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PubMed2002

Comparison of linear gradient and displacement separations in ion-exchange systems.

The linear gradient mode of chromatography is the most widely employed mode of operation in ion-exchange chromatographic separations. However, in recent years, the displacement mode has received considerable attention because of its promise of high throughput and high resolution. To enable a comparison of these two modes of chromatography, it is essential to identify the optimum operating conditions for each. We employed an iterative algorithm to carry out the necessary optimization. The Steric Mass Action model of ion-exchange chromatography is used in concert with the solid-film linear-driving force model to describe the chromatographic behavior of the solutes in these systems. The performances of displacement and gradient modes of chromatography are compared for different types of separation problems. It turns out that for "easy" separations, both the modes are equally effective. However, for challenging separations, the displacement mode is superior to the gradient mode. Our results shed significant light on the performance of gradient and displacement modes in protein ion-exchange systems.

Adsorption↗
PubMed1998

The effect of monoclonal or ion-exchange purified factor VIII concentrate on HIV disease progression: a prospective cohort comparison.

The CD4 count has been reported to decline less rapidly in HIV-infected haemophiliacs treated with monoclonally purified factor VIII concentrates than in those using intermediate-purity concentrates. No survival advantage has been demonstrated for this effect, and it is unclear whether this effect occurs with all high-purity concentrates. Two cohorts of patients with severe haemophilia A and HIV treated with either ion-exchange-purified or monoclonally-purified concentrates were compared. The CD4 count, survival, AIDS-defining illnesses, CDC category and anti-retroviral therapy were recorded at 6-monthly intervals for 3 years following the change from intermediate to high-purity factor VIII. 116 patients were recruited, 37 of whom were treated with an ion-exchange purified factor VIII concentrate at three centres, mean (SD) age 31.1 (12.2) years, and 79 were treated with monoclonally purified factor VIII concentrate at two centres, mean (SD) age 29.8 (11.2) years. At the start of the study the median CD4 count was (monoclonal v ion-exchange) 0.30 v 0.16 x 10(9)/l. The CD4 count declined in both arms to a median of (monoclonal v ion-exchange) 0.16 v 0.08 x 10(9)/l at the final visit. Analysis of the (CD4 count)(1/2) over time, using a random coefficients model, found that the mean (SE) rates of decline were not statistically significantly different in the two treatment groups (monoclonal v ion exchange: -0.050 (0.008) v -0.034 (0.011) (CD4 count)(1/2) per year, P = 0.24). No statistically significant difference in survival (log-rank test: P = 0.33) was found. There was no difference in the proportion of individuals experiencing one or more AIDS-defining illnesses (P = 0.32) or in the proportion progressing to CDC category IV (P = 0.28) during the study. The CD4 count declined during the study at a rate similar to that previously reported in patients treated with intermediate-purity factor VIII concentrate, and there was no evidence of any difference between the two treatment groups.

Blood Component Transfusion↗
PubMed1997

Post-thaw plasma membrane integrity of bull spermatozoa separated with a Sephadex ion-exchange column.

Previous experiments have established that filtration of bovine semen through a Sephadex ion-exchange column improves its quality before and after freezing. The present study was conducted to determine the post-thaw membrane integrity of bull spermatozoa separated with a Sephadex ion-exchange column and to determine the kind of protection to spermatozoa is provided by glycerol during freezing and thawing. Semen from Holstein bulls diluted in TEST-yolk extender (with and without glycerol) was filtered through a Sephadex ion-exchange column and frozen in liquid nitrogen (-196 degrees C). After thawing, there were more normal acrosomes in filtered spermatozoa than nonfiltered (P < 0.01). Post-thaw plasma membrane integrity and swelling ability in a hypoosmotic solution revealed that the filtered spermatozoa had a stronger (P < 0.005) plasma membranes than the nonfiltered. Filtered spermatozoa demonstrated higher zona-free hamster oocyte penetration than the nonfiltered (30.5 vs 11.5%; P < 0.0005). Spermatozoa extended in TEST-yolk without glycerol had the lowest (P < 0.001) normal acrosomes, intact plasma membranes and swelling ability. Plasma membrane over the post-acrosomal region of the head and post-midpiece region of the tail was more sensitive to damages caused by freezing and thawing than acrosomal and midpiece regions of spermatozoa. Glycerol in the extender provided significant (P < 0.05) protection to the sensitive regions of filtered and nonfiltered spermatozoa during freezing and thawing. Filtered plus glycerolated spermatozoa had the highest (P < 0.01) normal acrosomes, intact plasma membranes and swelling ability. In conclusion, the pre-freezing filtration of bovine semen harvested the spermatozoa possessing stronger plasma membranes which enabled them to endure freezing and thawing stresses. The addition of glycerol to the extender protected the post-acrosomal region of the head and post-midpiece region of the tail of spermatozoa from freezing and thawing shocks.

