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PubMed2006

A comparative study of ion exchange kinetics in zinc/lead-modified zeolite-clinoptilolite systems.

The kinetics of zinc and lead ions removal by modified zeolite-clinoptilolite has been investigated. The rate of the ion exchange process for lead ions is faster than for zinc ions, as well as the time needed to reach the equilibrium. The ion exchange capacity of zeolite of lead ions is doubly higher than that of zinc ions. Diffusion models according to the Vermeulen's approximation, the parabolic diffusion model and the homogeneous diffusion model have been tested with the experimental data of ion exchange for zinc and lead. For both systems examined, the best fit of the models proposed with the experimental data was shown by the Vermeulen's approximation and the homogeneous diffusion model with t-->t(infinity). The diffusion coefficients are calculated from kinetic models of lead ions they are of the order of 10(-6)cm(2)/min, constant for all examined initial concentrations and not dependent on time. The diffusion coefficients in the system of zinc ions is of the order of 10(-8)cm(2)/min, also independent of initial concentrations, but decreasing with time from the beginning of ion exchange to the equilibrium.

Algorithms↗
PubMed2005

Determination of methenamine, methenamine mandelate and methenamine hippurate in pharmaceutical preparations using ion-exchange HPLC.

An ion-exchange column high-performance liquid chromatography (HPLC) method has been developed for the determination of methenamine in methenamine and methenamine hippurate pharmaceutical preparations. The HPLC method uses a Zorbax SCX-300 column with acetonitrile-0.1M sodium perchlorate monohydrate (pH 5.8) (70:30, v/v) as the mobile phase at the flow rate of 1 mL/min. UV-detection was at 212 nm. The linear concentration plots for methenamine were linear over the concentration range of 0.25-50mM for methenamine and methenamine mandelate standards. The intra-day RSD precision was <1.25%, and for inter-day, <1.85%. The peaks for mandelic acid, hippuric acid and the other ingredients from placebo tablets do not interfere with the analysis for methenamine. The accuracy of this method was shown to be 99-101% by measuring the recovery of methenamine from spiked placebo tablets. The assay of methenamine from methenamine hippurate tablets and from a urinary antiseptic tablet containing methenamine were in the range of 98-102%. This HPLC method is a fast, simple and straightforward method for the analysis of methenamine in pharmaceutical preparations.

Anti-Infective Agents, Urinary↗
PubMed1982

Ion-exchange high-performance liquid-chromatography steps in peptide purifications.

Ion-exchange high-performance liquid chromatography (HPLC; on Ultropac TSK DEAE and CM) is compared with conventional soft-gel ion-exchange chromatography in identical peptide purifications. The results show that separating properties are similar, but as expected, ion-exchange HPLC has a much higher resolving capacity and a higher sensitivity, and allows a considerably shorter total separation time. The same buffer systems as for conventional ion-exchange chromatography can be used, including urea to solubilize large peptides, if care is taken not to exceed the pH limits set by the column matrix. A complete purification scheme by HPLC in the nanomolar range, utilizing exclusion, ion-exchange, and reverse-phase chromatographies, is given with a complex peptide mixture from a digest of a large protein. Similar steps as in conventional soft-gel schemes can be utilized. It is concluded that ion-exchange HPLC is a suitable complement to commonly used reverse-phase HPLC steps and that it permits high speed and sensitivity over wide ranges of peptide sizes and amounts.

Aldehyde Dehydrogenase↗
PubMed1989

Ion-exchange equilibria of lysozyme, myoglobin and bovine serum albumin. Effective valence and exchanger capacity.

