Electrochemical study of flunitrazepam partitioning into zwitterionic phospholipid monolayers

The effect of flunitrazepam (FNTZ) on molecular packing of distearoylphosphatidylcholine (DSPC) and distearoylphosphatidylethanolamine (DSPE) monolayers adsorbed at the water/1,2-dichloroethane interface was investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS).The interfacial packing of the monolayer was estimated by the analysis of the voltammetric transfer of tetraethylammonium cation (TEA⁺) from the aqueous to the organic phase in the presence of different cations (Li⁺, Ca²⁺ and K⁺) in water. An important blocking of the transfer process was observed in the case of DSPE monolayer when the aqueous phase contained Li⁺ and Ca²⁺cations indicating a highly ordered structure. FNTZ produced an enhancement of this blocking effect. EIS experiments evidenced the presence of different domains in the monolayer when FNTZ was present. The covered zones of the monolayer exhibited higher compactness compared with the corresponding in absence of FNTZ. TEA⁺ transfer process does not occur across so packed regions but through the very small uncovered zones (pores), resulting in a decrease of the transfer current. This blocking effect of DSPE monolayer containing FNTZ was not observed in the case of DSPC. It was concluded that FNTZ accumulation at the interface induces lateral interactions between DSPE molecules resulting in a highly condensed monolayer.     

Voltammetric study and surface pressure isotherms describing Flunitrazepam incorporation into a distearoylphosphatidic acid film adsorbed at air/water and water/1,2-dichloroethane interfaces

The effect of Flunitrazepam (FNTZ) on molecular packing of distearoylphosphatidic acid (DSPA) adsorbed at the air/water and the water/1, 2–dichloroethane interface was investigated using cyclic voltammetry (CV) and surface pressure–molecular area isotherm. FNTZ incorporation into the DSPA monolayer changes the state of the film. The results indicate that a structuring effect dependent on the pH and the cation present in the base aqueous electrolyte takes place, which leads to a decrease in the permeability of the film.     

Rapid Separation of Tl+ and Pb2+ from Various Binary Cation Mixtures Using Dicyclohexano-18-crown-6 Incorporated into Emulsion Membranes

Abstract

Relative transport rates of metal cation nitrates (Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Tl⁺, Ca²⁺, Sr²⁺, Ba²⁺, and Pb²⁺) in a water-toluene-water emulsion membrane system were measured. The toluene component contained the surfactant Span 80 and the crown ether dicyclohexano-18-crown-6. The aqueous receiving phase contained Li₄P2O₇. When each metal cation was individually present in the aqueous source phase, metal extraction was complete within 10 min with the order of extraction being Tl⁺ > Cs⁺ > Ag⁺ > Rb⁺ > K⁺ ≥m Na⁺ and Pb⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺ for uni-and bivalent cations, respectively. Significant extraction was found for all cations except Na⁺, K⁺, and Ba²⁺. Some metal ions were concentrated nearly 10-fold in a 10-min period. Relative transport rates were determined when binary cation mixtures of either Tl⁺ or Pb²⁺ were present at equal concentrations with each of the remaining metal ions in the source phase. Tl⁺, when present with either Na⁺, Cs⁺, or Rb⁺, was selectively extracted from the source phase. Complete and nearly exclusive extraction of Pb²⁺ was observed in the presence of all cations including Tl⁺. The enrichment ratios of Pb²⁺ in the binary mixtures were approximately 10 while those of the second cation were less than 0.5 except for Sr²⁺ which was 0.86. Corresponding separation factors for Pb²⁺ ranged from 1000 to > 6000.     

Quantum chemical consideration of CO adsorption over cation exchanged faujasite

CNDO/2 calculation for atomic charges, Wiberg bond orders and adsorption energies of CO molecules on the cluster model whose Si/Al ratio varied were carried out. The data for the normal cluster and dealuminated cluster were compared. Decationization energies of the cations increased with the charge densities of cation and number of aluminum involved. Adsorption process of CO on the monovalent cations such as H⁺, Li⁺, Na⁺ and divalent cations, Be²⁺, Ca²⁺, and Mg²⁺ was supposed to be occurring by the donation of non-bonded electrons from CO. The decationization energies of cations obviously decreased by the dealumination process. Adsorption energies of CO on the cations generally decreased as the dealumination look place except the case of H⁺ and Na⁺.     

