Determination of unbiased selectivity coefficients using pulsed chronopotentiometric polymeric membrane ion sensors

A new procedure for the determination of selectivity coefficients of neutral carriers using pulsed chronopotentiometric ion selective sensors (pulstrodes) is established. Pulstrode membrane which lacks an ion-exchanger suppresses the zero current ion flux, allowing a Nernstian response slope for even highly discriminated ions. Unlike previously developed methods, unbiased selectivity remains unaltered even with the exposure to the primary ion solution for prolonged time. Studies with potassium-, silver-, and calcium-selective electrodes reveal that pulstrodes yield the same or slightly favorable unbiased selectivity coefficients than reported earlier. In contrast to alternative methods for the determination of unbiased selectivity, this technique offers a unique simplicity and reliability. Therefore the new procedure promises to be a valuable additional tool for the characterization of unbiased selectivity coefficients for the ISEs.     

Modeling of divalent/monovalent ion selectivity of ion-exchanger-based solvent polymeric membranes doped with coexchanger

It is shown that the addition of a coexchanger does not always improve the selectivity of an ion-selective electrode. As a model case, the selectivity toward divalent primary ions I2+ in the presence of monovalent interference J+ is numerically simulated for membranes based on ion-exchanger R- and doped with a coexchanger (ionic additive) S+. It is, for the first time, demonstrated that the addition of a coexchanger, together with a high mobility of ion-exchanger sites, may be either beneficial or harmful to selectivity. Accordingly, two distinctive representatives of systems, i.e., membrane/solution are discussed. The theory is illustrated with experimental data obtained from PVC membranes based on calcium bis(2ethylhexyl)-phosphate plasticized with tris(2ethylhexyl)phosphate and doped with tetradecylammonium. Electrodes with these membranes exhibit both types of selectivity behavior. Interference from lithium with a calcium response may be sufficiently decreased by the addition of tetradecylammonium, while the interference from potassium and cesium was increased in the doped membranes.     

Role of metal ion incorporation in ion exchange resin on the selectivity of fluoride

Indion FR 10 resin has sulphonic acid functional group (H(+) form) possesses appreciable defluoridation capacity (DC) and its DC has been enhanced by chemical modification into Na(+) and Al(3+) forms by loading respective metal ions in H(+) form of resin. The DCs of Na(+) and Al(3+) forms were found to be 445 and 478 mg F(-)/kg, respectively, whereas the DC of H(+) form is 265 mg F(-)/kg at 10 mg/L initial fluoride concentration. The nature and morphology of sorbents are characterized using FTIR and SEM analysis. The fluoride sorption was explained using the Freundlich, Langmuir and Redlich-Peterson isotherms and kinetic models. The calculated thermodynamic parameters such as DeltaG degrees, DeltaH degrees, DeltaS degrees and sticking probability (S(*)) explains the nature of sorption. Comparison was also made by the elution capacity of these resins in order to select a cost effective material. A field trial was carried out to test the suitability of the resins with fluoride water collected from a nearby fluoride-endemic area.     

半碳化离子交换纤维的制备及表征

利用硝酸氧化聚丙烯腈基半碳化纤维制备了一种新型的弱酸性阳离子交换纤维。利用Boehm滴定、反射红外、热重分析等手段表征了纤维表面的氧化性基团的含量、表面化学结构和热稳定性等性能，考察了纤维对金属离子的吸附性能。结果表明，该半碳化离子交换纤维有更高的热稳定性；其表面氧化性基团的含量达3．78mmovg；对铅、铜、镁离子的静态吸附量分别为25．3、8．2、4．5mg／g，表现出良好的离子交换与吸附性能。     

Thermally activated electrostatic injection of solvated ions by a track membrane interfaced vacuum feedthrough

Electromembrane ion sources are considered as potential techniques for direct mass spectrometric sampling from ambient conditions. Interfacing of a time-of-flight mass spectrometer by means of a poly(ethylene terephthalate) track membrane requires investigation of the thermally activated processes involved. In this study, we directly attempt substantiating an activation-like performance of such track membrane-mediated interfaces. A number of KCl/glycerol solution samples were tested. A wide range of fixed, externally applied, potential drops was covered. For the charge extraction processes studied, we observe and discuss an activation term, exp(-ΔF/k(B)T), with a free-energy barrier ΔF = ΔF(0) - ΔF(Φ). The potential drop-dependent ΔF(Φ), was found to be sensitive to the varying salt concentration.     

