Ion Exchange Distribution Research Articles

Optimization of the separation of enantiomers of basic drugs retention mechanisms and dynamic modification of the chiral bonding properties on a α1-acid glycoprotein column

The chromatographic properties of 29 basic drugs were studied by varying the pH and the concentration of inorganic ions in the mobile phase. It was observed that the chromatographic performance of most hydrophobic basic drug compounds could be strongly enhanced by decreasing the pH in the mobile phase from 7 to 4–6. The enantioselectivity increased and a much faster resolution was obtained. The results indicate that ion exchange and ion-pair distribution may be involved in the retention process of cationic enantiomers. Increasing the concentration of acetate and phosphate increases the retention of the enantiomers of the drug compounds. The relative contribution of the two retention processes can be affected by the pH and the nature and the concentration of the ions in the mobile phase. Decreasing the pH reduces the influence of the ion-exchange process since the negative charge of the protein is decreased. The enantioselectivity is also greatly affected by increasing salt concentration.

Synthetic, analytical and kinetic studies on a crystalline and thermally stable phase of antimony(V) arsenosilicate cation exchanger

A new, thermally stable and crystalline phase of antimony(V) arsenosilicate has been synthesized and characterized using X-ray, IR, TGA and DTA studies in addition to ion exchange studies such as determination of ion exchange capacity, elution, pH titration and distribution behaviour. On the basis of the distribution behaviour the material has been found to be highly selective for iron. Some binary separations of metal ions such as Sr(II)Cd(II) and Mn(II)Cd(II) have also been performed on a column of this material. The X-ray studies reveal the crystalline nature of the material, indicating a cubic structure. The kinetics of exchange for the metal ions has also been studied and some physical parameters such as the self-diffusion coefficient D 0, energy E a and entropy ΔS* of activation have been determined.

The binding of strontium and europium by an aquatic fulvic acid—ion exchange distribution and ultrafiltration studies

The complexation of an aquatic fulvic acid, FA, with Sr 2+ and Eu 3+ was studied at 0.10 and O1.O1 M NaClO 4 using trace levels of metal ([Sr 2+] = 10 −9 M and [Eu 3+] = 10 −11 M) and a constant FA concentration (0.12 g/l) by an ultrafiltration technique (UF) and an ion exchange distribution method (IEDS). The overall complex formation function, β OV for the two metals was calculated and its dependence on pH, ionic strength and method was investigated. The absolute value of log β OV, the pH dependence and the influence of the ionic strength on the complexation differed depending on the metal ion and experimental technique employed. By considering the functional group heterogeneity of the FA molecule, it was possible to predict the most predominantly bound site (keto—enol) and resolve the complex formation function for this site and EU 3+ (IEDS: 9.43 ± 0.29 l/eq at 0.10 M and 10.58 ± 0.72 l/eq at 0.01 M; UF: 7.19 ± 1.51 l/eq at 0.01 M and 6.88 ± 0.91 l/eq at 0.01 M). The results are discussed in the light of possible intrinsic problems of the two experimental methods.

Heterogeneity as a concept in the interpretation of metal ion binding by humic substances. The binding of zinc by an aquatic fulvic acid

Zinc binding by a well characterized fulvic acid was studied by the ion-exchange distribution technique and ultrafiltration method at 0.100 M NaClO 4 using trace amounts of zinc (≤ 10 −1 M) and two different fulvic acid concentrations (6.2 × 10 −4 and 1.2 × 10 −3 M). The results were interpreted by considering the various acidic sites envisaged from potentiometric titrations in aqueous and non-aqueous media. In addition to calculating the overall complex formation function, literature-based constants for the complexation between the metal ion and the ascribed functional group were employed to account for the observed binding patterns as a function of pH. This supported the interpretation of the functional groups assigned to the envisaged acidic sites. Results from the ultrafiltration method were in agreement with those obtained from the ion-exchange distribution technique.

Europium binding by an aquatic fulvic acid. Interaction functions for the “average” sites in the fulvic acid molecule

The interaction of a well characterized aquatic fulvic acid, Bersbo FA, with Eu 3+ has been studied using ion-exchange distribution studies and an ultrafiltration method. The results indicate that values of overall stability constants, Q MFA, obtained in the ion-exchange distribution studies (log Q MFA = 6.00–8.55), which increased with increasing pH, were higher by as much as two to four orders of magnitude than those obtained using the ultrafiltration technique (log Q MFA ≅ 5.10), and which were insensitive to changes in pH. Formation constants for the complexation of Eu 3+ by the various acidic moieties identified in the fulvic acid have been resolved by an iterative procedure taking into consideration the contribution due to separate phase effects. The environmental implications of the studies are discussed.