CO<Subscript>2</Subscript> retention ability on alkali cation exchanged titanium silicate,ETS-10

ETS-10 was ion exchanged by various alkali cations (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) and the BET surface area and pore volume was exactly consistent with cationic size; that is, in the order of Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺. It was observed that a single point adsorption capacity was inversely proportional to cationic size. The largest CO₂ capacity was observed for Li⁺-ETS-10 and it is attributed to greater cation–quadrupole interactions with CO₂ than larger cation. The results also suggests that as the CO₂ loading is increased, the accessibility of adsorbing CO₂ to framework basic O⁻ sites should have become difficult with the increase in cationic size due to the blocking effect by extra-framework CO₂-M⁺. The slight decrease in the slope of adsorption capacity with temperature, especially beyond 373 K for Li⁺-ETS-10 and K⁺-ETS-10 suggests that the adsorption of CO₂ on small alkali cation exchanged-ETS-10 at high temperature is somewhat associated with basic oxygen anion sites in framework due to the existence of large pore. The CO₂-TPD results show that the amount of desorbed CO₂ at higher temperature was proportionally increased due to the increased basicity of oxygen anions in framework. It also shows that the desorption temperature associated with alkali cations in extra-framework (corresponding to low temperature desorption peak) has been lowered with the increase in cationic size, indicating weak cation–quadrupole interactions with CO₂ for larger cations.     

Solid-state nuclear magnetic resonance investigation of cation siting in LiNaLSX zeolites

The location of Li⁺ and Na⁺ cations in a series of dehydrated low-silica LiNaX zeolites (LiNaLSX, framework Si/Al ratio=1.0) were characterized by ⁷Li and ²³Na magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Depending on the Li⁺ content, up to three lines were observed in the ⁷Li MAS NMR spectra attributed to Li⁺ cations on SI′, SII and SIII sites. The ²³Na MAS NMR spectra of the pure sodium form NaLSX and of LiNaLSX samples with low Li⁺ contents contain up to five lines belong to Na⁺ cations located on SI, SI′, SII, and two different SIII′ sites. LiNaLSX zeolites containing more than 40% of Li⁺ show only a single narrow line in the ²³Na MAS NMR spectra attributed to mobile sodium cations. The populations of the different cation sites were determined from the relative line intensities of the MAS NMR spectra. Below about 70% Li⁺ exchange, lithium cations are located only on sites SI′ and SII. Between 70% and 100% Li⁺ content these sites are fully occupied by Li⁺, and the population of site SIII by Li⁺ increases. It was found that the nitrogen-adsorption capacity correlates well with the occupation of Li⁺ at site SIII.     

Cation adsorption at a distearoylphosphatidic acid layer adsorbed at a liquid/liquid interface

The interfacial behaviour of tetraethylammonium cations (TEA⁺) at a liquid-liquid interface modified with an anionic phospholipid layer, distearoyl phosphatidic acid (DSPA), is analysed, with the purpose of characterising the permeation properties of the film. The TEA⁺ concentration in aqueous solution and the amount of DSPA solution employed to generate the lipidic layer, were varied. The results indicate that the layer is tightly compact and the transfer of TEA⁺ cations by permeation does not take place. Instead of this, TEA⁺ ions adsorb at the polar head groups of DSPA, and these adsorbed cations could be acting as nucleation centres of DSPA molecules when the DSPA amount is low.     

Experimental Foam Fractionation Selectivity Coefficients for the Alkali (Group IA) Metals

Abstract

An experimental investigation is presented of the continuous-flow foam fractionation of each of the colligends Li⁺, K⁺, Rb⁺, and Cs⁺ versus Na⁺, the counterion of the dodecylsulfate anion over the aqueous solution concentration range of 1.0 × 10^?4 to 6.0 × 10^?4 M. Initial experiments with K⁺ confirm the achievement of a single-equilibrium-stage separation. Surfactant selectivity coefficients, defined in terms of a colligend-surfactant counterion exchange model at the interfaces of the rising gas bubbles, are established. They represent the ratio of colligend to sodium in the interfacial “stream” to that in the residual steam and are Li⁺, 0.92; K⁺, 1.10; Rb⁺, 1.51; Cs⁺, 1.65. The selectivity sequence is compared to the sequence of absolute partial molal entropies of the cations in aqueous solution.     