A series of ion-exchange equilibrium experiments were completed and analyzed by a mass action model. The isotherms at various counter-ion concentrations are regressed to determine the average number of binding sites, Z, the mass action constant, K, and the effective capacity of the exchanger, Pm. The estimates for Pm are 1-10 mmol of protein adsorbed per liter of packed Sepharose exchanger, in agreement with values determined from fitting the Langmuir isotherms. A geometric model, developed to relate the charge distribution of the exchanger and the size of the protein to the protein capacity, also confirms the estimates of Pm. The Z values estimated (and confirmed with an independent slope method) range from 0.8 to 3.6, indicating that most of the ionized sites on the protein do not undergo ion exchange. Geometric model estimates of exchanger sites covered by a protein at maximum surface coverage show that only 1-32% of the sites actually undergo ion exchange. This result indicates that adsorbed protein molecules "block" many exchanger sites, preventing other molecules from ion exchanging at those sites. This high degree of blocking by proteins also indicates that there is an excess of exchanger sites, as evidenced by Z showing no dependence on charge separation distance over the range 6-10 A. Scatchard pots of the equilibrium data indicate that there is competition between at least two different binding forms of each protein studied. For the high-affinity systems, cooperative binding was observed at low exchanger loading; the character then changed to heterogeneous competitive binding as the exchanger loading increased. The effect on an isotherm plot is a subtle but systematic deviation from the Langmuir and mass action models. More important, the competition means that Z represents an average for competing binding forms and, as such, Z can be fractional.

Chromatography, Ion Exchange↗
PubMed1977

Improvement of the efficiency of ion-exchange cellulose columns and their application.

Packing procedures and operating conditions for microparticulate ion-exchange cellulose columns were investigated. The efficiencies of ion-exchange cellulose and mixed-bed ion-exchange cellulose columns were compared. The mixed-bed columns contained ion-exchange cellulose and diatomite, and those with a 5:1 volume ratio of ion-exchange cellulose (average particle size 7 micronm) and diatomite were found to be superior in almost every respect. Medical, pharmaceutical, biochemical and environmental applications of this type of column are shown.

Cellulose↗
PubMed2002

[Removal of arsenate by a new type of ion exchange fiber].

A new type of ion exchange fiber was prepared for the removal of arsenate from water. A batch sorption experiments showed that the fibrous sorbent had high sorption capacity and good kinetic property for arsenate ion. The sorption kinetic data can be described by the Lagergren pseudo-second order rate equation very well. Freundlich model can simulate the adsorption equilibrium data of arsenate ion in the studied concentration range. The removal of arsenate by the fiber reached a maximum in pH value range of 3.5 to 7.0. The column performance was carried to assess the applicability of the ion exchange fiber for the removal of arsenate ion with satisfactory result. The diluted NaOH solution is an efficient eluant for the desorption of arsenate on from the fiber column, and 30 mL of 0.5 mol/L NaOH can quantitatively recover arsenate from water.

Adsorption↗
PubMed1983

Mobile phase selection for the high-performance ion-exchange chromatography of proteins.

Proper mobile phase selection significantly improved high-performance ion-exchange fractionations of proteins. The pH and salt content of the eluant affected chromatographic behavior on both strong and weak ion-exchange columns. The retention and resolution of a number of proteins was examined on strong and weak ion-exchange supports with regard to these mobile phase variables. The strong ion-exchange columns were found to be superior for the protein separations performed in this study. The selectivity of both weak and strong ion-exchange columns was pH dependent, however, strong ion-exchange columns were operable over a broader range of pH. Examination of the effect of salts demonstrated that their "displacing activity" could be divided into three categories: weak, intermediate, and strong with regard to the protein mixture utilized. Intermediate salts provided best resolution along with good recoveries. Strong displacing salts were useful for eluting strongly retained proteins. The selection of a mobile phase with respect to protein retention is discussed.

Chromatography, Ion Exchange↗
PubMed1981

Sustained-release drug delivery system I: Coated ion-exchange resin system for phenylpropanolamine and other drugs.