Journal Article↗
PubMed2005

Ion exchange recovery of Ni(II) from simulated electroplating waste solutions containing anionic ligands.

Ion exchange is widely used for the recovery and removal of metals from process and waste streams in chemical process industries. The Na-form of strong-acid Purolite NRW-100 resin was used to recover Ni(II) from a simulated electroplating waste solution containing NiSO4, NH4Cl, NaH2PO4, and citrate. A set of mass balance equations that take into account possible aqueous complexation reactions was used to establish the pH diagram of Ni(II) species in the presence of anionic ligand citrate or phosphate. Experiments were performed as a function of initial solution pH (0.5-6.0), initial concentration of Ni(II) (0.85-11.9 mol/m3), and temperature (15-45 degrees C). It was shown that the amount of Ni(II) exchanged leveled off when the equilibrium pH was higher than around 2.5. The exchange isotherms obtained at various equilibrium pH values were well fitted by the Langmuir equation. The enthalpy of Ni(II) exchange was also evaluated based on the Langmuir constant. Finally, the kinetics of the present ion exchange process was analyzed.

Anions↗
PubMed2005

A priori prediction of adsorption isotherm parameters and chromatographic behavior in ion-exchange systems.

The a priori prediction of protein adsorption behavior has been a long-standing goal in several fields. In the present work, property-modeling techniques have been used for the prediction of protein adsorption thermodynamics in ion-exchange systems directly from crystal structure. Quantitative structure-property relationship models of protein isotherm parameters and Gibbs free energy changes in ion-exchange systems were generated by using a support vector machine regression technique. The predictive ability of the models was demonstrated for two test-set proteins not included in the model training set. Molecular descriptors selected during model generation were examined to gain insights into the important physicochemical factors influencing stoichiometry, equilibrium, steric effects, and binding affinity in protein ion-exchange systems. The a priori prediction of protein isotherm parameters can have direct implications for various ion-exchange processes. As proof of concept, a multiscale modeling approach was used for predicting the chromatographic separation of a test set of proteins using the isotherm parameters obtained from the quantitative structure-property relationship models. The simulated column separation showed good agreement with the experimental data. The ability to predict chromatographic behavior of proteins directly from their crystal structures may have significant implications for a range of biotechnology processes.

Adsorption↗
PubMedDate not supplied

Preparation of bioconjugates by solid-phase conjugation to ion exchange matrix-adsorbed carrier proteins.

A solid-phase conjugation method utilizing carrier protein bound to an ion exchange matrix was developed. Ovalbumin was adsorbed to an anion exchange matrix using a batch procedure, and the immobilized protein was then derivatized with iodoacetic acid N-hydroxysuccinimid ester. The activated protein was conjugated with glutathione, the conjugation ratio determined by acid hydrolysis, and amino acid analysis performed with quantification of carboxymethyl cysteine. Elution of conjugates from the resin by a salt gradient revealed considerable heterogeneity in the degree of derivatization, and immunization experiments with the eluted conjugates showed that the more substituted conjugates gave rise to the highest titers of glutathione antibodies. Direct immunization with the conjugates adsorbed to the ion exchange matrix was possible and gave rise to high titers of glutathione antibodies. Conjugates of ovalbumin and various peptides were prepared in a similar manner and used for production of peptide antisera by direct immunization with the conjugates bound to the ion exchanger. Advantages of the method are its solid-phase nature, allowing fast and efficient reactions and intermediate washings, and the ability to release conjugates from the solid phase under mild conditions.

Adjuvants, Immunologic↗
PubMed1997

Preparation and use of ion-exchange chromatographic supports based on perfluoropolymers.

A poly(vinyl alcohol) (PVA) coated particulate perfluoropolymer (FEP) support has been functionalised with ion-exchange groups for use in ion-exchange chromatography of proteins. Anion-exchange (DEAE and Q) and cation-exchange (SP) groups were introduced to PVA-FEP which had previously been activated using cyanuric chloride. The equilibrium adsorption capacities of SP-PVA-FEP were 31.8 and 25.2 mg ml-1 for lysozyme and IgG respectively while for DEAE-PVA-FEP, the equilibrium adsorption capacities were 14.9 and 9.7 mg ml-1 for beta-lactoglobulin and HSA respectively. The equilibrium adsorption capacities for Q-PVA-FEP were determined to be 17.2 and 13.5 mg ml-1 for beta-lactoglobulin and HSA respectively. Experiments carried out to investigate the resolving power of materials showed that both SP and Q-PVA-FEP were able to resolve proteins with only small differences in their isoelectric points and that this resolution could be maintained at a flow-rate of 1500 cm h-1. SP-PVA-FEP was used to purify lysozyme from egg whites where a 50-fold purification, to homogeneity, was achieved in 98% yield. The anion exchanger, Q-PVA-FEP could be used to purify G6PDH from a clarified homogenate of bakers' yeast 14.3-fold in 81% yield.