Liquid Membrane Separations of Metal Cations Using Macrocyclic Carriers

Abstract

The selectivity in water and methanol solvents of macrocyclic crown ether ligands toward univalent and bivalent cations is well known. Incorporation of these ligands into chloroform liquid membranes separating water and salt solution phases results in a system showing selective cation transport. The cation transport rates of single cations across these liquid membranes have been correlated with equilibrium constant values for cation-macrocycle interaction in methanol. This correlation has been extended to binary cation mixtures of Cs⁺ with Li⁺, Na⁺, K⁺, and Rb⁺. A model for cation transport from these cation mixtures has been reduced to an equation which gives good agreement between measured and predicted transport rates across our liquid membranes.     

Proton-Ionizable Crown Compounds: Transport of Alkali and Alkaline Earth Cations Using Proton-Ionizable Triazolo Macrocycles

Abstract

The macrocycle-mediated flaxes of the alkali and alkaline earth metal cations have been determined in a H₂O-CH₂Cl₂-H₂O bulk liquid membrane system. Water-insoluble proton-ionizable macrocycles of the triazolo type were used. The proton-ionizable feature allows the coupling of cation transport to reverse H⁺ transport. This feature offers promise for the effective separation and/or concentration of alkali metal ions with the metal transport being driven by a pH gradient. A counter anion in the source phase is not co-transported. Transport of the alkali cations only occurred when the source phase pH was greater than the aqueous pK_a value for the carriers. Transport increased regularly with increasing source phase pH. Transport of alkaline earth cations from neutral pH source phases was minimal. The alkali cation selectivity order was K⁺ > Rb⁺ > Cs⁺ > Na⁺ > Li⁺ for the l8-crown-6 sized macrocycles, while little selectivity was observed with the 15-crown-5 sized macro-cycle.     

Extraction of Alkali Metal Cations by Lipophilic Dibenzo-14-crown-4-carboxylic Acids

Abstract

The extraction of alkali metal cations by the lipophilic crown ether, bis-t-octylbenzo-14-crown-4 (BOB14C4), three derivatives of BOB14C4 having pendant carboxylic acid sidearms, and a lipophilic carboxylic acid, 2-methyl-2-heptylnonanoic acid (HMHN) was studied by two-phase potentiometric titration and ion-chromatography. The lipophilic, ionizable crown ethers, BOB14C4-acetic acid (BOB14C4AA), BOB14C4-propanoic acid (BOB14C4PA), and BOB14C4-oxyacetic acid (BOB14C4OAA) extract cations efficiently from aqueous mixed alkali metal chloride solutions into 1-octanol by an ion-exchange mechanism in the range p[H] > 7, as does HMHN. The mode of attachment of the ionizable sidearm, via an ether linkage (BOB14C4OAA) versus a carbon linkage (BOB14C4AA and BOB14C4PA), has a significant effect on the cation selectivity and extraction efficiency of these extractants. BOB14C4 exhibits no p[H] dependent extraction behavior and has no significant effect on the extraction of alkali metal cations by HMHN in a mixture of these two compounds. Although BOB14C4AA and BOB14C4PA extract cations at lower p[H] than HMHN, all three compounds exhibit similar selectivity for Li⁺ over Na⁺, K⁺, Rb⁺ and Cs⁺. A significant reversal in selectivity is observed with BOB14C4OAA, which extracts Na⁺ and K⁺ selectively over Li⁺, Rb⁺, and Cs⁺ and at significanty lower p[H] than BOB14C4AA, BOB14C4PA, or HMHN. The unique behavior of BOB14C4OAA may be attributed to the presence of the ether linkage between the crown ether and the pendant carboxylic acid.     

