Cation Exchange Selectivity Research Articles

Using Natural Zeolite as a Transporter of Dopamine

Back to table of contents Previous article Next article LettersFull AccessUsing Natural Zeolite as a Transporter of DopamineMona Delavarian, Ph.D. Student, Ali Hassanvand, M.Sc., and Shahriar Gharibzadeh, M.D., Ph.D.Mona DelavarianSearch for more papers by this author, Ph.D. Student, Ali HassanvandSearch for more papers by this author, M.Sc., and Shahriar GharibzadehSearch for more papers by this author, M.D., Ph.D.Published Online:1 Jan 2013https://doi.org/10.1176/appi.neuropsych.12010018AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail To the Editor: Attention deficit-hyperactivity disorder (ADHD) is a developmental disorder that causes problems in attention, monitoring, executive attention, and inhibition responses. Some areas with low activities have been identified in the central nervous system of children with ADHD by SPECT studies.1 One of them, the cortical-striatal-thalamic-cortical network, is known to be the area of dopamine concentration.1 Some evidence showed that the function of dopamine and serotonin are altered in ADHD.2 It is worth noting that anxiety is one of the symptoms that can exist in ADHD as a secondary feature.1Zeolites are crystalline materials that have regular structure. This structure contains TO4 tetrahedra (T=Si and Al) that are linked by O-bridges and form the network of nano-pores. The internal volume of zeolites consists of channels that can have 1 to 3 dimensions, and their pore sizes range from 0.2 nm to 0.8 nm. Zeolites exist both in natural and artificial forms. The natural zeolites are used for many applications and have many properties such as cation concentration and exchange selectivity and can play a role in catalysis, adsorption, and separation systems.3On the other hand, the effects of natural zeolites have been studied on neurons in experimental studies. One research study shows that the clinoptilolite zeolite and montmorillonite are effective to decrease stress and produce a soothing positive effect of sleep.4 Also, the effect of natural clinoptilolite has been studied on the serotonergic receptors in the brains of mice with mammary carcinoma. Zeolite Y is also used for determination and detection of dopamine and serotonin.5We hypothesize that if natural zeolite is used as carrier of dopa into the brain, two advantages may be obtained: 1) increasing dopamine by dopa; and 2) decreasing stress by zeolite. Using this dopa, substituted-zeolite may diminish the side effects of administrating different drugs. Surely, clinical data must be collected to uphold the safety of this hypothesis.Biomedical Engineering Faculty Amirkabir University of Technologye-mail: [email protected]ac.irReferences1 Sadock BJ, Sadock VA: Kaplan & Sadock's Synopsis of Psychiatry: Behavioral Sciences/Clinical Psychiatry, 10th Ed., Baltimore, MD, Lippincott Williams & Wilkins, 2007Google Scholar2 Oades RD: Dopamine–serotonin interactions in attention-deficit hyperactivity disorder (ADHD). Prog Brain Res 2008; 172:543–565Crossref, Medline, Google Scholar3 Auerbach SM, Carrado KA, Dutta PK: Handbook of Zeolite Science and Technology. New York, Marcel Dekker, 2003, pp 17–19Crossref, Google Scholar4 Hecht K, Hecht-Savoley EN: Naturmineralien, Regulation, Gersundheit, 2nd Ed. Strasburg, Germany, Schibri-Verlag, 2007Google Scholar5 Teixeira MFS, Bergamini MF, Marques CMP, et al.: Voltametric determination of L-dopa using an electrode modified with trinuclear ruthenium ammine complex (Ru-red) supported on Y-type zeolite. Talanta 2004; 63:1083–1088Crossref, Medline, Google Scholar FiguresReferencesCited byDetailsCited ByMolecules, Vol. 24, No. 8Biomaterials Science, Vol. 6, No. 5 Volume 25Issue 1 Winter 2013Pages E21-E21 Metrics PDF download History Published online 1 January 2013 Published in print 1 January 2013

Formation of zeolite-like zinc 1,3,5-benzenetriphosphonate open-frameworks by topotactic pillaring of anionic layers