Ion-exchange resin-drug complexes have been used to formulate sustained-release products of acidic and basic drugs. However, sustained release may be difficult to achieve due to many variables. A novel technique is reported that minimizes these variables by providing a polymeric film coating to the ion-exchange resin-drug complex particles, making drug release from these particles diffusion controlled. Direct application of an atomized polymer solution to the fluidized ion-exchange resin-drug complex particles was ineffective in controlling drug release since the coating came off in the dissolution medium due to swelling and fracturing of the particles. Pretreatment of the ion-exchange resin-drug complex particles with an agent such as polyethylene glycol was essential for the particles to retain their geometry and coating during dissolution. With divinylbenzenesulfonic acid resin complexed with phenylpropanolamine as a model, mixtures of ethylcellulose-coated and uncoated resin-drug complex particles were prepared. These mixtures gave varying drug release profiles that showed rank-order correlation with plasma concentration profiles obtained in bioavailability studies with suspension dosage forms.

Biological Availability↗
PubMed2001

Ion-exchange fibers and drugs: an equilibrium study.

The purpose of this study was to investigate the mechanisms of drug binding into and drug release from cation-exchange fibers in vitro under equilibrium conditions. Ion-exchange groups of the fibers were weakly drug binding carboxylic acid groups (-COOH), strongly drug binding sulphonic acid groups (-SO(3)H), or combinations thereof. Parameters determining the drug absorption and drug release properties of the fibers were: (i) the lipophilicity of the drug (tacrine and propranolol are lipophilic compounds, nadolol is a relatively hydrophilic molecule), (ii) the ion-exchange capacity of the fibers, which was increased by activating the cation-exchange groups with NaOH, (iii) the ionic strength of the extracting salt (NaCl), which was studied in a range of 1.5 mM to 1.5 M, and finally (iv) the effect of divalent calcium ions (CaCl(2)) on the release of the model drugs, which was tested and compared to monovalent sodium ions (NaCl), and combinations thereof. It was found that the lipophilic drugs, tacrine and propranolol, were retained in the fibers more strongly and for longer than the more hydrophilic nadolol. The more hydrophilic nadolol was released to a greater extent from the fibers containing strong ion-exchange groups (-SO(3)H), whereas the lipophilic drugs were attached more strongly to strong ion-exchange groups and released more easily from the weak (-COOH) ion-exchange groups. The salt concentration and the choice of the salt also had an effect: at lower NaCl concentrations more drug was released as a result of the influence of both electrostatic and volume effects (equimolar drug:salt ratio). Incorporation of CaCl(2) in the bathing solution increased drug release considerably as compared to NaCl alone. The equilibrium distribution of the drug species between the fiber and external solution phases was also simulated and it was found that the theoretical modelling proposed describes adequately the basic trends of the behavior of these systems.

Calcium↗
PubMed2003

Ion-exchange fibers and drugs: a transient study.

The objective of this study was to theoretically model and experimentally measure the kinetics and extent of drug release from different ion-exchange materials using an in-house-designed flow-cell. Ion-exchange fibers (staple fibers and fiber cloth) were compared with commercially available ion-exchange materials (resins and gels). The functional ion-exchange groups in all the materials were weak -COOH or strong -SO3H groups. The rate and extent of drug release from the fibers (staple fiber>fiber cloth) was much higher than that from the resin or the gel. An increase in the hydrophilicity of the model drugs resulted in markedly higher rates of drug release from the fibers (nadolol>metoprolol>propranolol>tacrine). Theoretical modelling of the kinetics of ion exchange provided satisfactory explanations for the experimental observations: firstly, a change in the equilibrium constant of the ion-exchange reaction depending on the drug and the ion-exchange material and, secondly, a decrease in the Peclet number (Pe) with decreasing flow-rate of the drug-releasing salt solution.

Ion Exchange↗
PubMed2006

An exclusion mechanism in ion exchange chromatography.