Strategies for the successful preparation of homoionic smectites

Many chemical, mechanical and thermal properties of smectites depend on the interlayer cations. Therefore, homoionic exchanged smectites are prepared in order to investigate the reaction exchange mechanisms and to improve their behavior as function of the interlayer cation. Presently no general protocol exists and many of the suggested procedures lack proof of achieved exchange. Thus, the aim of the present study was to depict strategies and to determine factors for successful preparation of homoionic smectites. Three natural bentonites and one purified bentonite were saturated by different compensator cations using different (Na⁺, Li⁺, K⁺, Ca^2 +, Mg^2 +, Cu^2 +, or Zn^2 +) chloride solutions. Concentration of the cations in solution varied between 1 and 20 times of CEC. The exchange was repeated one to three times. Extent of smectite interlayer saturation was studied by measurements of cation exchange capacity (CEC) and subsequent determination of the exchanged interlayer cations.Chemical properties of used solution salts influence pH and the surface properties of the smectites. As a result CEC of the smectites was altered by changing contribution from edge charges. It is established that divalent cation exchange was more successful than monovalent cation exchange (Bergaya et al., 2006). Moreover, fractions of high charged 2:1 layers could also hinder homoionic exchange. Finally, successful cation exchange reaction was strongly influenced by soluble accessory minerals and experimental setup.It was found that there is no simple recipe which is equally applicable for all smectites and bentonites, but there is a general protocol considering the following parameters: mineral composition of the sample, smectite CEC and/or layer charge, chemical and mechanical pretreatment, initial interlayer cations, type and concentration of saturating salt, solid–liquid ratio, reaction time, number of repetitions and washing procedure. Finally, proof of interlayer occupation is mandatory.     

Transfer of Monovalent and Divalent Cations in Salt Solutions by Electrodialysis

Abstract

The selectivity mechanism of transport of Na⁺, Ca²⁺ and Mg²⁺ through commercial monovalent‐cation permselective membranes is investigated in batch electrodialysis experiments with synthetic salt solutions containing monovalent and divalent cations. The role of hydration energy, steric effect, kinetic effect as well as effects of permselectivity of cation exchange membrane has been elucidated with electrodialysis of single solutions (NaCl, CaCl₂, MgCl₂). The mechanism of interferences is investigated in (Na⁺/Ca²⁺, Na⁺/Mg²⁺, Ca²⁺/Mg²⁺ and Na⁺/Ca²⁺/Mg²⁺) mixtures.     

Effect of Receiving Phase Anion on Macrocycle-Mediated Cation Transport Rates and Selectivities in Water—Toluene—Water Emulsion Membranes

Abstract

Relative transport rates of metal nitrates (Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, T1⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, and Pb²⁺) were measured alone and in combination with either Pb²⁺, Ag⁺, or T1⁺ in a water-toluene-water emulsion membrane system. The toluene phase contained the surfactant Span 80 and the crown ether dicyclohexano-18-crown-6 (DC18C6). The aqueous receiving phase contained the lithium salt of one of the following anions: pyrophosphate, thiosulfate, hydroxide, chloride, formate, nitrate. In the case of the metal combinations, chloride and formate ions were not studied. Unless significant complexation occurred both between the transported cation and the anion in the receiving phase and between the cation and DC18C6 in the membrane phase, there was little or no transport of the cation from the source phase to the receiving phase. Selective removal of Pb²⁺ and of Ag⁺ from binary mixtures of these cations with each of the cations listed was demonstrated using the emulsion membrane.     

Poly[poly(oxypropylene) phosphate] macroionophores for transport and separation of cations in a hybrid: Cation‐exchange polymer and liquid membrane system

Poly[poly(oxypropylene) phosphate]s (PPOPP, M_n = 5800, 8100, 10,400), with different POP units (400, 1200, 2000), were synthesized and applied as cation‐selective macroionophores in a multimembrane hybrid system (MHS). The solution of PPOPP in dichloroethane formed the flowing liquid membrane (FLM) circulating between two polymer cation‐exchange membranes, and subsequently, between two polymer‐made pervaporation (PV) membranes. It was found that the PPOPP macroionophores activate the preferential transport of Zn²⁺ cations from aqueous solutions containing competing Cu²⁺, Ca²⁺, Mg²⁺, K⁺, and Na⁺ cations. The following separation orders were observed for PPOPPs with POP‐400 and POP‐1200: Zn²⁺ > Cu²⁺ ? Ca²⁺, Mg²⁺, K⁺, Na⁺, and for PPOPP with POP‐2000: Zn²⁺ > Cu²⁺,Ca²⁺ ? Mg²⁺, K⁺, Na⁺. Always, the particular cations are separated as: Zn²⁺ > Cu²⁺, Ca²⁺ > Mg²⁺, and K⁺ > Na⁺. The properties of PPOPPs were compared to respective transport and separation characteristics corresponding to those of respective poly(propylene glycol)s and poly(oxypropylene) bisphosphates. The results of investigation indicate that the bifunctional character of PPOPPs is caused by the presence of ionizable groups and probably pseudocyclic POP structures. By comparing the separation of cations in the simple MHS[FLM] system and the system supported by pervaporation unit [MHS[FLM‐PV] it was found that continuous dehydration of an organic FLM improves the system overall performance. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1436–1445, 2004     

