Counterion Selectivity Research Articles

Porous membrane controlled polymerization of nanofibers of polyaniline and its derivatives

A novel, simple, and scalable technique to control the formation of the nanofibers of polyaniline and its derivatives via porous membrane controlled polymerization (PMCP) is reported. Through appropriate synthesis conditions, there are nearly 100% nanofibers formed with diameters tunable from 20nm to 250nm via the selection of pore diameter, monomer, counterions, and polymerization conditions. The nanofiber lengths vary from sub-micrometre to several micrometres. A single nanofiber can be easily isolated from the agglomeration. X-Ray diffraction patterns show that doped polyaniline nanofibers are substantially crystalline.

Identification of chemically selective displacers using parallel batch screening experiments and quantitative structure efficacy relationship models.

Parallel batch screening experiments were carried out to examine how displacer chemistry and salt counterions affect the selectivity of batch protein displacements in anion exchange chromatographic systems. The results indicate that both salt type and displacer chemistry can have a significant impact on the amount of protein displaced. Importantly, the results indicate that, by changing the displacer, salt counterion, or both, one can induce significant selectivity changes in the relative displacement of two model proteins. This indicates that highly selective separations can be developed in ion exchange systems by the appropriate selection of displacer chemistry and salt counterion. The experimental batch screening data were also used in conjunction with various molecular descriptors to generate quantitative structure efficacy relationship (QSER) models based on a support vector machine feature selection and regression tool. The models resulted in good correlations and successful predictions for an external test set of displacers. A star plot approach was shown to be a powerful tool to aid in the interpretation of the QSER models. These results indicate that this modeling approach can be employed for the a priori prediction of displacer efficacy as well as for providing insight into displacer design and the selection of proper mobile-phase conditions for highly selective separations.

New Method for Estimating the Degree of Ionization and Counterion Selectivity of Cetyltrimethylammonium Halide Micelles: Chemical Trapping of Free Counterions by a Water Soluble Arenediazonium Ion

Products from spontaneous reaction of a short-chain, water soluble arenediazonium salt, 2,4,6-trimethylbenzenediazonium tetrafluoroborate (1-ArN2BF4), in aqueous micellar solutions of cetyltrimethylammonium halides ((CTA)X (X = Cl, Br)) are used to estimate the degree of ionization, α, and the ion exchange constant, KBr/Cl. The arenediazonium ion (1-ArN2+) reacts by rate-determining loss of N2 to give an aryl cation that traps available nucleophiles, i.e. H2O, Cl-, and Br-, to give stable phenol (1-ArOH) and halobenzene products (1-ArCl and 1-ArBr), respectively. Product yields are determined by HPLC from calibration curves obtained from independently prepared standards. Reproducible yields are obtained at very low halide ion concentrations, on the order of millimolar, well within the range needed to detect the “free counterions” in the aqueous intermicellar pseudophase. The basic assumption of the method is that 1-ArN2+ remains in the aqueous pseudophase at all (CTA)X and NaX concentrations. Trends in th...

Determination of lanthanum in monazite sand after selective solvent extraction separation of the picrate with dibenzo-[24]-crown-8

The solvent extraction of LaIII from picrate media was carried out with a dichloromethane solution containing large cavity size crown ethers (> 4A), namely dibenzo-[24]-crown-8 (DB24C8), dicyclohexano-[24]-crown-8 (DCH24C8) and dibenzo-[30]-crown-10 (DB30C10). It was found that LaIII was poorly extracted when DB30C10 was used, whereas both DB24C8 and DCH24C8 were good extractants. However, DB24C8 was preferred over DCH24C8 owing to its superior selectivity over the other lanthanides. The effects of variables such as solvent, counter ion concentration, pH, ligand concentration, equilibration time, stripping agent and selectivity over other elements were investigated. Under the optimized conditions, LaIII was quantitatively extracted from 0.0002 mol l–1 picric acid at pH 9 with 0.02 mol l–1 DB24C8 in dichloromethane. The extracted metal ion was stripped from the organic phase with 0.5 mol l–1 perchloric acid, and its concentration determined spectrophotometrically at 651.5 nm as its complex with Arsenazo III (pH, 3.2). A significant selectivity for LaIII over other lanthanides was observed. Replicate analysis of a monazite sand sample for lanthanum yielded results comparable to those obtained by atomic absorption spectrometry. The composition of the extracted species, viz., LaIII: DB24C8: picrate, was 1:1:3.

Counterion binding to poly(allylammonium) cation

AbstractChloride ion activity coefficients in aqueous solutions of poly(allylamine) hydrochloride (PAA · HCl) have been determined both in the absence and the presence of simple salts. Without added salt, the activity coefficient depends on the polymer concentration. With added salt, the binding of added counterions by PAAH+ is evaluated from the release of chloride ion. The extent of interaction between counterions and PAAH+ at a given polymer concentration decreases in the order SO ≫ ClO > NO > Cl− > Br− > I−. This order of counterion selectivity agrees with the previous estimation of potentiometric titrations. The result shows that the hydration of the counterion, as well as its charge, plays an important part in counterion binding to the polyion.

