basic ones. The best resin for the separation of citric acid was Amberlite IRA-67 and for lactic acid Amberlite IRA-92. As a result of transient-state sorption experiments diffusion coefficients of the citric acid inside the sorbent particle at different temperatures were obtained. It was found that D(p) increased with the temperature by two times in the range of 20-60 degrees C, and its value at 60 degrees C was 7.2 x 10(-10) m(2)/s. The proposed mathematical model was applied to identify bed operation parameters in the column for the needs of the simulated moving bed chromatography method.
Comparison between a microdiffusion and an ion exchange method for the determination of plasma ammonium.
The results of plasma-ammonium determinations by an ion-exchange method and by a microdiffusion method were compared on the same specimens with each other and with ammonium determinations carried out on the corresponding whole-blood specimens by the microdiffusion method. The plasma-ammonium levels of whole-blood specimens were higher than those of the corresponding plasma specimens, but the difference was not constant. Recoveries of added NH(4) from plasma by the microdiffusion method ranged from 65 to 144%. Recoveries of NH(4) from the same specimens by the ion-exchange method ranged from 93 to 96%. Of the two, the ion-exchange method was the only one of value.
Effect of ion exchange resins on the drug release from matrix tablets.
Ion exchange resins were incorporated into hydroxypropylmethylcellulose (HPMC) matrix tablets to modify the release of oppositely charged drugs. The drug release from HPMC tablets containing drug-resin complexes was significantly slower than from HPMC tablets containing drug without resin. A physical mixture of drug and ion exchange resin (cationic drug, propranolol HCl, with the cation exchange resin, Amberlite IRP 69, or the anionic drug, sodium diclofenac, with the anion exchange resin, cholestyramine (Duolite ATP-143)) resulted in almost the same drug release as tablets containing preformed drug-resin complexes. Upon contact with the dissolution medium, a gel layer formed rapidly around the solid tablet core and the complex between the drug and the resin formed in situ within the gelled regions. No effect of pH of the dissolution medium (0.1 N HCl or pH 7.4 phosphate buffer) or resin counterion was observed with the strong cation exchanger, Amberlite IRP 69. The resin was dissociated at both pH-values, allowing drug binding. With the weak cation exchange resin, Amberlite IRP 88, in situ complex formation and retardation was only observed in pH 7.4 buffer but not in 0.1 N HCl because of the non-ionization of the carboxyl groups. The drug release depended also on the amount and particle size of the resin particles and the type of carrier. The use of smaller resin particles eliminated the burst release seen with larger resin particles. Upon comparing different carrier materials, a rapid formation of the gel layer was important for the in situ complex formation. The drug release was in the order of Gelucire 54/02 (glyceryl palmitostearate) > polyethylene oxide 400K > HPMC K15M.
Polyamines and Pectins (I. Ion Exchange and Selectivity).
The ion-binding and -exchange properties of putrescine, spermidine, and spermine on purified walls of carrot (Daucus carota L.) cell suspensions were investigated by producing ion-exchange isotherms and comparing them with the behavior of Na+, Mg2+, and Ca2+. The cation exchange capacity of the carrot cell walls was 0.8 equivalent kg-1 dry matter, and the ionic selectivity sequence of the walls for polyamines followed the sequence spermine4+ > spermidine3+ [almost equal to] Ca2+ > putrescine2+. The polyamines were subjected to only electroselectivity and probably did not induce any favorable supramolecular conformation of pectin like the one induced by Ca2+. Triangular ion exchanges were also performed with three diamines: ethanediamine, butanediamine, and octanediamine. The shorter the diamine, the higher the total adsorption and selectivity of the exchange. The lower selectivity of the cell wall for putrescine was partly attributed to its inability to access and displace Ca2+ from higher affinity sites within dimerized pectic sequences. The polyamine adsorption and exchange on pectic sequences could result in pectic signal modulation in pathogenesis and in differentiation.
Protein adsorption on novel acrylamido-based polymeric ion-exchangers. I. Morphology and equilibrium adsorption.
The protein uptake equilibrium and particle morphology are determined for novel polymeric ion-exchange media based on acrylamido monomers with a high density of functional groups and a variety of morphological characteristics. The study considers two anion-exchangers and a cation-exchanger. Physical properties determined experimentally include particle density, ion-exchange capacity, particle size distribution, and equilibrium isotherms for model proteins. The pore structure was evaluated using size exclusion chromatography with neutral probe molecules and transmission electron microscopy. For the anion-exchangers, two types of structures were inferred. The first is comprised of particles that contain a low-density gel supported by denser polymer aggregates. This material had a very low size-exclusion limit for neutral probes, but exhibited an extremely high and reversible protein adsorption capacity (280-290 mg BSA/ml). The second structure is comprised of particles with large, open macropores. While the size-exclusion limit was very high, the protein adsorption capacity was low (60 mg BSA/ml). Moreover, the adsorption was nearly irreversible. The physical structure of the cation-exchanger appeared to be intermediate between those of the anion-exchangers, containing both large pores and smaller pores yielding an intermediate, but reversible, protein uptake capacity (120-130 mg alphaCHY/ml). The different behavior of these materials with regards to protein adsorption correlates well with their physical structure. For these ion-exchangers, high protein adsorption capacities are attained when a low-density polymer gel with a high concentration of functional groups is present.
