Perchlorate adsorption and desorption on activated carbon and anion exchange resin

The mechanisms of perchlorate adsorption on activated carbon (AC) and anion exchange resin (SR-7 resin) were investigated using Raman, FTIR, and zeta potential analyses. Batch adsorption and desorption results demonstrated that the adsorption of perchlorate by AC and SR-7 resin was reversible. The reversibility of perchlorate adsorption by the resin was also proved by column regeneration test. Solution pH significantly affected perchlorate adsorption and the zeta potential of AC, while it did not influence perchlorate adsorption and the zeta potential of resin. Zeta potential measurements showed that perchlorate was adsorbed on the negatively charged AC surface. Raman spectra indicated the adsorption resulted in an obvious position shift of the perchlorate peak, suggesting that perchlorate was associated with functional groups on AC at neutral pH through interactions stronger than electrostatic interaction. The adsorbed perchlorate on the resin exhibited a Raman peak at similar position as the aqueous perchlorate, indicating that perchlorate was adsorbed on the resin through electrostatic attraction between the anion and positively charged surface sites.

Sorption of Cr(VI) ions on two Lewatit-anion exchange resins and their quantitative determination using UV-visible spectrophotometer

The sorption of Cr(VI) from aqueous solutions with macroporous resins which contain quarternary amine groups (Lewatit MP 64 and Lewatit MP 500) was studied at varying Cr(VI) concentration, adsorbent dose, pH, contact time and temperature. Batch shaking sorption experiments were carried out to evaluate the performance of Lewatit MP 64 and Lewatit MP 500 anion exchange resins in the removal of Cr(VI) from aqueous solutions. The concentration of Cr(VI) in aqueous solution was determined by UV-visible spectrophotometer. The ion exchange process, which is dependent on pH, showed maximum removal of Cr(VI) in the pH range 3-7 for an initial Cr(VI) concentration of 1x10(-3) M. The optimum pH for Cr(VI) adsorption was found as 5.0 for Lewatit MP 64 and 6.0 for Lewatit MP 500. The maximum Cr(VI) adsorption at pH 5.0 is 0.40 and 0.41 mmol/g resin for Lewatit MP 64 and Lewatit MP 500 anion exchangers, respectively. The maximum chromium sorption occurred at approximately 60 min for Lewatit MP 64 and 75 min for Lewatit MP 500. The suitability of the Freundlich and Langmuir adsorption models was also investigated for each chromium-sorbent system. The uptake of Cr(VI) by the anion exchange resins was reversible and so it has good potential for the removal of Cr(VI) from aqueous solutions. Both ion exchangers had high bonding constants but Lewatit MP 500 showed stronger binding. The rise in the temperature caused a slight decrease in the value of the equilibrium constant (K(c)) for the sorption of Cr(VI) ion.

Nitrosamine, dimethylnitramine, and chloropicrin formation during strong base anion-exchange treatment

Strong base anion-exchange resins represent an important option for water utilities and homeowners to address growing concerns with nitrate, arsenate, and perchlorate contamination of source waters. Most commercially available anion-exchange resins employ quaternary amine functional groups. Previous research has provided contradictory evidence regarding whether these resins serve as sources of nitrosamines, considered as highly carcinogenic nitrogenous disinfection byproducts (N-DBPs), even without disinfectants. For three common varieties of commercial anion-exchange resins, we evaluated the importance of releases of nitrosamines, and two other N-DBPs (dimethylnitramine and chloropicrin), when the resins were subjected to typical column flow conditions with and without free chlorine or chloramine application upstream or downstream of the columns. In the absence of disinfectants, fresh trimethylamine- and tributylamine-based type 1 and dimethylethanolamine-based type 2 anion-exchange resins usually released 2-10 ng/L nitrosamines, likely due to shedding of manufacturing impurities, with excursions of up to 20 ng/L following regeneration. However, the lack of significant nitrosamine release in a full-scale anion-exchange treatment system after multiple regeneration cycles indicates that releases may eventually subside. Resins also shed organic precursors that might contribute to nitrosamine formation within distribution systems when chloramines are applied downstream. With free chlorine or chloramine application upstream, nitrosamine concentrations were more significant, at 20-100 ng/L for the type 1 resins and approximately 400 ng/L for the type 2 resin. However, chloropicrin formation was lowest for the type 2 resin. Dimethylnitramine formation was significant with free chlorine application upstream but negligible with chloramines. Although no N-DBPs were detected in cation-exchange-based consumer point-of-use devices exposed to chlorinated or chloraminated waters, our results indicate that inclusion of anion-exchange resins in these devices, as in laboratory deionized water systems, would likely be problematic.