Adsorption↗
PubMed2004

New ion exchange materials for use in a 82Sr/82Rb generator.

82Rb is a short-lived positron-emitting isotope (T1/2 = 75 s) that is increasingly being used in positron emission tomography for the evaluation of myocardial perfusion. The short half-life of 82Rb results in rapid decay of the administered radioactivity allowing repeat scans to be performed after a relatively short time interval. The 82Rb is available from a 82Sr/82Rb generator in which the 82Sr parent is immobilized on an ion exchange column and 82Rb eluted when required. Consequently, suitable ion exchangers for use in a generator must have a very high affinity for strontium and a negligible affinity for rubidium, allowing the pure 82Rb to be safely and efficiently eluted in high yields. This study evaluated a number of strontium-selective ion exchange materials using batch experiments and identified sodium nonatitanate as the best material for use in a 82Sr/82Rb generator.

Chromatography, Ion Exchange↗
PubMed1989

Determination of iron species in wine by ion-exchange chromatography--flame atomic absorption spectrometry.

The direct coupling of ion-exchange chromatography to flame atomic absorption spectrometry (AAS) has been achieved by employing a Babington type nebuliser. The system enables all the processes on the column to be followed directly at flow-rates of between 1 and 5 ml min-1. The potential of the system was investigated for the determination of various iron species in synthetic samples containing iron(II) and iron(III) in ionic or chelated form by employing various ion-exchange (Dowex 50-X8, Dowex 1-X8) and sorptive (Amberlite XAD-2) resins, respectively. In some instances where direct coupling was impossible, owing to the physical properties of the effluent or eluent, conventional analyses of chromatographically separated iron species were performed by flame AAS. The optimum concentration range, limit of detection and reproducibility of measurement were also determined for a particular column capacity. When direct coupling was employed, the detection limit for the separated iron species was 15 micrograms with a relative standard deviation (RSD) of +/- 3% and, using the conventional method of analysis, 2-5 micrograms with an RSD of +/- 1%. On the basis of these results the system was applied to the determination of the ratio of iron(II) to iron(III) in wines.

Chromatography, Ion Exchange↗
PubMedDate not supplied

[Ion-exchange properties of DNA immobilized in acrylamide gel].

Ion-exchange of K+, Ca2+, Mg2+ and NH4+ on the Na+-DNA entrapped in acrylamide gel was studied. Under a definite percentage ratio between acrylamide and cross-linking agent (N,N'-methylenebisacrylamide) more than 95% of initial DNA was shown to be immobilized firmly and not to be washed out by salt solutions. Melting temperature and hypochromicity measurements of DNA extracted from the gel showed that denaturation of DNA has not taken place. The gel with immobilized DNA may be considered as ion-exchanger with phosphate fixed groups. It has been found that Mg2+, Ca2+, Na/, K+ and NH4+ are bounded with phosphate groups only, the degree of binding declines in the following order: Na+ less than or equal to K+ much less than Mg2+ less than Ca2+. The immobilization of DNA is suggested as a method of investigation of interaction between DNA and metal ions.

Acrylamides↗
PubMed1995

Rapid purification of tubulin from tissue and tissue culture cells using solid-phase ion exchange.

Tubulin can be purified from tissue or tissue culture cell starting material in less than 6 h using a combination of a solid-phase ion exchanger and one cycle of temperature-dependent polymerization and depolymerization. The use of a solid-phase ion exchanger (MemSep DEAE) greatly reduces the time required for the ion exchange step compared to conventional exchangers. The use of sodium glutamate to elute tubulin from the exchanger stabilizes the protein and facilitates the final polymerization step of the purification. The procedure can be performed successfully with less than 100 mg of tissue culture cell protein as starting material. The final material is > 90% pure and active as judged by sodium dodecyl sulfate-gels and by binding of the bicyclic colchicine analog 2-methoxy-5-(2',3',4'-trimethoxyphenyl)-tropone.

Animals↗
PubMed1990

High-performance liquid chromatography of amino acids, peptides and proteins. CIII. Mass transfer resistances in ion-exchange and dye-affinity chromatography of proteins.