II. The simultaneous measurement of exchangeable body sodium and potassium utilizing ion exchange chromatography.
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Electrically facilitated molecular transport. Analysis of the relative contributions of diffusion, migration, and electroosmosis to solute transport in an ion-exchange membrane.
Electrically facilitated molecular transport in an ion-exchange membrane (Nafion, 1100 equiv wt) has been studied using a scanning electrochemical microscope. The transport rates of ferrocenylmethyltrimethylammonium (a cation), acetaminophen (a neutral molecule), and ascorbate (an anion) through approximately 120-micron-thick membranes were measured as a function of the iontophoretic current passed across the membrane (-1.0 to +1.0 A/cm2). Transport rates were analyzed by employing the Nernst-Planck equation, modified to account for electric field-driven convective transport. Excellent agreement between experimental and theoretical values of the molecular flux was obtained using a single fitting parameter for each molecule (electroosmotic drag coefficient). The electroosmotic velocity of the neutral molecule, acetaminophen, was shown to be a factor of approximately 500 larger than that of the cation ferrocenylmethyltrimethylammonium, a consequence of the electrostatic interaction of the cation with the negatively charged pore walls of the ion-exchange membrane. Electroosmotic transport of ascorbate occurred at a negligible rate due to repulsion of the anion by the cation-selective membrane. These results suggest that electroosmotic velocities of solute molecules are determined by specific chemical interactions of the permeant and membrane and may be very different from the average solution velocity. The efficiency of electroosmotic transport was also shown to be a function of the membrane thickness, in addition to membrane/solute interactions.
Operational properties of an inverted matrix cellulose CM ion-exchanger.
Productive CM is a recently available carboxymethyl ion-exchanger based on cellulose supplied by BPS Separation. It is supplied in an 'inverted matrix' form as a coherent structure with large voids and about 90% free volume. This paper reports mainly on the physical properties and robustness under normal use conditions using lysozyme as a model protein. The structure is shown by electron microscopy to be formed of fibrous or sheet material around macropores of around 100 microns in diameter. The material around the macropores is itself porous down to the smallest pores visible at perhaps 50 nm. The capacity under static and dynamic conditions was measured and found in both cases to be only slightly dependent on applied flow velocities up to 8 m h-1. The high porosity allowed cider fermentation broth and diluted egg white to be applied directly to a column without blockage and at a moderate pressure drop yet with a high superficial velocity. Compression of the bed at high flow rates did not occur at free space velocities up to 17 m h-1 with water and slightly lower with other fluids. The adsorption isotherm was determined and found to follow a Langmuir form. It proved to be totally stable to immersion in 1 M NaOH and 1 M NaCl without any measurable volume changes. Many of the properties were compared with those of other ion-exchange resins and found to be equivalent in capacity but superior in terms of stability, sustainable flow rates and dynamic capacity. It is concluded that the stability, performance under high flow rates and good capacity make it eminently suitable for use in large scale applications.
Models for biological ion exchangers. I. Proton magnetic resonance studies of water structure in Bio-Rex 70.
Bio-Rex 70, a carboxylic acid cation exchanger, is studied as a biological ion-exchanger resin model for cellular cytoplasm. High-resolution proton magnetic resonance spectra of 1l ionic forms of Bio-Rex 70 are determined. From measured cation exchange capacities, water contents, and chemical shifts for the resin-phase water protons, the dependence of the chemical shift on the counter ion is calculated. The observed chemical shifts (Hz/geq/kg internal water, referred to the Ba2+ form) for each ionic form are: H+, --0.5; Li+, --0.2; Na+, 1.2; K+, 2; Rb+, 2.1; Ag+, --0.4; NH4+, --2.0; NMe4+, 1.2; NEt4+, 1.8; Mg2+, --2.0; Ca2+, --1.5; Sr2+, --0.6; Ba2+, 0.0 Zn2+, --2.3; Cd2+, --4.7; and La3+, --3.3. The results are in good agreement with earlier studies on Dowex 50, indicating that the carboxylate ion exchanger behaves like a concentrated polyelectrolyte. The widths at half-height for the internal water peaks of the polyvalent forms are quite large, ranging from 40 to 100 Hz.
Effect of ion-exchange treatment on mechanical properties of new dental ceramics.
PURPOSE: To examine whether the ion exchange strengthening can be achieved for several new ceramics such as glass ceramics or castable ceramics. METHODS: The ceramics selected for this study were three porcelains and three castable ceramics. 60 bend bars of the respective ceramics (1 x 5 x 10 mm) were fabricated according to the respective manufacturer's directions. Finally, the respective specimens were polished up to 0.1 microm and then divided into two groups: one was coated with an ion-exchange paste and the other was not treated as the control. Then, for the respective ceramics the hardness, flexural strength and fracture toughness were investigated and compared to the control. RESULTS: Although the ion-exchange treatment significantly (P < 0.05, Scheffé's test) increased flexural strength and fracture toughness for the porcelain based ceramics, it did not increase these properties for the castable ceramics. The chemical treatment did not affect hardness for any of the specimens.