Modeling, rate-limiting step investigation, and enhancement of the direct bio-regeneration of perchlorate laden anion-exchange resin

Anion-exchange with high perchlorate affinity resins is one of the most promising technologies for removing low levels of perchlorate. However, the traditional brine desorption technique is difficult and costly for regeneration of this type of resin. Previously, a direct bio-regeneration method by contacting the spent high perchlorate affinity resin with the perchlorate-reducing bacteria was proved feasible. This research is a further study of that method. Firstly, a direct bio-regeneration process model, based on the physicochemical and biological fundamentals, was developed and calibrated with experimental data. Thereafter, the rate-limiting step in regeneration of the high perchlorate affinity resin was investigated. Methods to enhance the regeneration efficiency were developed. The results indicated that the calibrated model well described the regeneration process. It thus might provide useful insights into the regeneration system. The results also demonstrated that the perchlorate desorption from the loaded resin could be the rate-limiting step. Addition of proper amount of counter anions such as chloride and sulfate improved the regeneration efficiency because these anions could promote both the extent and rate of perchlorate desorption from the loaded resin. These findings aided us in achieving good and efficient regeneration of high perchlorate affinity resins like the A-530E and SR-7 resins. The findings also suggested that the application of bacteria that could efficiently reduce perchlorate in highly saline solution would make the method more promising for the regeneration of high perchlorate affinity resins.

Removal and recovery of phosphate from municipal wastewaters using a polymeric anion exchanger bound with hydrated ferric oxide nanoparticles

A new type of ion exchange media which is highly selective for phosphate, and can be easily regenerated has been investigated. The media consists of hydrated ferric oxide nanoparticles dispersed within the pore structures of polymeric anion exchanger beads. The media combines the durability and mechanical strength of ion exchange resins with the high sorption capacity of ferric oxide for phosphate. The media was trialled in fixed bed mini column experiments with real final effluent from two UK sewage treatment works, one with treatment based on chemical precipitation with iron chloride salts into an activated sludge process (population >250,000), and one based on trickling filter treatment with no specific phosphorus removal process (population <10,000). Results show that the media has high capacity for removing phosphate, reaching capacity at 4000 and 1300 bed volumes for the chemical precipitation and trickling filter works respectively, with performance greatly exceeding that of a standard anion exchanger, Amberlite IRA-410. Also trialled was the media's ability to elute the phosphorus after breakthrough, with the aim of recovering and processing it into a useful product. A one step regenerative process using a single solution containing 4% NaOH and 2% NaCl was passed through the resin bed and the phosphorus concentration of each bed volume leaving the column analysed. 80% of the phosphorus was eluted in the first bed volume. Subsequent tests investigated the performance of the media after successive partial regenerations of one bed volume of the NaOH/NaCl solution. There was no loss of performance observed after ten regeneration cycles, and levels of eluted phosphate were consistently high. These results suggest that the media has high potential for the removal and recovery of phosphate from wastewater streams. Additionally, the small volume of regenerant required translates to a very small operational footprint.

Studies of removal of palladium(II) ions from chloride solutions on weakly and strongly basic anion exchangers

Palladium and its compounds find wide application in industry as a catalytic agent in different manufacture processes. Recovery of precious metals from industrial wastes is difficult and time consuming but in spite of these disadvantages it becomes profitable. Palladium(II) ions sorption from various chloride solutions of the composition: 0.1-6.0M HCl-0.00056 M Pd(II), 1.0M ZnCl(2)-0.1M HCl-0.00056 M Pd(II), 1.0M AlCl(3)-0.1M HCl-0.00056 M Pd(II) on the weakly and strongly basic anion exchangers (Varion ATM, Varion ADM and Varion ADAM) was discussed. The sorption research of Pd(II) ions on these resins was carried out by means of static and dynamic methods. The dynamic processes were applied in order to determine the breakthrough curves of Pd(II) ions. Moreover, the working ion-exchange capacities as well as the weight and bed distribution coefficients were determined from the Pd(II) breakthrough curves. The recovery factors of Pd(II) ions (% R) depending on the phase contact time were obtained by means of static methods. The highest ion-exchange capacities for the 0.1-6.0M HCl-0.00056 M Pd(II) systems were obtained for the weakly basic ion-exchange resin Varion ADAM.