Adsorption equilibria and rate kinetics have been investigated for the binding of several proteins, with different molecular geometries, to several ion-exchange and dye-affinity chromatographic resins with varying pore size and protein accessibilities. The pore geometry was shown to play a significant role in the protein capacity and loadability of both the ion-exchange and dye-affinity resins. For example the Fractogel HW75-Cibacron Blue F3GA affinity sorbent had the greatest capacity for the small protein, lysozyme, compared to the other Fractogel HW-Cibacron Blue F3GA sorbents, and similarly, the ion-exchange resins, such as DEAE-Fractogel 65, bound more human serum albumin (HSA), as opposed to the larger protein, ferritin. The apparent diffusion of protein from the bulk phase to the ligands/ionic sites was calculated to be considerably restricted when the pore to protein size ratio was small, as is the case of DEAE Fractogel 65/ferritin system, and the dye-affinity Fractogel HW55/HSA system. In these circumstances, pore diffusivity was calculated to be up to 100-fold smaller than bulk diffusivity.

Adsorption↗
PubMed2006

Incorporating water-release and lateral protein interactions in modeling equilibrium adsorption for ion-exchange chromatography.

The equilibrium adsorption of two albumin proteins on a commercial ion exchanger has been studied using a colloidal model. The model accounts for electrostatic and van der Waals forces between proteins and the ion exchanger surface, the energy of interaction between adsorbed proteins, and the contribution of entropy from water-release accompanying protein adsorption. Protein-surface interactions were calculated using methods previously reported in the literature. Lateral interactions between adsorbed proteins were experimentally measured with microcalorimetry. Water-release was estimated by applying the preferential interaction approach to chromatographic retention data. The adsorption of ovalbumin and bovine serum albumin on an anion exchanger at solution pH>pI of protein was measured. The experimental isotherms have been modeled from the linear region to saturation, and the influence of three modulating alkali chlorides on capacity has been evaluated. The heat of adsorption is endothermic for all cases studied, despite the fact that the net charge on the protein is opposite that of the adsorbing surface. Strong repulsive forces between adsorbed proteins underlie the endothermic heat of adsorption, and these forces intensify with protein loading. It was found that the driving force for adsorption is the entropy increase due to the release of water from the protein and adsorbent surfaces. It is shown that the colloidal model predicts protein adsorption capacity in both the linear and non-linear isotherm regions, and can account for the effects of modulating salt.

Adsorption↗
PubMed1998

Preparation of and optimal module housings for hollow fibre membrane ion exchangers.

Macroporous polyamide 6 hollow fibres can be polymer coated by a three-step procedure: first, reaction of the amino end groups with a bifunctional, double-bond-containing reagent; second, block polymerization with different monomers; and third, polymer analogue reactions with amines or sulphite salts to produce ion exchanger groups. The densities of double bonds are dependent on the amino densities and are in the range of 20-30 mumol/g polyamide 6. The ion exchanger fibres were packed in different types of module housings to get an optimal separation unit. The best housing seems to be a so-called single-dead-end arrangement of fibres. Three types of ion exchanger hollow fibres have been produced: a weak and a strong anion exchanger and a strong cation exchanger. The dynamic protein-binding capacities are in the range of 40 mg/ml membrane. Using these membrane modules, it is possible to separate proteins in the same way as with particle-based ion exchangers. Fast protein separations with low pressure drop are possible.

Animals↗
PubMed1988

Rate of release of organic carboxylic acids from ion-exchange resins.

Organic anions with similar properties, but different molecular weights, were bound to anion-exchange resins with different cross-linking. It was found that the capacity of the ion-exchange resin for the anions, the percentage of organic anion released, and the rate of release depends on the crosslinking of the ion-exchange resin, the molecular weight of the anion, and the moisture content of the resin. Self-diffusion coefficients for the release rates were determined.

Anion Exchange Resins↗
PubMed1990

Ion exchange in purification.

Biochemicals have large complex three-dimensional structures with multiple weak acid and weak base groups on their surfaces. The ionization of these groups results in heterogeneous charge structures and complex ion-exchange equilibria. In this chapter the ion-exchange equilibria of amino acids are reviewed first. The ionization of the alpha-COOH group has a strong effect on the apparent equilibrium affinities of amino acids. Salt concentration and pH can also significantly affect the apparent affinities and valences. The implications on the ion-exchange equilibria of peptides and proteins are discussed. The second focus of this chapter is on the local equilibrium models of multicomponent chromatographic processes. The differences between unidirectional and two-way flow conditions, linear and nonlinear systems, elution and displacement processes, and isocratic and gradient operations are discussed. Fundamental analysis of these phenomena is applied to formulate strategies to shorten cycle time, improve resolution, raise product concentration, and increase throughput.

Amino Acids↗