Reversible collapse and Mg release of de- and rehydroxylated homoionic cis-vacant montmorillonites

Homoionic Na⁺, Ca²⁺, Sr²⁺, Li⁺, Cu²⁺ and Zn²⁺ samples of the <2 μm fraction of a cis-vacant montmorillonite from Linden (Bavaria) were steam treated at 200°C (≈1.5 MPa), 240°C (≈3.3 MPa) and 300°C (≈8.0 MPa) after dehydroxylation at temperatures up to 630°C. Cation exchange capacity (CEC) measurements, determination of exchangeable cations and X-ray diffraction (XRD), supplemented by thermoanalytical investigations of the evolved water in a thermobalance linked to a mass spectrometer, infrared (IR) and electron spin resonance (ESR) spectroscopy were employed to obtain information about the state of expandability and structural changes of swellable montmorillonite and the sites of interlayer and octahedral cations after heating and rehydroxylation.The XRD pattern of the initial samples showed a well-defined (001) reflection according to the interlayer cation and its hydration state under laboratory atmosphere. After dehydroxylation the pattern exhibited (001) reflections between 9.6 and 9.8 Å, corresponding to a collapsed structure for all samples. The Na⁺-, Ca²⁺- and Sr²⁺-rich montmorillonites regained partial expandability after rehydroxylation at 200°C and full expandability after rehydroxylation at 300°C if the dehydroxylation temperature was less than 630°C. Rehydroxylation at 300°C of the Cu²⁺- and Zn²⁺-rich montmorillonites did not cause reexpansion, whereas the Li⁺-rich samples recovered a partial swellability after rehydroxylation at 240°C and nearly the full swellability after rehydroxylation at 300°C.The Li⁺-, Cu²⁺- and Zn²⁺-rich samples underwent a strong CEC reduction due to migration of the interlayer cations into the 2:1 layer before dehydroxylation started. After rehydroxylation under water steam Cu²⁺- and Zn²⁺-rich samples released 16–30 meq/100 g of Mg²⁺ from the structure, increasing with the steam temperature. Mg²⁺ release was not observed for the Li⁺-rich montmorillonite.     

Modeling of aqueous electrolyte solutions based on perturbed-chain statistical associating fluid theory incorporated with primitive mean spherical approximation

In this work an equation of state applicable to the system containing electrolytes has been developed by coupling the perturbed chain statistical associating fluid theory (PC-SAFT) with the primitive mean spherical approximation. The resulting electrolyte equation of state is characterized by 4 ion parameters for each of the cation and anion contained in aqueous solutions, and 4 ion specific parameters for each of six cations (Li⁺, Na⁺, K⁺, Rb⁺, Mg²⁺ and Ca²⁺) and six anions (Cl⁻, Br⁻, I⁻, HCO₃⁻, NO₃⁻ and SO₄²⁻) were estimated, based upon the individual ion approach, from the fitting of experimental densities and mean ionic activity coefficients of 26 aqueous single-salt solutions at 298.15 K and 1 bar. The present equation of state with the estimated individual ion parameters has been found to satisfactorily describe not only the densities and mean ionic activity coefficients, but also osmotic coefficients and water activities of single-salt aqueous solutions. Furthermore, the present model was extended to two-salt aqueous solutions, and it has been found that thermodynamic properties such as mentioned above, of two-salt solutions, can be well predicted with the present model, without any additional adjustable parameters.     