Solid-phase extraction of copper, iron and zinc ions on Bacillus thuringiensis israelensis loaded on Dowex optipore V-493

Bacillus thuringiensis israelensis loaded on Dowex optipore V-493 as new adsorbent for the separation-preconcentration of heavy metal ions has been proposed. The analytical conditions for the quantitative recoveries of copper(II), iron(III) and zinc(II) including pH, amounts of adsorbent, sample volume, etc. were investigated. The influences of alkaline and earth alkaline ions were also reported. The recovery values for the analytes are generally higher than 95%. The preconcentration factor was 37. The limit of detections of the analyte ions (k=3, N=21) were 1.14 microgL(-1) for copper, 2.01 microgL(-1) for iron and 0.14 microgL(-1) for zinc. The relative standard deviations of the determinations were found to be lower than 9%. The procedure was validated by analyzing copper, iron and zinc contents in two certified reference materials, NRCC-SLRS-4 Riverine water and NIST SRM 1515 Apple leaves. Agreements between the obtained results and the certified values were achieved. The developed preconcentration method was applied in the flame atomic absorption spectrometric determination of copper, iron and zinc in several samples including a multivitamin-multimineral tablet, dialysis solutions, natural waters and some food samples.

Feasibility and kinetics study on the direct bio-regeneration of perchlorate laden anion-exchange resin

Anion exchange is one of the most promising treatment technologies for the removal of low levels of perchlorate. The spent anion-exchange resins, however, need to be disposed of or regenerated because they contain high contents of perchlorate. This study investigated the feasibility and kinetics of a direct bio-regeneration method. The method accomplished resin regeneration and biological perchlorate destruction concurrently, by directly contacting the spent resin with the perchlorate-reducing bacteria (PRB). The results indicated that the method was effective in regeneration of perchlorate and nitrate loaded resin and the resin could be repeatedly regenerated with the method. The regenerated resin was effective, stable, and durable in the filtration treatment of perchlorate in well water from the Saddle River area, NJ. Moreover, the method was also effective in regeneration of the spent A-530E resin, which had high perchlorate affinity and was yet very difficult for regeneration with the conventional brine desorption technique. Besides, the results further suggested that the perchlorate and nitrate desorption from the loaded resin coupling with their subsequent biological reduction could be the direct bio-regeneration mechanism. No biofilm was formed on the regenerated resin surface according to a scanning electron microscopy (SEM) analysis.

Reversible Immobilization of Glutaryl Acylase on Sepabeads Coated with Polyethyleneimine

The immobilizaton of the enzyme glutaryl-7-aminocephalosporanic acid acylase (GA) was performed via ionic adsorption onto several supports: a new anionic exchange resin, based on the coating of Sepabeads internal surfaces with polyethyleneimine (PEI) of different molecular weights, and conventional EC-Q1A-Sepabeads and DEAE-agarose. Immobilization occurred very rapidly in all cases, but the adsorption strength was much higher in the case of PEI-Sepabeads than in the other supports at pH 7 (e.g., at 150 mM NaCl, 90% of the enzyme was eluted from the DEAE agarose and 15% was eluted from the EC-Q1A-Sepabeads, whereas no desorption was detected with the best PEI-Sepabeads). Interestingly, the adsorption strength of the GA was increased when it was immobilized on PEI-Sepabeads with higher molecular weights. For instance, enzyme desorption was detected from 75 mM NaCl for the derivative prepared onto Sepabeads coated with PEI 700 Da, whereas in the derivative prepared with the highest molecular weight PEI (600 000 Da) no enzyme desorption was detected below 150 mM NaCl. Optimal PEI-Sepabeads (prepared with PEI of 600 000 Da) was even much more thermostable than the covalent derivative prepared onto cyanogen bromide agarose. Moreover, this derivative presented a half-life 26-fold higher than that of the soluble enzyme at 45 degrees C, and the support could be reused 10 times after the full desorption of the enzyme without decreasing loading capacity.