Spectroelectrochemical sensing based on multimode selectivity simultaneously achievable in a single device. 20. Detection of metal ions in different oxidation states

Spectroelectrochemical sensing a metal in two different oxidation states, both of which are weakly absorbing in the visible wavelength range, was demonstrated with ferrous and ferric ion. The sensor consisted of an indium tin oxide optically transparent electrode (ITO OTE) coated with a thin film of Nafion preloaded with the ligand 2,2'-bipyridine (bipy). Fe2+ in the sample partitioned into the film where it reacted with bipy to form Fe(bipy)3(2+), which absorbs strongly at 520 nm. The change in absorbance (DeltaA) at 520 nm associated with the accumulation of Fe(bipy)3(2+) complex in the film was measured by attenuated total reflectance spectroscopy and was proportional to the concentration of Fe2+ in the sample. Iron in the Fe3+ form can also be determined, but it has a more complex coordination chemistry involving formation of [Fe2(bipy)4O(H2O)2]4+ as well as Fe(bipy)3(3+) in the film. Fe3+ was detected indirectly by reducing the nonabsorbing Fe3+-bipy complexes that accumulated in the film to absorbing Fe(bipy)3(2+) and monitoring DeltaA at 520 nm. The effects of film thickness and ligand concentration in the film on sensor sensitivity and response time for Fe2+ were evaluated. Detection limits of 0.6 x 10(-6) M for Fe2+ and 2 x 10(-6) M for Fe3+ were obtained with 300 nm thick films after 30 min of exposure to a quiescent sample. Careful manipulation of the potential applied with simultaneous optical detection enables Fe2+ to be distinguished from Fe3+, which is the first step in developing a sensor for speciating the two oxidation states in a mixture.     

A thermodynamic study of the temperature-dependent elution order of cyclic alpha-amino acid enantiomers on a copper(II)-D-penicillamine chiral stationary phase

The reversal of the elution order of cyclic alpha-amino acid enantiomers as a function of the temperature on a copper(II)-N,S-dioctyl-D-penicillamine ligand-exchange column is described. The thermodynamic parameters accounting for the retention and the separation of analytes were determined by means of van't Hoff plots. The influence of different chromatographic conditions on these parameters was investigated, showing little effect of the Cu(II) concentration in the eluent but strong influence of the organic modifier content on the separation. Further, the pH of the mobile phase was found to be a determining factor for the retention of the analytes. Based on these findings, a separation mechanism is postulated comprising the importance of complex formation for primary docking at the stationary phase, while hydrophobic interactions are crucial for chiral discrimination.     

"Entropically driven" chiral separations in supercritical fluid chromatography. Confirmation of isoelution temperature and reversal of elution order

Chiral separations depend upon column efficiency and chiral selectivity. Supercritical fluid chromatography (SFC) has been shown to have pronounced advantages in chiral separations due to its enhanced column efficiency at normal flow rates. Examination of factors affecting selectivity in SFC is crucial to systematic chiral method development. Selectivity is a compromise between differences in enantiomeric binding enthalpy and disruptive entropic effects. Increased temperature will decrease the effect of differences in enantiomer binding enthalpy, eventually decreasing selectivity to a point where the enantiomers coelute. Extension of this thermodynamic theory predicts that further increases in temperature lead to selectivity values of less than 1.0, and elution order of the enantiomers reverses. In this region separations are said to be "entropically driven", and selectivity increases (decreases from 1.0) with temperature. Performing separations in this region is attractive because column efficiency is also expected to increase with temperature. Such entropically driven separations have been observed only in gas chromatography. Most data used to support the application of this theory in SFC have been generated at subcritical temperatures, while theory purports to predict behavior above the critical temperature (T(c)). This approach ignores the effects of traversing the critical temperature in SFC, which is known to have a variety of unpredictable consequences. Work presented here shows the effect of temperatures above T(c) on chromatographic behavior. Contrary to theory, capacity factors increase near T(c) and column efficiency declines. Use of pressures well above the critical pressure lessens these effects. In accordance with theory, selectivity does decrease with temperature through T(c) and isoelution temperatures and two instances of elution order reversal are observed here for the first time in SFC.     