Electrochemistry of Yb 3+ and Eu 3+ at Nafion modified electrodes

The influence of the electrodeposition of a thin mercury film on the voltammetric behaviour of Yb 3+ and Eu 3+ incorporated by ion-exchange in Nation ® coated glassy carbon electrodes is examined. A significant role of the nature of the electrode material is observed only in the case of Yb 3+ and the improvement in the reversibility and reproducibility of the voltammograms observed after mercury deposition is attributed to the higher overpotential required for hydrogen evolution on mercury. No such effect is observed in fact in the case of Eu 3+, which is reduced at far less negative potential values than Yb 3+ and, in this case, reversible and reproducible voltammetric patterns are obtained at both modified electrodes. The detailed analysis of the ion-exchange process demonstrates that mercury deposition does not cause deterioration of the ion-exchange properties of the Nation coating, while the nature of the supporting electrolyte cations examined (Li +, Na +, K +, Rb +, NH + 4, tetraethylammonium) proves to influence significantly both the extent and rate of incorporation. The ion-exchange distribution and selectivity coefficients of Nation for the two rare earth cations studied are also reported together with the relevant apparent diffusion coefficients.

The binding of cadmium by an aquatic fulvic acid: A comparison of ultrafiltration with ion-exchange distribution and ion-selective electrode techniques

An ultrafiltration technique has been adapted to obtain information on the binding of cadmium by a fulvic acid extracted from a deep groundwater. The results obtained are compared to those obtained by the ion-exchange distribution method (Schubert's approach) and an ion selective electrode method. The data obtained have been analyzed taking into consideration the heterogeneity of the fulvic acid sample. Results from the comparison indicate that with a proper design and conditioning of the diaflo membrane, the ultrafiltration technique offers a promising approach with respect to obtaining meaningful information on the binding of trace metals by natural organic acids.

Inorganic ion-exchangers for the removal of zirconium, hafnium and niobium radioisotopes from aqueous solutions

Studies were made on the uptake of zirconium, hafnium and niobium isotopes onto zeolites and amorphous zirconium phosphate. Ion exchange capacities and distribution coefficients were determined and the influence of pH examined. Kinetic experiments were made to determine the rates of uptake of the radioisotopes on the exchangers and to measure the leaching of isotopes from preloaded exchangers by synthetic sea water, simulated pond water and distilled water.

Complex-forming properties of natural organic acids: Fulvic acid complexes with cobalt, zinc and europium

The complex-forming properties of a fulvic acid sample have been studied by an ion-exchange distribution method. The results have been analysed by a novel physicochemical approach which attempts to take into account complications introduced by the polyelectrolyte nature and functional heterogeneity of the fulvic acid molecule. These studies with trace level concentrations of cobalt, zinc and europium show that these metal ions are selectively complexed by the weakly acidic enol grouping of the fulvic acid molecule. The logarithms of the stability constants (β 1) for the cobalt, zinc and europium chelates are 6.5, 6.4 and 10.3 respectively.

Ion exchange studies of U(VI), Th(IV), Pu(IV) and Eu(III) on a macroreticular resin in TBP-Shell Sol-T solutions

Ion exchange studies of uranium(VI), thorium(IV), plutonium(IV) and europium(III) ions on a macroreticular cation exchange resin, Amberlyst A-15, from solutions of 30% and 5% TBP—Shell Sol-T have been carried out. The metal ions were extracted into TBP Shell Sol-T phase from 8M NH4NO3 at different nitric acid concentrations. Ion exchange distribution ratios as a function of organic phase acidity of 30% and 5% TBP have been computed. Separation factors computed from the observed Kd values are plotted as a function of organic phase acidity.

Synthesis, ion exchange behaviour and characterization of chromium(III) arsenosilicate cation exchanger

Chromium (III) arsenosilicate, a new cation exchanger has been synthesized. Its characterization has been made using X-ray, IR and TGA methods. The chemical composition, ion exchange capacity, elution curve, concentration curve, pH titrations and distribution studies have also been done in order to establish its chemical behaviour as an ion exchanger.

Cation-exchange behaviour of the platinum group and some other rare elements in hydrobromic acid-thiourea-acetone media

Ion-exchange distribution coefficients and elution curves are presented for copper(I), silver, gold(I), palladium, platinum(II), rhodium(III), iridium(III), ruthenium(III), osmium(III), mercury(II), thallium(I), tellurium(II), lead and bismuth in mixtures of thiourea, hydrobromic acid, acetone and water, with the cation-exchange resin AGW50W-X4. The system affords excellent separations of rhodium, mercury, silver (or copper), tellurium, gold, and palladium (or platinum) from each other.

Cation-exchange in thiourea-hydrochloric acid solutions

Ion-exchange distribution coefficients are reported for several transition and post-transition elements in solutions of hydrochloric acid (0.1–3.0 M) and thiourea on AG50W resins. Some typical elution curves illustrate use of the systems with special reference to the separation of small amounts of gold, palladium, platinum, rhodium and iridium from large amounts of numerous base metals by using 1.5 M hydrochloric acid-0.1 M thiourea as eluent. Also illustrated is the use of a bromine-containing solution to strip thiourea complexes from a cation-exchange column.