[Study on the sorption and isolation of shikimic acid by 717 anion exchange resin]

OBJECTIVE

To establish a convenient, practical and environmental method for extracting and isolating shikimic acid.

METHODS

The content of shikimic acid was measured by RP-ion-pair HPLC, the effects of different pH, temperature, sample concentration and eluate concentration on 717 anion exchange resin were studied.

RESULTS

The yield of shikimic acid was 96.52% on the condition of 22 degrees C, pH > 6.5, 7.5 mg /ml sample concentration and 0.03 mol/L HCl eluting.

CONCLUSION

This method is feasible and suitable for the extraction and isolation of shikimic acid.

Retention controlling and peak shape simulation in anion chromatography using multiple equilibrium model and stochastic theory

The stochastic theory of chromatography and an equilibrium based approach were used for the prediction of peak shape and retention data of anions. This attempt incorporating the potential advantages of two different chromatographic phenomena for analytical purposes. It is an integrated method to estimate kinetic and thermodynamic properties for the same chromatographic run of ions. The stochastic parameters of eluted anions, such as the residence time of the molecule on the surface of the stationary phase, and the average number of adsorption steps were determined on the basis of a retention database of organic and inorganic anions (formate, chloride, bromide, nitrate, sulphate, oxalate, phosphate) obtained by using carbonate/bicarbonate eluent system at different pHs (9-11) and concentrations (7-13 mM). In the investigated IC system the residence times are much higher and the average number of sorption steps is somewhat smaller than in RP-HPLC. The simultaneous application of the stochastic and the multispecies eluent/analyte model was utilized to peak shape simulation and the retention controlling of various anions under elution conditions of practical importance. The similarities between the measured and the calculated chromatograms indicates the predictive and simulation power of the combined application of the stochastic theory and the multiple species eluent/analyte retention model.

Formation of aqueous MgUO2(CO3)3(2-) complex and uranium anion exchange mechanism onto an exchange resin

The formation of and stability constants for aqueous Mg-UO2-CO3 complexes were determined using an anion exchange method. Magnesium concentration was varied (up to 20 mmol/L) at constant ionic strength (I = 0.101, 0.202, 0.304, 0.406, and 0.509 mol/kg NaNO3), pH 8.1, total [U(VI)] = 10.4 micromol/L under equilibrium with atmospheric CO2. The results indicate that only the MgUO2(CO3)3(2-) complex is formed. The cumulative formation constant extrapolated to zero ionic strength is similar regardless of the activity correction convention used: logbeta113(0) = 25.8 +/- 0.5 using the Davies equation and = 25.02 +/- 0.08 using specific ion interaction theory (SIT). Uranium sorption onto the exchange resin decreased in the presence of Mg putatively due to the formation of MgUO2(CO3)3(2-) that had a lower affinity for the resin than UO2(CO3)3(4-). Uranium sorption results are consistent with an equivalent anion exchange reaction between NO3- and UO2(CO3)3(4-) species to retain charge neutrality regardless of Mg concentration. No Mg was associated with the anion exchange resin indicating that the MgUO2(CO3)3(2-) complex did not sorb.

Development of a two-step chromatography procedure that allows the purification of a high-purity anti-histone H1 monoclonal immunoglobulin M antibody with immunosuppressant activity

In organ transplantation, the development of a novel immunosuppressant free of the need for permanent administration and any serious side effects has eagerly been awaited. We have previously reported that an anti-histone H1 polyclonal antibody has immunosuppressant activity. Here we prepared an anti-histone H1 monoclonal antibody as an analytical tool to elucidate its mechanism of immunosuppression. The isotype of this monoclonal antibody was immunoglobulin M. A monoclonal antibody prepared for administration to organ transplantation model animals should not contain any allogenic proteins and should have high purity. Therefore, we conducted a two-step chromatography procedure, consisting of strong anion-exchange chromatography and gel filtration chromatography, to purify an anti-histone H1 monoclonal immunoglobulin M antibody from the serum-free culture supernatant of hybridomas. Consequently, we successfully purified the monoclonal antibody at 96%, a purification rate at which its administration to organ transplantation model animals is possible.