Theory of concentration polarization effects in electrodialysis on counter-ion selectivity of ion-exchange membranes with differing counter-ion distribution coefficients

This paper is concerned with the theory of the effect of concentration polarization under direct current upon the counter-ion selectivity of an ion-exchange electrodialysis membrane. The equilibrium selectivity is induced by the differing uptake of the counter-ions by the membrane, owing to the difference in their distribution coefficients between the membrane and solution phases.The numerical calculations are supplemented by an asymptotic analysis for a certain range of bulk concentrations and distribution coefficients, which provides an analytical expression for the dependence of selectivity on the electric current in the entire current range.

A new method for estimating counter-ion selectivity of a cationic association colloid: Trapping of interfacial chloride and bromide counter-ions by reaction with micellar bound aryldiazonium salts

Yields of aryl halides and phenolic products from dediazoniation of a hydrophobic aryldiazonium salt bound to cetyltrimethylammonium halide, CTAX, micelles in 0.1 to 0.2 M HX with added NaX(XCl − and Br −) are used to estimate, simultaneously, the quantity of halide counter-ions and water at the micelle surface. The interfacial counter-ion concentration increases, both in solutions of CTABr with added NaBr and CTACl with added NaCl with a proportionate decrease in interfacial water. The selectivity of CTAX micelles toward Br − and Cl − in solutions containing mixtures of the two ions is obtained directly, unlike all previous methods which require an estimate of the fraction of bound counter-ions. Counter-ion exchange constants, K Br Cl, estimated from aryl bromide/aryl chloride yield ratios at high NaX, are consistent with published values. Our results show, for the first time, that K Br Cl is insensitive to ionic strength up to 3.0 M NaX when [Br −]/[Cl −]=1.0, but has modest dependence on the mole fraction of Br − at constant total NaX. K Br Cl is also independent of surfactant concentration, after correcting for the fraction of bound counter-ions. In principle, product ratios from reaction of hydrophobic aryldiazonium salts can be used to estimate the relative concentrations of all nucleophiles at the surfaces of association colloids, provided stable aryl substituted products are formed via rate determining loss of N 2.

Isotachophoresis of proteins

The analytical separation of proteins by isotachophoresis (ITP) was achieved in a short electrophoretic path and with a resolution comparable to that of isoelectric focusing by the appropriate selection of (1) a mixture of ampholytes as spacers to generate linear gradients of electrophoretic mobility and (2) the counter ions chosen to buffer the complete pH gradient generated. This ITP technique is exemplified by the analysis of plasma proteins in agarose gels. Up to 46 samples in the same gel plate were analysed. The resolution was such that at least 30 clear and discrete bands per sample could be observed after staining with Coomassie Brilliant Blue. The resolving power of ITP could be further increased for the study of a particular protein or zone by the selection of suitable spacers and counter ions.

Counterion selectivity in cationic polyelectrolytes

AbstractChloride ion activity coefficients in aqueous solutions of several cationic copolymers have been determined using ion‐selective electrodes in both the absence and the presence of simple univalent and divalent salts. Without added salt, the activity coefficient depends on the polymer concentration. It increases with increasing concentration of the added salt. The extent of interaction between counterions and polyions at a given polymer concentration, as estimated form chloride anion activity, is greater for bivalent than for univalent anions. Experimental data are in good agreement with theory. Selective interaction of anions with the ammonium copolymers has also been evidenced by viscometry. The selectivity follows the order For organic anions, in addition to electrostatic interactions, hydrophobic effects, which depend on the structure of the copolymer, play a significant role.

Effect of concentration polarization upon the valency-induced counterion selectivity of ion-exchange membranes

The paper contains a theoretical study of the variation of steady-state membrane selectivity for counterions of different valencies in the course of concentration polarization. The computations show that the system loses most of its counterion selectivity before the concentration polarization results in a pronounced deviation from the linear ohmic voltage against current dependence. This is explained by the enhanced depletion of the Nernst layer of the preferred counterion, resulting in the relative inpoverishment of the membrane in the latter, under conditions at which the membrane still controls the counterion selectivity. At higher currents, when a strong concentration polarization sets in and the limiting stage of counterion transfer shifts to the Nernst layer, the selectivity is almost totally lost, except for a small residual effect, due to a different contribution of migration into the limiting ionic fluxes for species of different valencies.

Reversed-Phase, Ion-Pair Separation of L-Methionine and L-Methionine Dipeptides Complexed with Palladium (II)

Abstract A high performance liquid chromatographic (HPLC) method is described for separation of L-methionine and L- methionine dipeptides complexed with palladium (II). Under isocratic conditions, at room temperatures, with the appropriate selection of counter-ion (cetyltrimethylammonium or trioctylmethylammonium), it was possible by ion-pairing reversed phase chromatography to resolve the palladium (II) complexes studied. Stainless steel and polythylene columns were used. The chroma-tograms from both the two different materials made columns indicate about the same ratio of capacity factor of the palladium (II) complexes.