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PubMed1997

Capillary zone electrophoresis and ion-exchange capillary electrochromatography: analytical tools for probing the Hanford nuclear site environment.

Ion-exchange capillary electrochromatography (IE-CEC) is a relatively new separation technique based on the combination of ion-exchange chromatographic and electrophoretic separation mechanisms. IE-CEC offers both the efficiency of capillary electrophoresis and the selectivity and sample capacity of ion-exchange chromatography. The utility of the method was examined with I- and IO3-, which are common constituents of nuclear wastes at Hanford, Washington and other U.S. Department of Energy (DoE) sites, and ReO4-, a surrogate for TcO4-. The advantages and limitations of IE-CEC relative to capillary zone electrophoresis (CZE) are explored. The chief advantages are increased loading capacity and an alternative selectivity to that of CZE, in addition to increased efficiency (relative to conventional ion-exchange chromatography). The run-to-run reproducibility of IE-CEC, however, was found to be a limitation of the technique.

Chromatography, Ion Exchange↗
PubMed1975

[On bacterial aftergrowth in drinking and industrial water. II. Apparative and processing influence upon the growth and the possibility of disinfection of ion exchange resin filter systems (author's transl)].

The comparative examination of numerous ion exchange resin filter systems for discontinuous water softening on the market revealed that apparative and processing characteristics are of great influence upon the aftergrowth of bacteria in the water of ion exchange resin systems. Within the examination it was taken into consideration that on the end-delivery-tube of the water pipe with regard to the colony count the conditions were more unfavourable during the long standstill over a weekend (table 1) than during the week (table2). The less favourable conditions have therefore been examined separately. The work has been divided in six test series. In the first one 5 ion exchange resin systems the types A-E are simultaneously tested with regard to the colony count in the water at the inflow to the apparatus and after the passage of it; regeneration twice a week with sodium chloride. The data ascertained in the course of several weeks (without first data on mondays) and the separated mondays data are examined according to logarithmic transformation with the assistance of variance analysis and the Newman Keuls-test for differences. The results show (tab. 4 and 5) that apparative parameters and such relevant to the technical process (tab. 3) have an influence upon the bacterial after growth of the water. The most favourable ion exchange resin filter is type E because it shows more favourable values than all other systems and the tapwater. In the second test serie the systems A-E have been regenerated with 1% Chloramin T containing sodium chloride. The results show again the type E as the statistically significant most favourable system in comparison with the others and the tapwater. In the third test serie it has been examined whether the long period of standstill of the brine in the resin bed which has probably been responsible for the good results of the type E would lead to values just as favourable if transferred to another type of apparatus. ...

Bacteria↗
PubMed2002

Biological reduction of perchlorate in ion exchange regenerant solutions containing high salinity and ammonium levels.

The most promising technologies to remove perchlorate from water are ion exchange and biological reduction. Although successful, ion exchange only separates perchlorate from water; it does not eliminate it from the environment. The waste streams from these systems contain the caustic or saline regenerant solutions used in the process as well as high levels of perchlorate. Biological reduction could be used to treat the regenerant waste solutions from the ion exchange process. A treatment scheme, combining ion exchange and biodegradation, is proposed to completely remove perchlorate from the environment. Perchlorate-laden resins generate brines containing salt concentrations up to 6% or caustic solutions containing up to 0.5% ammonium. Both, high salt and ammonium hydroxide concentrations are potentially toxic to microorganisms. Therefore, the challenge of the proposed system is to find perchlorate reducing microorganisms that are effective under such stressful conditions. Preliminary results have shown that salt concentrations as low as 0.5% reduced the perchlorate biodegradation rate by 30%; salt concentrations greater than 1% decreased this rate to 40%. Although biodegradation was seen in ammonium levels of 0.4%, 0.6% and 1%, the perchlorate biodegradation rate was 90% of that at 0% ammonium hydroxide. Further research will focus on the isolation and/or acclimation of microorganisms that are able to biodegrade perchlorate under these stressful conditions.

Ammonium Hydroxide↗
PubMed2005

Effect of ion-exchange fiber structure on the binding and release of model salicylates.