Stoichiometry of removal of natural organic matter by ion exchange

Five anion exchange resins, including a magnetic ion exchange (MIEX) resin, were evaluated for removal of Suwannee River Fulvic Acid (SRFA) in the presence of bicarbonate and chloride. The charge density of SRFA, obtained by potentiometric titration, was used to perform charge balances for ion exchange reactions involving SRFA, bicarbonate, and chloride under different solution conditions. The results clearly show the equivalence of SRFA uptake and chloride release by ion exchange. Although the structure of the anion exchange resins did not affect the stoichiometry of the reaction, the polyacrylic resins did exhibit greater removal of SRFA than the polystyrene resins. The hindered removal of SRFA by the polystyrene resins was hypothesized to be a result of size exclusion. The MIEX resin, which has a polyacrylic structure, performed similarly to the other polyacrylic resins. For the MIEX resin, the separation factor for SRFA over chloride was approximately 8 times greater than for bicarbonate over chloride. This work provides an improved understanding of the interactions between natural organic matter (NOM), inorganic anions, and anion exchange resins, and should result in more effective applications of ion exchange for the removal of NOM in the treatment of drinking water.

Selection of anionic exchange resins for removal of natural organic matter (NOM) fractions

Early elimination of natural organic matter (NOM) by ion exchange (IEX) in water treatment is expected to improve subsequent water treatment processes and the final drinking water quality. Nine anionic exchange resins were investigated to remove NOM and specific NOM fractions determined by liquid chromatography in combination with organic carbon detection (LC-OCD) and fluorescence excitation-emission matrices (EEM). Breakthrough of NOM was predicted by model calculations using Freundlich isotherms and IEX rate experiments. The time to breakthrough varied from 4 to 38 days. Removal of specific NOM fractions proved to vary considerably for the different types of IEX resins, ranging from 1% to almost 60%. The removal of NOM fractions, specifically humic substances, increased with an increase in water content of the investigated IEX resins and with a decrease in resin size. The best-performing IEX resins consisted of the smallest resins and/or those with the highest water content. The worst-performing IEX resins reflected the highest exchanging capacities and the lowest water contents.

Enriching basic and acidic rat brain proteins with ion exchange mini spin columns before two-dimensional gel electrophoresis

Proteome analysis by two-dimensional gel electrophoresis (2-DGE) faces significant challenges because of the complexity of biological samples. However, the complexity of a protein sample can be reduced prior to 2-DGE by applying protein fractionation. Protein fractionation allows analysis of one protein subset at a time, thereby, increasing the load of proteins of interest, enriching low-abundance proteins, and increasing the resolution of protein spots on a 2-D gel. Here we describe an ion exchange chromatography based method--the use of anion or cation exchange (AEX or CEX) mini spin columns--for sample fractionation. Using rat brain tissues, we demonstrate that these mini spin columns provide an easy, convenient, and reproducible way of fractionating brain proteins to enrich basic or acidic proteins before 2-DGE.

Experimental and theoretical study of anion-exchange preparative chromatography for neptunium: the first application to thorium(IV) and its equilibrium and kinetics

In order to study equilibrium and kinetic parameters in anion-exchange chromatography for preparatory purpose, a quantitative model for nonlinear anion-exchange chromatography in porous media was constructed, by paying special attention to interstitial length along void structure (cm) distinguished from apparent length (cm*). Langmuir-type adsorption isotherm for thorium(IV), as a natural substitution for neptunium(IV), in 6 mol dm(-3) nitric acid to anion-exchanger MSA-1 (200-400 mesh) was investigated in batch-wise and chromatographic experiments. The equilibrium parameters determined by batch-wise experiments determined as k=2.4x10(2) mol(-1) dm3 s(-1) and s0=0.5 mol dm(-3) agrees very well with the values of k=222 mol(-1) dm3 s(-1) and s0=0.5 mol dm(-3) derived from fitting by the numerical calculation. Kinetic parameters of ks and D affect band profile similarly, thereby maximum value of each parameter was evaluated as ks=1.3 mol(-1) dm3 s(-1) and D=9x10(-4) cm2 s(-1) by the numerical calculations.

Preparation and characterization of manganese dioxide impregnated resin for radionuclide pre-concentration

An easy and reproducible preparation of manganese dioxide impregnated resin of homogeneous particles has been described. The characteristics of radium, thorium, uranium and plutonium uptake (pH dependency, kinetic studies and matrix dependency) have been determined in batch mode. The resin due to its high efficiency for radium, uranium and thorium at neutral pH values can be an effective tool for radionuclide pre-concentration from liquid samples even with high dissolved solid content.