Separation of rare-earth and transplutonium elements by displacement chromatography on S-957 phosphonic ion exchanger

Sorption of transplutonium (TPE) and rare-earth (REE) elements on Purolite®S-957 ion exchanger containing phosphonic acid and sulfo groups was studied. Rare-earth elements are efficiently sorbed from weakly acidic solutions (≤0.1 M HNO₃). An increase in the solution acidity and introduction of sodium ions into the sorption medium lead to a decrease in the sorption. With S-957 resin, REE and TPE were separated for the first time on a phosphorus-containing sorbent by displacement chromatography in the presence of DTPA (diethylenetriaminepentaacetic acid).     

Effects of silver and potassium ions on ion exchange in float glass

The variation of optical and mechanical properties in ion-exchanged glasses was investigated. Ion exchange was carried out in KNO₃, NaNO₃ melts and their mixed melts with AgNO₃. The glasses used were soda-lime-silicate glasses produced by the float process. In order to analyse the effects of ion exchange, colour variation for optical properties, bending strength, surface microhardness and softening point for mechanical properties, and resistivity for electrical properties, were measured. In the optical properties, silver ions play an important role in colouring, ion exchange in the mixed melt of KNO₃ and AgNO₃, and additional heat treatment in air made it possible to obtain a range of colours from yellow to reddish-brown. Bending strength was increased by five times over the values of the parent glasses, surface microhardness was increased about 50 kg mm^?2, and the softening point was increased linearly with the amount of ion exchange resulting from ion exchange in the KNO₃ melt, because the potassium ion plays a great role in strengthening in the mechanical properties. On the other hand, in the mixed melt of KNO₃ and AgNO₃, bending strength and surface microhardness were increased slightly in contrast with the KNO₃ melt, and the softening point decreased on increasing the amount of ion exchange.     

A Ho(III) potentiometric polymeric membrane sensor based on a new four dentate neutral ion carrier

In this research, we report a new Ho^3 +-PVC membrane electrode based on N-(4,5-dimethyl-2-(picolinamido)phenyl)picolinamide (H₂Me₂bpb) as a suitable ion carrier. Poly vinylchloride (PVC)-based membrane composed of H₂Me₂bpb with oleic acid (OA) as anionic additives, and o-nitrophenyloctyl ether (NPOE) as plasticized solvent mediator. The sensor exhibits a Nernstian slope of 20.1 ± 0.2 mV decade^? 1 over the concentration range of 1.0 × 10^? 6 to 1.0 × 1^? 2 mol L^? 1, and a detection limit of 5.0 × 10^? 7 mol L^? 1 of Ho^3 + ions. The potentiometric response of the sensor is independent of the solution pH in the range of 3.5–9.4. It has a very short response time, in the whole concentration range (< 10 s), and can be used for at least eight weeks. The proposed electrode shows a good selectivity towards Ho^3 + ions over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. To assess its analytical applicability the proposed Ho^3 + sensor was successfully applied as an indicator electrode in the titration of Ho^3 + ion solutions in certified reference materials, alloy samples and for the determination of the fluoride ion in two mouthwash preparations.     

Preparation of a novel potassium ion imprinted polymeric nanoparticles based on dicyclohexyl 18C6 for selective determination of K+ ion in different water samples

This work reports the first application of the ion imprinting technology for determination of potassium ion by precipitation polymerization method. Ion imprinted polymeric (IIP) nanoparticles were prepared by using dicyclohexyl 18C6 (DC18C6) as a K⁺ ion selective crown ether, in the acetonitrile–dimethylsulfoxide (3:1; v/v) mixture as porogen. The imprint potassium ion was removed from the polymeric matrix using 0.5 M HNO₃. The scanning electron microscopy (SEM) micrographs showed colloidal nanoparticles of 60–90 nm in diameter and slightly irregular in shape. The obtained ion-imprinted particles for K⁺ showed selective recognition with rapid adsorption and desorption processes. It was found that imprinting results in increased affinity of the material toward K⁺ ion over other competitor metal ions with the same charge and/or close ionic radius. The synthesized IIP nanobeads were shown to be promising for solid-phase extraction coupled with flame photometry for determination of trace K⁺ ion in different water samples.     