Salicylates were used as model anions to evaluate the effect of the structure (framework and ion-exchange groups) of fibrous anion-exchangers on the extent and mechanism(s) of compound binding and release. Binding was affected by the physicochemical properties of both the salicylates and the ion-exchange fibers. The highest molar amount of binding was obtained with the most lipophilic salicylate (5-chlorosalicylic acid) and the weak base (vinylpyridine) anion-exchange fibers. However, when the ion-exchange capacity was taken into account, higher binding was obtained in fibers of poly(ethylene) framework compared to the viscose-based fibers. The extent of salicylate release into NaCl solution(s) was dependent on the physicochemical characteristics of both the fiber and the bound model salicylate as well as on the amount of extracting ions. With strong base fibers (trimethylammonium), the viscose framework released the salicylates more efficiently than the poly(ethylene) framework. In the case of weak base fibers, the poly(ethylene) framework released the salicylates to a higher extent than the viscose framework. Calculated equilibrium constants (K) of the ion-exchange reactions illustrated that in addition to electrostatic interactions (pure ion-exchange mechanism), non-electrostatic interactions (hydrophobic interactions and/or hydrogen bonding) were also involved. However, the release of the salicylates was efficiently modified by the amount of extracting electrolyte, demonstrating that ion-exchange was the prevalent release mechanism.

Anions↗
PubMed1994

Adsorption and ion-exchange isotherms in preparative chromatography.

A systematic characterization of ion-exchange and adsorption isotherms is presented. This treatment serves to emphasize the singular nature of monovalent ion-exchange and classical Langmuir isotherms, and describes the more general homovalent and heterovalent isotherms that are applicable to both ion-exchange and adsorption. Such formalisms are applied to adsorptive systems for the first time, and could prove to be useful additions to the canon of available isotherms. The shielding effect of macromolecular adsorbates on the binding of other macromolecules is discussed, and its parallel to the characteristic charge of a macromolecule is brought out. The application of the general adsorptive formalism to reversed-phase chromatography yields a relationship between the retention factor and the modifier concentration that, in two limiting cases, reduces to two well-known results. The first, which is characteristic of small molecules, gives a linear relationship between the logarithmic retention factor and a linear or quadratic term in the modifier. The second, which is characteristic of large molecules, gives a linear relationship between the logarithmic retention factor and the logarithm of the modifier concentration. The use of appropriate concentration units is shown to resolve certain apparently non-standard (non-Tiselian) displacement patterns. The measurement of characteristic charges by displacement described above could be an interesting complement to the more common elution method, and could provide further insight into the underlying physico-chemical phenomena.

Adsorption↗
PubMed2002

Improved stability and release control of levodopa and metaraminol using ion-exchange fibers and transdermal iontophoresis.

Achievement of controlled drug delivery and stability of drugs during storage is a problem also in transdermal drug delivery. The objective of this study was to determine, whether an easily oxidized drug, levodopa, could be stabilized during storage using pH-adjustment and ion-exchange fibers. Controlled transdermal delivery of the zwitterionic levodopa was attempted by iontophoresis and ion-exchange fiber. Ion-exchange kinetics and transdermal permeation of a cationic (presumably more stable) model drug, metaraminol, were compared to the corresponding data of levodopa. Levodopa was rapidly oxidized in the presence of water, especially at basic pH-values. At acidic pH-values the stability was improved significantly. Ion-exchange group and the pH had a clear effect on the release of both the levodopa and metaraminol from the ion-exchange fiber. The adsorption/release kinetics of metaraminol were more easily controllable than the corresponding rate and extent of levodopa adsorption/release. Iontophoretic enhancement of drug permeation across the skin was clearly more significant with the positively charged metaraminol than with the zwitterionic levodopa. Ion-exchange fibers provide a promising alternative to control drug delivery and to store drugs that are degraded easily.

Delayed-Action Preparations↗
PubMed2006

Ferrous-Ferric Ion exchange dosemeter.