Factors affecting selectivity during dissolved organic matter removal by anion-exchange resins

Anion-exchange processes have received increased attention in recent years as efficient alternatives for removing disinfection byproduct precursors. In this research the preferential uptake of different dissolved organic matter (DOM) components, and hence the resulting reactivity after treatment, is shown to depend on the initial molecular weight (MW) distribution and the sulfate concentration. MW distribution is important because size-exclusion phenomena can occur in ion-exchange sorption, leading to the preferential uptake of low (ca. 1000 Da) MW species. Sulfate competition can reverse resin preference for low-MW species. DOM components that compete best with sulfate combine ionogenic group affinity and entropy-assisted adsorption. Entropy-assisted sorption, whereby sorption is promoted by the entropy gained from the desolvation of hydrophobic DOM moieties, is shown to be significant for two surface water sources. Entropic contributions are most significant when resin dosages are low and competition between DOM components and between DOM and sulfate are high. DOM components having MW near 1 kDa are sufficiently large to have significant hydrophobic moieties to promote entropy-assisted sorption and sufficiently small to enable access to exchange sites. Total uptake and preferential removal of specific UV absorbance (SUVA), an indicator of DOM reactivity, will thus depend on the initial MW distribution, how SUVA depends on MW, and the sulfate concentration.

Influence of anionic species on uranium separation from acid mine water using strong base resins

The presence of uranium and other elements in high concentrations in acid mine drainage at Poços de Caldas Uranium Mine (Brazil) is a matter of concern. The acid water pH is around 2.7, the uranium concentration is in the range of 6-14 mg L(-1), sulfate concentration near 1400 mg L(-1), fluoride 140 mg L(-1) and iron 180 mg L(-1). In this solution, where sulfate is present in elevated concentrations, uranium is basically in the form of UO(2)(SO(4))(3)(4-). This study investigated the separation of uranium from the other anions present in the acid water under batch and column mode using ion exchange technique. The pH studied was 2.7 and 3.9. Two strong base anionic resins were tested. The influence of ions, commonly found in acid waters like sulfate and fluoride, on ion exchange process was also assessed. Equilibrium studies were carried out to determine the maximum adsorption capacities of the resins. The resins showed a significant capacity for uranium uptake which varied from 66 to 108 mg g(-1) for IRA 910U and 53 to 79 mg g(-1) for Dowex A. The results also showed that SO(4)(2-) is the most interfering ion and it had a deleterious effect on the recovery in the pH range studied. Fluoride did not affect uranium removal.

Anion exchange fractionation of serum proteins versus albumin elimination

Elimination of albumin, constituting more than 50% of total serum proteins, allows increased protein loads on immobilized pH gradient (IPG) gels and better visualization of low-abundance proteins; however, it may result in the loss of albumin-bound low-abundance proteins. In this study, we report the prefractionation of serum proteins by batch anion exchange chromatography into three fractions: one containing proteins with isoelectric points (pI values) higher than the pI of albumin, a second fraction containing proteins with pI values in the same range as the pI of albumin, and a third fraction containing proteins with pI values lower than the pI of albumin. This procedure uses common instrumentation, is carried out under denaturing conditions, and takes less than 30min. We also report the loss of a clinically established prostate cancer serum biomarker, prostate-specific antigen (PSA), after albumin is eliminated using two commercially available albumin elimination kits: one that uses Cibacron Blue F3GA, which achieves albumin depletion through dye-ligand binding, and one that uses specific albumin antibody. The loss of PSA secondary to albumin elimination exceeded that after batch anion exchange serum sample prefractionation.