An ab initio powder X-ray crystal structure analysis revealed that layered zinc 1,3,5-benzenetriphosphonates containing interlayer tetramethylammonium (ZBP-TMA) or 4,4'-bipyridinium cations (ZBP-bpy) are transformed to novel isomorphous 3D open-framework compounds ZBP-M (M: K, Rb, and Cs) by treatment in aqueous alkali metal chloride solutions. ZBP-Ms have a pillared layer-type of anionic framework containing 2D zigzag channels connected with cage-like spaces. The potassium atoms in ZBP-K are located near 8MR windows in the 2D zigzag channels, and the potassium cations are successfully exchanged with ammonium cations retaining the open-framework structure. The ammonium form (ZBP-NH4) showed remarkable cation exchange selectivity for Rb(+) and Cs(+) in a mixture of alkali metal cations. It is assumed that zinc ions partially dissolved from the starting layered ZBP precursors are intercalated in ZBP layers to form pillared layered 3D open-frameworks. These results clearly show that topotactic pillared layer approaches are applicable not only to zeolite-related materials but also to novel open-framework metal organophosphonates.

High-resolution electron energy loss spectroscopy of anions chemisorbed on electrode surfaces: The effect of counter cations

In the course of experiments that included Auger electron spectroscopy (AES) and high-resolution electron energy loss spectroscopy (HREELS) on cation exchange at benzoquinone sulfonate chemisorbed on a Pd(111) electrode, it was found that, whereas the AES spectra remained invariant as the counter cation was varied from H+ to K+ to Cs+, profound changes occurred in the HREELS spectra. Specifically, the intensity of the spectral features decreased noticeably when H+ was replaced with K+. And, when the K+ ions were exchanged with Cs+, nothing but a flat-line (dead) spectrum was observed; even the elastic peak was completely attenuated. When the Cs+ ions were displaced by protons, the initial undiminished spectrum was fully restored. This outcome, while unrelated to cation-exchange selectivity, is of exceptional significance in surface electron spectroscopy. It appears that the positive ions on the surface attracted the low-energy incident electrons such that backscattering towards the energy analyzer was hindered; partially by K+ but totally by the larger Cs+ ion. The use of HREELS to examine the molecular integrity of chemisorbed anionic species must thus take cognizance of the possibility that the counter cation chosen to preserve interfacial-layer electroneutrality can have a profound effect. To circumvent such complication, low-valent and small-radii cations will have to be employed. In addition, although subject to instrument limitations, higher incident-electron energies could be adopted. AES, with incident-electron energies in the kV range, is impervious to the presence of counter cations.

Polyethylene/Na+-montmorillonite composites prepared by slurry-fed melt intercalation: Response surface analysis of rheological behavior

Water-assisted melt-intercalation process is a relatively new method for nanocomposite production. Technical challenges notwithstanding, this process is capable of bringing forth good results and promising advantages. Having used this process, we produced composites in a twin-screw extruder. The aim of this study was to find, through a designed set of experiments, the conditions that result in producing nanocomposites. In this study, the main focus of our characterization phase was on rheological behavior. We then used mechanical testing, X-ray diffraction, and atomic force microscopy for verification purposes. The results obtained from these techniques were manifold; therefore, we used response surface method to present them intelligibly. After examining different modifiers, we concluded that chain length, packing density, and cation exchange selectivity are important parameters for choosing proper modifier type. Plus, as has been reported by other groups, this process was found to be mainly diffusion-controlled rather than shear-controlled.