Protein dynamic binding capacities on ion exchange resins are typically expected to decrease with increasing conductivity and decreasing protein charge. There are, however, conditions where capacity increases with increasing conductivity and decreasing protein charge. Capacity measurements on two different commercial ion exchange resins with three different monoclonal antibodies at various pH and conductivities exhibited two domains. In the first domain, the capacity unexpectedly increased with increasing conductivity and decreasing protein charge. The second domain exhibited traditional behavior. A mechanism to explain the first domain is postulated; proteins initially bind to the outer pore regions and electrostatically hinder subsequent protein transport. Such a mechanism is supported by protein capacity and confocal microscopy studies whose results suggest how knowledge of the two types of IEX behavior can be leveraged in optimizing resins and processes.

Antibodies, Monoclonal↗
PubMed2004

Ion-exchange selectivity of anion exchange resin modified with polystyrenesulfonic acid.

In order to change the ion-exchange selectivity of anion-exchange resin, the surface of a gel-type anion exchange resin was modified with anionic polyelectrolyte, polystyrenesulfonic acid. Using this modified resin, the ion-exchange rate of nitrate was little decreased, but that of sulfate was evidently decreased. It is considered that the ion-exchange reaction of the multivalent anion is suppressed by the greater electrostatic repulsive force against the modification layer than that against the monovalent anion. Thus, this modified resin may be suitable for the selective separation of monovalent anions. The influence of the modified condition on the ion-exchange rate was examined. Furthermore, this modified resin was used to separate nitrate ions from sulfate ions in the aqueous solution.

Anion Exchange Resins↗
PubMed1986

Use of ion-exchange Sep-Pak cartridges in the batch fractionation of pituitary peptides.

Silica-based ion-exchange Sep-Pak cartridges, packed with either carboxymethyl (CM) cation-exchanger or a quaternary methyl ammonium (QMA) anion exchanger, are now available. The feasibility of using ion-exchange Sep-Pak cartridges for the fractionation of pituitary peptides was investigated. Extracts of bovine posterior pituitaries were fractionated at either pH 5 or pH 7 by pairs of cation and anion exchangers, connected in series. The capacity to bind peptides was well correlated with the theoretical charge calculated for a variety of peptides. At pH 5 the entire tissue extract could be fractionated into either basic or acidic pools. In contrast, at pH 7 only the more basic or acidic peptides were retained by the respective ion exchangers. The rest of the peptides passed through both ion exchangers and were recovered in the neutral pool. The ion-exchange fractionation principle was used to facilitate the purification of 35S-labelled intermediate pituitary glycopeptides, prepared by incubating mouse intermediate lobes in explant culture with 35S-labelled sulphate. 35S-labelled glycosylated forms of Lys1 gamma 3MSH, corticotropin-like intermediate lobe peptide, and the amino terminal or 16K fragment of pro-opiomelanocortin (i.e. 16K1-74) were fractionated into separate pools such that they could be purified to homogeneity in a single step by reversed-phase high-performance liquid chromatography (RP-HPLC). Purification by conventional means would require at least two RP-HPLC steps. Thus, radiolabelled peptides can be purified with the minimum of chromatographic manipulation, thereby ensuring maximal recoveries.

Animals↗
PubMed2003

Ammonia removal from wastewater by ion exchange in the presence of organic contaminants.

The scope of this study was the removal of ammonium by ion exchange from simulated wastewater. The study looks at the effect of organics upon ammonium ion exchange equilibrium uptake. The ion exchangers included a natural zeolite clinoptilolite, and two polymeric exchangers, Dowex 50w-x8, and Purolite MN500. The organic compounds studied included citric acid and a number of proteins. The traditional method for removal of ammonium and organic pollutants from wastewater is biological treatment, but ion exchange offers a number of advantages including the ability to handle shock loadings and the ability to operate over a wider range of temperatures. The results show that in most of the cases studied, the presence of organic compounds enhances the uptake of ammonium ion onto the ion exchangers.

