Ion-exchange Constants Research Articles

Mechanism of retention of acidic solutes by octadecyl silica using quaternary ammonium pairing ions as ion exchangers

The adsorption isotherms of four commonly used quaternary ammonium pairing ions in aqueous solution on ODS Hypersil are reported. The capacity factors of four substituted benzoic acids as test solutes are measured as a function of pairing ion concentration under conditions of complete solute ionisation. The chromatographic behaviour of an undissociated solute, 5-hydroxymethylfurfuraldehyde, is also examined under these conditions. Over the wide range of pairing-ion concentrations used, maximum values of capacity factors are observed. A mechanism of retention, combining desolvation and ion exchange, which considers the effect of adsorbed pairing ion on surface available for desolvation is proposed. On the basis of this mechanism an equation relating capacity factor and adsorbed pairing-ion concentration is derived. The data obtained in this investigation are fitted to the equation and the desolvation and ion-exchange constants are estimated. The behaviour of the neutral solute 5-hydroxymethylfurfuraldehyde is examined in the light of the derived equation.

Potentiometric properties of trialkylammonium ion-exchangers

The potentiometric behaviour of nitrobenzene solutions of 21 trialkylammonium salts employed as membrane material has been investigated. Deviations from ideal Nernst response curves for chloride, bromide, iodide, and perchlorate sensors were explicable on the basis of partition and hydrolysis of the ion exchangers. Interference coefficients for the anion selective electrochemical sensor tridodecylammonium perchlorate could be related to the ion-exchange constant of the salt.

Catalysis and inhibition of the alkaline hydrolysis of benzocaine and analogs by a cationic surfactant.

The first-order rate constants for the alkaline hydrolysis of ethyl benzoate and ethyl p-nitro- and p-aminobenzoates (benzocaine), catalyzed by CTAB, a cationic surfactant, were measured at 25°in the presence of sodium hydroxide and sodium bromide. Although the alkaline hydrolysis of esters is generally accelerated by cationic micelles, that of the three benzoates tended to be inhibited by CTAB micelles under the following conditions : (i) at high CTAB concentrations, (ii) at high concentrations of sodium hydroxide, (iii) at high concentrations of an added salt (including buffer components), (iv) at high ester concentrations, and (v) for compounds possessing a small value of the Hammett substituent constant. These effects were explained quantitatively on the basis of a theory in which the total counterion concentration is assumed to remain constant regardless of the concentrations of CTAB, sodium bromide, and sodium hydroxide, and in which the association constant for a CTAB micelle and an ester, the degree of counterion binding to CTAB micelles, the ion-exchange constant, and a relative rate constant are taken as parameters.

On the properties of solid and liquid ion exchangers—V: The potassium-hydrogen exchange on dinonylnaphthalene sulfonic acid in heptane in the temperature range 1–80°C

The potassium-hydrogen exchange on dinonylnaphthalene sulfonic acid dissolved in heptane has been studied in the temperature range 1–80°C using batch techniques and titrimetric analysis. The data can be fitted with a simple model, where it is assumed that the system contains three kinds of micelles, HDNNS-micelles. KDNNS-micelles and a mixed micelle (K. H)DNNS each with a different ion exchange constant. The relation between the experimental value for the equilibrium quotient (κ) and the three parameters κ 1, κ 2 and κ 3 is logκ= X logκ 1+{l− X} logκ 2+ X(l− X) logκ 3 where X is the mole fraction of potassium in the organic phase, i.e. the distribution of micelles is assumed to be statistical. From the curves log κ( 1 T ) x the function ΔH( X) is obtained at each temperature. These data can be fitted with the same model i.e. δH °=δH 1 ° X+δH 2 °(1− X)+δH 3 ° X(1− X) Together with the free energy data ( ΔG° = − RT ln κ) entropies are computed for the three kinds of micelles. It is found that while the two pure micelles have negative entropy changes, the mixed micelle has a positive entropy change, provided the assumptions inherent for the equation above are correct. The mixed micelle concept also explains the water extraction in the system HDNNS-KDNNS in heptane as shown for data at 25°C.

Specific factors involved in the spreading of chromatographic zones in ion-exchange complexing chromatography

Studies were made of the effect on the broadening of a chromatographic zone of changes in the slope of the sorption isotherm, caused by the changes in the process of separation, ion-exchange constants, pH of the solution and the composition and instability constants of complexes formed. It is demonstrated that complexing in a solution produces a pH gradient at the displacing ion-separated mixture interface, which results in a considerable broadening of the bandwidth of the displacing ion and in its penetration into the zone of separated elements. The last two characteristics depend on the pH gradient, the absolute value of the equilibrium pH in the zone of separated elements and the slope of the sorption isotherm of the displacing ion. The changes in the sorption isotherm of the displacing ion, observed in the process of transfer of this ion from the separated zone into the layer of free ion exchanger, depend on the cationic form of the layer of free ion exchanger and affect both the shape and the width of the zone of separated elements.

Determination of the true ion exchange constants and instability (dissociation) constants of their complexes, formed in the phase of the ion exchange resin, according to the dependence of the apparent exchange constants on the degree of coverage of the ion exchange resin

1. A method was proposed for finding the true exchange constants of ions (Ktrue) and the dissociation constants (Kdis) of their complexes, formed in the phase of the ion exchange resin, by graphical comparison of the calculated and experimental curves of the dependence of the apparent exchange constants (Kapp) of the investigated ions for the hydrogen ion on the degree of coverage of the ion exchange resin. 2. Tables were compiled and families of calculation curves constructed for the exchange of two ions at any values (Ktrue) and with broad variations of combinations (Kdis) and charges of the ions. As applied to the weakly acid carboxyl cation exchange resin KB-4P-2, the experimental curves for the exchange of alkali ions are in good agreement with the calculated curves, while those for ions of the alkaline earth metals are in satisfactory agreement. 3. The sequences of Ktrue in the series Cs+-Li+ and Ba2+-Mg2+ are close to those on strongly acid cation exchange resins. The numerical values of Ktrue proved to be three to five orders of magnitude greater than Kapp, but below the expected values. 4. The constant Kdis of the hydrogen ion is an order of magnitude greater than for carboxylic acid monomers.

Characteristics of novobiocin and chloride anion exchange on strongly basic anionites in aqueous-alcohol solutions

1. It was found that the selectivity of novobiocin ion adsorption from aqueous-alcoholic solutions on strongly basic anionites is much less than the selectivity of adsorption from aqueous solutions. 2. It has been shown that the selectivity of novobiocin ion adsorption increases with increase in the surface coverage by organic ions. 3. The dependence of the novobiocin and chloride ion-exchange constants on the percent content of ethanol in solution on structurally different sorbents is variable in nature.

Measurement of thermodynamic functions for the sorption of amino acids on sulfonic acid resins in the hydrogen form

1. Sorption of amino acids in acidic solutions on sulfonic acid resins having a low value for ion exchange constants was determined by enthalpy factors. 2. Sorption of amino acids as zwitter-ionsis completely controlled by changing the entropy of the system. 3. A marked effect of sorbent structure on sorption selectivity of zwitter-ions was not observed.

Ion exchange equilibria in the presence of organic solvents—I The influence of organic solvents on the distribution constant of praseodymium

A systematic study was made of the influence of the addition of organic solvents on the distribution coefficients of praseodymium between the resin KU 2 in H-, NH 4-, Na- and K-forms) and solutions containing HCl, organic solvent and H 2O. It was observed that the organic solvents do not influence the character of the reaction between cations and resin but only modify the value of the ion-exchange constants.