Comparison of chromatographic ion-exchange resins

A comparative study on weak anion exchangers was performed to investigate the pH dependence, binding strength, particle size distribution, and static and dynamic capacity of the chromatographic resins. The resins tested included: DEAE Sepharose FF, Poros 50 D, Fractogel EMD DEAE (M), MacroPrep DEAE Support, DEAE Ceramic HyperD 20, and Toyopearl DEAE 650 M. Testing was performed with five different model proteins: Anti-FVII mAb (immunoglobulin G), aprotinin, bovine serum albumin (BSA), Lipolase (Novozymes), and myoglobin. Retention showed an expected increasing trend as a function of pH for proteins with low pI. A decrease in retention was observed for some resins at pH 9 likely due to initiation of deprotonation of the weak anion-exchange ligands. Expected particle size distribution was obtained for all resins compared to previous studies. Binding strength to weak anion-exchange resins as a function of ionic strength depends on the specific protein. Binding and elution at low salt concentration may be performed with Toyopearl DEAE 650 M, while binding and elution at high salt concentration may be performed with MacroPrep DEAE Support. Highest binding capacities were generally obtained with Poros 50 D followed by DEAE Ceramic HyperD 20. A general good agreement was obtained between this study and data obtained by the suppliers. Verification of binding strength trends with model proteins was achieved with human growth hormone (hGH) and a hGH variant on the same resins with different elution salts, sodium chloride, sodium hydrogenphosphate, sodium sulphate, and sodium acetate. Static capacity measurements obtained in the traditional experimental set-up were compared with high-throughput screening (HTS) technique experiments with reasonable agreement. Isotherm data obtained from HTS techniques and pulse experiments were successfully combined with mathematical modelling to simulate, develop and optimise the separation process of two model proteins, Lipolase and BSA. The data presented in this paper may be used for selection of resins for testing in process development.

Sevelamer and Other Anion-Exchange Resins in the Prevention and Treatment of Hyperphosphataemia in Chronic Renal Failure

Sevelamer, or more precisely 'sevelamer hydrochloride', is a weakly basic anion-exchange resin in the chloride form that was introduced in 1997 for the treatment of the hyperphosphataemia of patients with end-stage renal failure, usually those on long-term haemodialysis. The rationale for this therapy was that sevelamer would sequester phosphate within the gastrointestinal tract, so preventing its absorption and enhancing its faecal excretion. Over the succeeding years, large numbers of patients have been treated with sevelamer, and it has fulfilled expectations in helping to control the hyperphosphataemia of end-stage renal failure. However, it is only one of many anion-exchange resins that could be used for this purpose, some of which are currently available for clinical use and are much less costly than sevelamer. Theoretical considerations suggest that some of these other resins might be at least as efficient as sevelamer in sequestering phosphate in the gastrointestinal tract. Neither sevelamer, nor any of these other agents, has been submitted to a proper metabolic balance study to measure the amount of phosphate sequestered by the resin in the bowel, and without this information it is impossible to judge which is the ideal resin for this purpose.

Adsorption equilibrium of fructosyltransferase on a weak anion-exchange resin

The adsorption equilibrium of a glycoprotein, fructosyltransferase from Aureobasidium pullulans, on an anion-exchange resin, Sepabeads FP-DA activated with 0.1M NaOH, was investigated. The adsorption isotherms were determined at 20 degrees C in a phosphate-citrate buffer with pH 6.0 using the static method. Sodium chloride was used to adjust the ionic strength in the range from 0.0215 to 0.1215 mol dm(-3) which provided conditions varying from a weak effect of salt concentration on protein binding to its strong suppression. The equilibrium data were very well fitted by means of the steric mass-action model when the ion-exchange capacity of 290 mmol dm(-3) was obtained from independent frontal column experiments. The model fit provided the protein characteristic charge equal to 1.9, equilibrium constant 0.326, and steric factor 1.095 x 10(5).

pH-gradient ion-exchange chromatography: an analytical tool for design and optimization of protein separations

This work demonstrates that a highly linear, controllable and wide-ranged pH-gradient can be generated through an ion-exchange chromatography (IEC) column. Such a pH-gradient anion-exchange chromatography was evaluated with 17 model proteins and found that acidic (pI<6) and basic (pI>8) proteins elute roughly at their pI, whereas neutral proteins (pI 6-8) elute at pH 8-9 regardless their pI values. Because of the flat nature of protein titration curves from pH approximately 6 to approximately 9, neutral proteins indeed exhibit nearly zero net charge at pH approximately 9. The elution-pH in pH-gradient IEC or the titration curve, but not the pI, was identified as the key parameter for pH optimization of preparative IEC in a fast and rational way. The pH-gradient IEC was also applied and found to be an excellent analytical tool for the fractionation of crude protein mixtures.