Ammonia↗
PubMed2006

Enhanced transscleral lontophoretic transport with ion-exchange membrane.

PURPOSE: Transscleral iontophoresis has been recently re-examined for drug delivery to the back of the eye. In conventional iontophoresis, due to the relatively high electromobility of the endogenous competing ions (counterions) relative to that of the drug ion in the tissue barrier, the efficiency of iontophoretic drug delivery is generally low. The objective of the present study was to examine ion-exchange membrane-enhanced transscleral iontophoretic transport in which the ion-exchange membrane in series with the sclera can hinder the transport of the competing counterions and selectively allow the transport of the permeant across the sclera. METHODS: The physical properties of the Ionac ion-exchange membrane and excised rabbit sclera were determined in equilibrium uptake experiments and in passive and iontophoretic transport experiments with salicylate, tetraethylammonium, urea, and mannitol. Transscleral experiments with the ion-exchange membrane were conducted with salicylate and excised rabbit sclera in vitro. The contribution of electroosmosis to electrotransport during transscleral iontophoresis was assessed with urea and mannitol. RESULTS: The ion-exchange membrane is highly positively charged and has a small effective pore size. The sclera is relatively porous with a large effective pore size and low pore tortuosity. The sclera is also net negatively charged but this does not significantly affect the transport of small ions. A three-fold steady-state transscleral flux enhancement of salicylate was observed in ion-exchange membrane-enhanced iontophoresis over conventional transscleral iontophoresis without the membrane. Such enhancement was relatively independent of the applied electric current density and the thickness of the studied ion-exchange membrane assembly. Although the ion-exchange membrane altered transscleral electroosmosis, the contribution of electroosmosis to electrotransport was not significant. CONCLUSIONS: The present study has demonstrated the potential of ion-exchange membranes for enhancing iontophoretic transport and drug delivery.

Animals↗
PubMed2004

Charge regulation in protein ion-exchange chromatography: development and experimental evaluation of a theory based on hydrogen ion Donnan equilibrium.

An extension of the stoichiometric displacement (SD) model for the ion-exchange adsorption of dilute proteins is developed which accounts for the effects of hydrogen ion Donnan equilibrium on the protein charge. The ability of the new model to fit retention data when the fluid phase pH is near the protein pI and the effects of hydrogen ion Donnan equilibrium are important is examined using four different proteins and four different column packings. The results indicate that the model is able to fit retention data using values for the protein pI and the change in protein charge with pH at the pI, i.e., (dz/dpH)pI, that are significantly closer to the values of these parameters determined by isoelectric focusing and acid-base titrametry in free solution, respectively, as compared to the values obtained by determining the characteristic binding change as a function of pH using the traditional stoichiometric displacement model. This suggests that when the fluid phase pH is near the protein pI, charge regulation is an important cause of the discrepancy between the electrical charge of a protein in free solution and the characteristic binding charge from the stoichiometric displacement model. The results also indicate that for the case where the fluid phase pH is near the protein pI, the new model accounts for the effect of charge regulation during protein ion-exchange adsorption more accurately than previous models in the literature.

Chromatography, Ion Exchange↗
PubMed2004

Removal of fluoride from water through ion exchange by mesoporous Ti oxohydroxide.

In our previous study, we found that Ti(OH)(4) exhibited fluoride ion exchange properties. In order to improve the ion exchange capacity, mesoporous Ti oxohydroxide (TiOx(OH)y) had been prepared by using dodecylamine as template. Zirconia and silica had been introduced into the mesoporous Ti oxohydroxide to enhance the ion exchange capacity. The mesoporous structure and the morphology of the mesoporous materials obtained were confirmed using XRD and SEM, respectively. A fluoride ion exchange study was done on each sample. Results showed that mesoporous Ti oxohydroxide containing zirconia exhibited the highest fluoride ion exchange capacity, as it has the smallest particle size, with high uniformity among the mesoporous materials prepared.

Fluorides↗