Lithium-metal potential in Li<Superscript>+</Superscript> containing ionic liquids

Impedance spectroscopy studies of the interface between lithium and ionic liquid (IL) showed the formation of a film (solid electrolyte interface, SEI), protecting metal from its further dissolution. Consequently, the potential of metallic lithium immersed in an electrolyte containing Li⁺ cations may be described as a Li|SEI|Li⁺ system, rather than simply Li/Li⁺. The potential of lithium-metal in a series of ionic liquids (and in a number of molecular liquids) containing Li⁺ cation (0.1 M) was measured versus the Ag|(Ag⁺ 0.01 M, cryptand 222 0.1 M, in acetonitrile) reference. The lithium-metal potential (E(Li|SEI|Li⁺)) was ca. −2.633 ± 0.017 V in ILs based on the [N(CF₃SO₂)₂ ^– ] anion, while −2.848 ± 0.043 V in ILs containing [BF₄ ^– ] anion (the difference is ca. 200 mV). In the case of ILs based on the triflate anion ([CF₃SO₃ ^– ]), the cation of ionic liquid also influences the E(Li|SEI|Li⁺) value: it was ca. −1.987 ± 0.075 V for imidazolium based cations and much lower (−2.855 V) for the pyrrolidinium based cation. In ionic liquid based on the imidazolium cation and hexafluorophosphate anion ([PF₆ ^– ]), the Li/SEI/Li⁺ potential was −2.245 V. The Li|SEI|Li⁺ potential measured in cyclic carbonates was −2.780 ± 0.069 V while in dimethylsulfoxide showed the lowest value of ca. −3.285 V. The measured potentials were also expressed versus the formal potential of the ferrocene/ferrocinium redox couple, obtained from cyclic voltammetry.     

Modification of layer charge in smectites by microwaves

The layer charge reduction of two Li-saturated montmorillonites is referred to application of microwave radiation at 2.45 GHz for dispersions and 30.0 GHz for the solid powders. Efficiency of these treatments was compared to the same conditions applying conventional heating. The samples were heated in the temperature and time windows corresponding to 190–270 °C and 30–120 min, respectively. Changes in the mean layer charge were monitored by the determination of cation exchange capacity values using exchange of triethylene tetraamino copper ions. The charge reduction of the montmorillonites in aqueous dispersions was rather low (< 30%) despite the fact, that high Li⁺ concentration dissolved in solution was selected (1 mol L^− 1). This behaviour was attributed to the very high water content in used dispersions and high hydration enthalpy of Li⁺ cations. Nevertheless, the microwave heated dispersions (2.45 GHz) showed detectable layer charge reduction as compared to conventionally heated dispersions, where no significant changes were found.Solid powders with different content of exchangeable lithium ions were prepared with solutions having different molar fraction of Li⁺ and Na⁺ cations (0%, 20%, 40%, 60%, 80%, 100% of Li⁺). Final composition of interlayer cations was analysed with ICP-OES. In contrary to dispersions, the microwave treatment of the prepared powders revealed high layer charge reduction, which was much higher than for conventionally heated powders. The efficiency was enhanced with increasing interlayer lithium content but reached a limiting value depending on the montmorillonite used. Migration of the lithium into the structure of the montmorillonite supported with microwaves was extremely fast, finished probably within the few minutes of the treatments. The exchangeable Li⁺ cations are accelerated through alternating electric field of microwaves and highly efficient layer charge neutralisation occurs. Infrared spectroscopy showed that the products obtained with microwave treatments correspond to the materials heated conventionally for much longer periods of time. Hence, applying microwaves the time and energy requirement can be significantly reduced. The X-ray diffraction showed that montmorillonite layers were able to swell in ethyleneglycol upon charge reduction, if the cation exchange capacity was not reduced more than 20–40%.     

Diffusion behavior of univalent cations during cation interchange across an ion-exchange membrane

Measurements have been made of two-cationic cell potentials and cation interchange fluxes for the exchange between K⁺, Na⁺, Li⁺ and H⁺ across a polystyrenesulfonic acid ion-exchange membrane separating solutions of hydrochloric acid and the univalent chloride salts of varied composition. The experimental data have been used to estimate the magnitudes of ionic mobility ratios, membrane ionic concentrations, “effective” single-ion diffusion and interdiffusion coefficients of the interchanging cations in the membrane corresponding to various time intervals during a normal integral cation interchange process. The results indicate that during cation interchange the “effective” single-ion diffusion coefficients of the counterdiffusing cations in the membrane vary markedly over ranges of up to 80% of equilibrium of the interchange processes investigated.