In this work a three-dimensional ferrous-ferric ion exchange dosemeter is proposed and the dose response measured. The dosemeter consists of strong acid cation exchange resin beads in the H form in water. Amberlyst 15 Wet beads with a harmonic mean diameter of 0.600-0.850 mm were prepared by soaking them in an aqueous solution of ferrous ammonium sulphate to exchange ferrous ions for H(+) ions. The beads were rinsed with distilled water and packed in glass vials. Sets of samples with ferrous ion concentrations of 0.5 and 1.0 mM were dosed with 6 MV X rays from a Varian 2100C linac. The spin-lattice relaxation time constants (T1) for the samples were measured using an Apollo spectrometer (Tecmag, Houston, TX) interfaced to a 1.5 T magnet (Magnex, Abingdon, UK). Each sample had two T1 values; a long T1 at 1200 ms that did not significantly change with dose and a short T1 that ranged from 56 ms at 0 Gy to 36 ms at 100 Gy. The R1 vs. dose responses were linear with slopes of 0.066 and 0.079 s(-1) Gy(-1).

Dose-Response Relationship, Radiation↗
PubMed1994

Effect of grinding and fluoride-gel exposure on strength of ion-exchanged porcelain.

Strengthening of dental porcelain through a diffusion heat treatment at 450 degrees C of a potassium-enriched, ion-exchange surface coating has been demonstrated in several recent studies. However, little attention has been focused on the potential strength reduction of these materials when the treated surfaces are ground or etched under clinically simulated conditions. The objective of this study was to test the hypothesis that partial removal of the surface layers of ion-exchanged porcelains by grinding or exposure to acidulated fluoride gel will significantly reduce their flexure strength. Nine groups of body porcelain disks were ion-exchanged at 450 degrees C for 30 min. One of these groups was subjected to ion exchange and no further surface treatment. Eight specimen groups were subjected to the following procedures after ion exchange: grinding to depths of 50 microns, 100 microns, 150 microns, 200 microns, and 250 microns, and exposure to acidulated fluoride for 30 min, 60 min, and 300 min. A tenth group (FC) was fired at 960 degrees C and fast-cooled in air, but the disks were not subjected to the ion-exchange treatment. Surface stress was calculated from measured values of cracks induced in the treated surfaces. Fluoride exposure for up to 60 min resulted in a significant decrease in surface compression (P < or = 0.05), although this treatment had no effect on strength. Grinding to a depth of from 100 microns to 250 microns caused a significant decrease in strength, while removal of a 50-microns layer caused no significant change (P > 0.05).

Acidulated Phosphate Fluoride↗
PubMed2002

[The effect of ion-exchange technique on surface strengthening of dental ceramics].

OBJECTIVE: Observe the effect of the ion-exchange technique on the surface strengthening of the dental ceramics. METHODS: Prepare the standard samples of Vita VMK 95, Vita VMK68 and Shofu Vintage ceramics, 10 pieces for each ceramic. The samples were divided into experiment group and control group. The samples in the experiment group were spread with HX-I ion-exchange cataplasm, and strengthened at the same condition with the control group. Flexure strength and EMPA were tested. All the data were calculated with SPSS 10.0 Stat. Software. RESULTS: The flexure strength of the experiment group was higher than the control group(P<0.05). EMPA showed that the depth of Na(+)-->K(+) ion-exchange was more than 100microm. CONCLUSION: HX-I ion-exchange cataplasm can significantly improve the flexure strength of dental ceramics and get an evident Na(+)-->K(+) ion-exchange.

English Abstract↗
PubMed1999

Characterization of unstable ion-exchange chromatographic separation of proteins.

Very fine separation of proteins by stepwise elution ion-exchange chromatography is very often a unstable process. To characterize the unstability of such processes the elution volume variations were examined by the model equation which contained the ion-exchange capacity and the number of adsorption sites. The data needed for the model calculation were obtained from gradient elution experiments. As a model separation system stepwise elution of a model protein (beta-lactoglobulin) near the isoelectric point on a weak cation-exchange chromatography column was chosen. The elution volume varied significantly with a small change in the ion-exchange capacity. It was found that the ionic strength of the elution buffer must be adjusted in order to compensate a change in the elution volume due to the ion-exchange capacity variations. The ionic strength and the pH of the elution buffer were also found to be important variables affecting the elution volume. In this model separation system, it was indicated that the pH should be within +/-0.1 unit and the ionic strength within +/-0.002 mol/l in order to meet the criteria (+/-5% elution volume variation). It is recommended that gradient elution data be obtained for predicting elution volume variations in stepwise elution. By using the gradient elution data the process diagnosis can be performed, and the important information on the process stability can be obtained.

Chromatography, Ion Exchange↗
PubMed1986

Direct assay of thymidine kinase bound to ion-exchange paper for dot spotting and enzyme blotting analysis.