Cation-Exchange Study on a Crystalline and Thermally Stable Phase of Antimony Silicate. Effect of Irradiation on Ion-Exchange Behavior and Separation of Cd(II) from Zn(II) and Mn(II) and of Mg(II) from Ba(II), Ca(II), and Sr(II)

Abstract A systematic ion-exchange study has been performed on antimony silicate, which includes its ion-exchange capacity, elution behavior, pH titrations, and distribution coefficients of common metal ions. The Kd values for alkali metals vary with the pH of the solution and the material is found to be highly selective for Rb(I) at pH values greater than 1. On the basis of distribution studies, the separation of Cd(II) from Zn(II) and Mn(II) has been achieved. Similarly, Mg(II) has been separated from Ba(II), Ca(II), and Sr(II) to illustrate its utility. Antimony silicate is very stable both thermally and chemically and possesses reproducible ion-exchange properties; also, the effect of irradiation on the ion-exchange behavior is negligible. A tentative formula of the material has also been proposed based on chemical, infrared, and thermogravimetric analysis studies. The x-ray studies reveal that the exchanger is crystalline with a d-value of 6.09 A.

Equilibration studies of an inorganic ion exchange material with liquid nuclear waste simulant using radiotracer techniques

Ion exchange distribution coefficients of zirconium, ruthenium, europium, and strontium, elements found in high level nuclear waste, were determined for a new titanium hydrous oxide-type inorganic ion exchange compound. Coefficients were determined at ambient temperatures and at 85°C. The equilibrations were done in solutions simulating the composition of nuclear waste expected from the Allied-General Nuclear services, Barnwell. South Carolina plant. The progress of each reaction was monitored by adding a radiotracer of the element investigated to the simulated waste solution. Ambient temperature distribution coefficients ranging from a high of 1.2·106 for Zr to a low of 58 for Eu were obtained when equal weights of ion exchange material were used. Significantly higher distribution coefficients were found at 85°C than at ambient temperatures.

Countercurrent elution of uranium(IV) and iron(III) from an anion-exchange resin

A countercurrent elution method for the separation of uranium and iron has been developed. The separation is based on changing the solution composition along the anion-exchange column and on the difference in the stability constants and the ion-exchange distribution coefficients of the sulphate complexes of uranium and iron.

ChemInform Abstract: ION‐EXCHANGE EVIDENCE FOR THE POLYNUCLEAR ION TRIS‐(HYDROXOBERYLLIUM(II))

AbstractDie Ionenaustauschverteilungsmethode zur Messung von Ionenladungen wird zur Anwendung für in hoher Konzentration vorliegende unbekannte Ionen modifiziert.

Ion-exchange evidence for the polynuclear ion tris[hydroxoberyllium(II)

The original ion-exchange distribution method for measuring ionic charge, limited to species present at low concentration relative to a reference ion, has been modified for use with high concentrations of the unknown ion. Limitations of this ‘inverse’ method have been assessed by measuring the charges of a number of well known ions. A beryllium hydrolysis polymer has been characterized in dilute perchlorate solutions effectively free from other electrolytes. In these slightly acid solutions (pH 5·5) the predominant polymeric species has a charge of +3 and a ‘metal atom-to-charge ratio’ of one. This identifies the ion as the trimer [Be3(OH)3]3+, originally proposed by Kakihana and Sillen on the basis of potentiometric evidence.

Absorption spectra and composition of complexes sorbed in ion exchangers—I The copper(II)-chloride complex system

The absorption spectra of copper(II)-chloride complexes adsorbed on anion-exchange resins of various degrees of crosslinking from a solution in 6 M hydrochloric acid and different copper concentrations have been observed. The composition of those complexes giving particular spectral patterns in the resin phase has been investigated by ion-exchange distribution measurements. At low copper concentrations or low degrees of crosslinking of the resin, a monomeric chlorocomplex (CuCl 3 −) was predominant. A binuclear complex (Cu 2Cl 7 3−) with a chloride ion bridge was gradually produced at higher concentrations of copper or higher degrees of crosslinking of the resin. Thus the following equilibrium may occur in the resin phase. 2 CuCl 3 − + Cl − ⇌ Cu 2Cl 7 3−. The validity of ion-exchange methods employed in this work was confirmed by experiments with chlorocomplexes of iron(III) and cobalt(II) whose compositions in the resin phase are known.

Investigation of the tantalum fluoride system using the fluoride-selective electrode

Stability quotients for mono- through heptafluorotantalates in 2 M perchlorate at 25°C were calculated from measurements of free fluoride ion concentrations by the lanthanum fluoride membrane electrode. Ion exchange distribution measurements indicate that anionic fluoride complexes exist below n = 5 .