Generation of polymeric structures on a computer

Our simulations of mechanical and tribological behavior of polymeric materials rely on the creation of realistic materials on a computer. They follow previous work with one- and two-phase two-dimensional materials [9, 10, 11]. We now report a procedure of creation of three-dimensional polymers. Related issues are those of characterization in terms of the average chain length and the average end-to-end distance and also of visualization of the structures before, during and after a tribological or mechanical simulated "experiment." Electronic Publication     

Synthesis,characterization and ion exchange properties of zirconium(IV) tungstoiodophosphate,a new cation exchanger

Zirconium(IV) tungstoiodophosphate has been synthesized under a variety of conditions. The most chemically and thermally stable sample is prepared by adding a mixture of aqueous solutions of 0·5 mol L⁻¹ sodium tungstate, potassium iodate and 1 mol L⁻¹ orthophosphoric acid to aqueous solution of 0·1 mol L⁻¹ zirconium(IV) oxychloride. Its ion exchange capacity for Na⁺ and K⁺ was found to be 2·20 and 2·35 meq g⁻¹ dry exchanger, respectively. The material has been characterized on the basis of chemical composition, pH titration, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis. The effect on the exchange capacity of drying the exchanger at different temperatures has been studied. The analytical importance of the material has been established by quantitative separation of Pb²⁺ from other metal ions.     

Spectroelectrochemical sensing based on multimode selectivity simultaneously achievable in a single device. 2. Demonstration of selectivity in the presence of direct interferences

Three modes of selectivity based on charge-selective partitioning, electrolysis potential, and spectral absorption wavelength were demonstrated simultaneously in a new type of spectroelectrochemical sensor. Operation and performance of the three modes of selectivity for detection of analytes in the presence of direct interferences were investigated using binary mixture systems. These binary mixtures consisted of Fe(CN)(6)(3-) and Ru(bpy)(3)(2+) and of Fe(CN)(6)(4-) and Ru(CN)(6)(4)(-) in aqueous solutions. Results on the Fe(CN)(6)(3-)/Ru(bpy)(3)(2+) binary mixture showed that an anion-exchange coating consisting of PDMDAAC-SiO(2) [where PDMDAAC is poly(dimethyldiallylammonium chloride)] and a cation-exchange coating consisting of Nafion-SiO(2) can trap and preconcentrate analytes with charge selection. At the same time, such coatings exclude interferences carrying the same type of charge as that of the exchange sites in the sensor coating. Using the Fe(CN)(6)(4-)/Ru(CN)(6)(4-) binary mixture, the Fe(CN)(6)(4-) component can be selectively detected by restricting the modulation potential cycled to a range specific to the redox-active Fe(CN)(6)(4-) component and simultaneously monitoring the optical response at the overlapping wavelength of 420 nm. It was also shown that, when the wavelength for optical monitoring was chosen as 500 nm, which is specific to the Ru(CN)(6)(4-) component, interference from the Fe(CN)(6)(4-) component for spectroelectrochemical detection of Ru(CN)(6)(4-) was significantly suppressed, even though the cyclic modulation potential encompassed the redox range for the Fe(CN)(6)(4-) component.     

Adsorption mechanism of trivalent metal ions on chelating resins containing iminodiacetic Acid groups with reference to selectivity

The adsorption equilibria of seven trivalent metal ions (M(3+): Sc(3+), Y(3+), La(3+), Fe(3+), Al(3+), Ga(3+), and In(3+)) on chelating resins containing iminodiacetic acid groups (-LH(2)) were studied. Adsorption curves, measured under the conditions of metal ions in excess against chelating groups, directly indicated the metal-to-ligand ratio of the complexes formed in the resin phase. Iron and group 13 metal ions were adsorbed as (-L)(2)HM, while group 3 metal ions were adsorbed as (-L)(3)H(3)M and (-L)(2)HM. The adsorption constants for (-L)(2)HM found for all the metal ions were well correlated with the formation constants of iminodiacetate complexes in aqueous solutions. The actual adsorption of group 3 metal ions was significantly enhanced beyond that expected from this correlation because of the formation of (-L)(3)H(3)M. This is why the selectivity in the adsorption of trivalent metal ions differs from that in the complexation of iminodiacetate in aqueous solutions. The effects of anions and the number of iminodiacetic acid groups per unit weight of resins were also discussed.     