The direct assay of thymidine kinase (Tk) bound to ion-exchange paper was investigated as a means to further simplify the analytical procedure. Thymidine kinase bound firmly and quantitatively to ion-exchange paper at near neutral pH. The enzymatic properties of Tk did not change while bound to the ion-exchange paper. The amount of phosphorylated 125IdU or 125IdC formed on ion-exchange paper was proportional to the amount of applied Tk. Enzymatic activity could be determined visually by autoradiography or by gamma counting. This method was relatively independent of the protein concentration or volume of the sample and which allows the assay from dilute solutions. A simplified dot spot method that can be used for the assay of thymidine kinase activity in cell extracts is described. Thymidine kinase could also be visualized after electrophoresis and blotting on ion-exchange paper.

Animals↗
PubMed1999

Surface Hydroxyl Site Densities on Metal Oxides as a Measure for the Ion-Exchange Capacity.

Hydroxyl groups on metal oxide in water are the sites for ion exchange, and the surface hydroxyl site density on oxides is a measure of the ion-exchange capacity. Here, the Grignard reagent method was applied to determine the surface hydroxyl site density of oxide samples. The results were similar to those reported for different oxides with other methods (dehydration by heating, tritium exchange, crystallographic calculations, etc.), and they are comparable with those calculated from the closest packing of hydroxide ions. A mechanism of hydroxylation is proposed: lattice oxide ions (extremely strong bases) are exposed to aqueous solutions and are neutralized by water to become hydroxide ions. Also, the saturated deprotonation method was applied to hematite, and it was found that all the acid hydroxyl groups on hematite were deprotonated in very high concentrations of alkali solutions ( approximately 5 mol dm-3 NaOH), and from the saturated amount of OH- consumed by deprotonation, the same result as that by the Grignard method was obtained. It is shown that all hydroxyl groups take part in ion exchange and that the unusually small values reported elsewhere with the saturated (de)protonation method may contain errors. Hetero- or homogeneity of hydroxyl groups in contact with water as ion-exchange sites is also discussed. It is suggested that intensely hydrated layers at the oxide/water interface may result in homogeneous discrete sites. The development of microstructures in the oxides was suggested from the measured values of specific surface areas, and the effect of the microstructure environments on the reactivity of internal surface hydroxyl sites is discussed. Copyright 1999 Academic Press.

Journal Article↗
PubMed1989

Purification of synthetic oligonucleotides on a weak ion-exchange column.

A weak ion-exchange column (PVDI 4000-5) was used to purify oligonucleotides of relatively large size. The purification of polynucleotides was very rapid, they were separated according to size and retained all their properties relevant to genetic engineering experiments.

Chromatography, Ion Exchange↗
PubMed2004

Ion exchange using poorly activated supports, an easy way for purification of large proteins.

Ion-exchange chromatography using commercial ionic supports is a commonly used technique for protein purification. However, selective adsorption of a target protein from a given extract onto commercial ion exchangers seems to be quite complex since they are designed to adsorb the maximum percentage of proteins with the opposite charge. In this paper, ion-exchanger supports with different activation degrees (from 1 to 40 micromol of amino groups per g of agarose) have been prepared and used for the purification of large proteins. These kinds of proteins have large surfaces to interact by many points with the support. Therefore, it was possible to purify large proteins as beta-galactosidase from Thermus sp. strain T2 from a crude extract from Escherichia coli or bovine liver catalase from a commercial preparation, with tailor-made ion-exchanger supports. A simple step of adsorption/desorption on lowly activated supports rendered both enzymes rather pure as confirmed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Moreover, this strategy makes also easy the desorption step that requires rather low NaCl concentrations, which may become a serious problem for desorption of large proteins when using conventional supports, due to their ability of generating a very strong adsorption.

Chromatography, Gel↗
PubMed1989

Determination of homocysteine in plasma by ion-exchange chromatography.

A rapid ion-exchange chromatographic method for determination of total homocysteine in plasma is presented. The method has a coefficient of variation of approximately 5%. A comparison with a slower method previously used in our laboratory showed a high correlation (r = 0.993). The risk of oxidation of homocysteine during the chromatography and the necessary level of dithiotreithol to prevent oxidation are also established.

Chromatography, Ion Exchange↗