Dependence of ion selectivity on ordered orientation of neutral carriers in ion-sensing membranes based on thermotropic liquid crystals

Thermotropic liquid-crystalline compounds were applied as membrane materials (membrane solvent and neutral carrier) for neutral carrier-type ion sensors to investigate how the ordered arrangement of neutral carriers affects the property of the resulting ion sensors. Nematic, smectic, and cholesteric liquid-crystalline compounds were used as the membrane solvents and crown ether derivatives with a molecular structure similar to the liquid-crystalline solvent as the K+ neutral carriers. Polarized IR spectroscopy and X-ray diffraction experiments confirmed that the highly ordered arrangement of membrane components was retained in the liquid-crystal-based ion-sensing membranes containing a neutral carrier and a lipophilic salt. The ordered arrangement of neutral carriers in the liquid-crystalline membranes enhanced the ion selectivity significantly, probably due to the efficient cooperation of two adjacent crown ether moieties in the highly ordered and aggregated state.     

Simulations and modeling of radioactivity buildup due to corrosion products in ion exchanger and filters of a typical PWR

A set of coupled first-order differential equations have been developed to simulate the corrosion product activity in ion exchanger and filters of a typical pressurized water reactor (PWR). Computer program CPAIR-RC has been modified for the current study to include the effect of nonlinear acceleration of corrosion on corrosion product activities. Simulations for five corrosion products ⁵⁹Fe, ⁹⁹Mo, ⁵⁶Mn, ⁵⁸Co, and ⁶⁰Co have been carried out. Simulation results show that the activities due to ⁵⁹Fe, ⁹⁹Mo, and ⁵⁶Mn saturate within approximately 1000 h of reactor operation. However, the activities due to ⁵⁸Co and ⁶⁰Co keep on accumulating in the ion exchanger of PWR during this time. The activity buildup in the ion exchanger due to ⁵⁶Mn starts after 77 h of reactor operation. When flow rate perturbations are introduced by decreasing flow rate to 40% of rated value, the activity due to ⁵⁶Mn saturates at the value of 1.27 × 10⁻³ μCi cm⁻³. For the case of nonlinearly acceelerating corrosion with a pump coast down, the activity for ⁵⁹Fe shows an initial drop with a decrease in flow rates. The activity drops from 2.37 × 10⁻² to 2.33 × 10⁻² μCi cm⁻³ before the reactor scram. The corrosion product activities calculated by the CPAIR-RC program are compared with some of the experimental data available in literature and show fair agreement. Published in Russian in Radiokhimiya, 2009, Vol. 51, No. 1, pp. 40–46. The test was submitted by the authors in English.     

Studies on separation of Cs/Ba and Zn/Cu binary mixtures on zirconium antimonate as ion exchanger

Zirconium antimonate (ZrSb) ion exchanger was prepared. Distribution coefficients of metal ions on ZrSb ion exchanger in solutions of various acids (hydrochloric, nitric, acetic, citric, ascorbic) and salts (sodium chloride and sodium nitrate) were determined to evaluate the ion exchange behavior and selectivity to specific ions. ZrSb, as compared to other inorganic ion exchangers, showed increased thermal and chemical stability. ZrSb is an efficient and promising ion exchanger for preparation of ¹³⁷Cs/^137m Ba and ⁶²Zn/⁶²Cu radioisotope generators.     

A new hybrid ion exchanger: Effect of system parameters on the adsorption of vanadium (V)

The hybrid ion exchanger consisted of PONF-g-GMA anion fibrous exchanger and IRA-96 bead-type anion exchanger was developed by combining different types of layers with hot-melt adhesive. Its ion exchange capacity and the pressure drop with flow rate of water were measured and the adsorption of vanadium (V) ions on the hybrid ion exchanger was evaluated with various process parameters such as pH, initial concentration, and temperature. It was observed that the adsorption kinetics of vanadium (V) ions on the hybrid ion exchanger could be analyzed with pseudo-second-order model.