Calcite Growth Rates As a Function of Aqueous Calcium-to-Carbonate Ratio, Saturation Index, and Inhibitor Concentration: Insight into the Mechanism of Reaction and Poisoning by Strontium

Using in situ atomic force microscopy, the growth rates of the obtuse and acute step orientations on the {1014} calcite surface were measured at two saturation indices as a function of the aqueous calcium-to-carbonate ratio and aqueous strontium concentration. The amount of strontium required to inhibit growth was found to correlate with the aqueous calcium concentration, but did not correlate with carbonate, suggesting that strontium inhibits attachment of calcium ions to reactive sites on the calcite surface. Strontium/calcium cation exchange selectivity coefficients, Kex, are estimated at 1.09 ± 0.09 and 1.44 ± 0.19 for reactive sites on the obtuse and acute step orientations, respectively. The implication of this work is that, to avoid poisoning calcite growth, the concentration of calcium should be higher than the quotient of the strontium concentration and Kex, regardless of the saturation index. Previous analytical models of nucleation of kink sites on steps are expanded to include growth rates at...

Na/Ca selectivity coefficients of montmorillonite in perchlorate solution at different temperatures

ABSTRACTThe Finnish spent nuclear fuel disposal is based on the Swedish KBS-3 concept in crystalline bedrock. The concept aims at long-term isolation and containment of spent fuel in copper canisters surrounded by bentonite buffer which mostly consists of montmorillonite. For the long-term modelling of the chemical processes in the buffer, the cation-exchange selectivity coefficients have to be known at different temperatures. In this work, the cation-exchange selectivity coefficients and cation-exchange isotherms were determined in batch experiments for montmorillonite at three different temperatures (25 °C, 50 °C and 75 °C). Five different ratios of NaClO4/Ca(ClO4)2 were used in the experimental solutions. After equilibration the solution and montmorillonite were separated and the solution analysed to get the desired exchange parameters. The experiments were modelled with a computational model capable of taking into account the physicochemical processes that take place in the experiment.

Insights into cation exchange selectivity of a natural clinoptilolite by means of dielectric relaxation spectroscopy

Purified natural clinoptilolite from the Tasajeras deposit, Cuba, and some of its metal exchanged forms are studied, at the dehydrated state, by means of dielectric relaxation spectroscopy (DRS) using two different modus operandi: complex impedance spectroscopy and dielectric dynamic thermal analysis. Data analysis yields the determination of the extra-framework cation (EFC) population into the various possible crystallographic sites of the zeolitic framework as well as of the activation energy characterizing the localized hopping mechanism of EFC. First, it is shown that the DRS responses obtained here match well with the previous reported data, which were previously localized EFCs in positions close to M1 and M2 sites when the clinoptilolite is modified to almost homoionic form. From this outcome, it can be concluded that all EFCs are in the same crystallographic situation regarding solvation or, in other terms, that no steric effect can be taken into account to explain cationic selectivity. Second, based on the assumption that the activation energy for EFC hopping is directly connected to the EFC/framework interaction and on simple thermodynamics consideration, we show this interaction does not govern the EFC exchange reaction. So, it is emphasized that EFC/H2O interaction is the key factor for cation exchange selectivity.

Modelling of cation concentrations in the outflow of NaNO 3 percolation experiments through Boom Clay cores

A laboratory percolation experiment was performed to study the effect of a NaNO 3 plume on the Boom Clay. In this experiment, Boom Clay cores were consecutively percolated with Boom Clay pore water and Boom Clay pore water to which NaNO 3 was added. The concentration of NaNO 3 in the pore water was increased stepwise (0.1, 0.5, and 1 M NaNO 3). The concentrations of Na, K, Ca, Mg and Sr in the eluted water were measured. After every switch of the NaNO 3 concentration, the concentration profiles of K, Ca, Mg, and Sr showed a sharp rise, followed by a slow decrease. It was hypothesised that the cation elution curves are mainly determined by cation exchange processes. Reactive coupled transport modelling with the PHREEQC-2 code was used to describe the experimentally observed elution curves for the cations. Solute transport and water–clay interaction mechanisms, namely cation exchange, were accounted for in the model. Cation exchange parameters (cation exchange capacity and selectivity coefficients) previously determined on non-perturbed Boom Clay ( De Craen et al., 2004) were used. A sensitivity analysis was performed to assess the influence of these parameter values on the goodness of the model to describe the experimental data. The model could fairly well describe the experimentally observed cation concentrations in the eluted water, confirming that cation exchange is indeed the dominant mechanism regulating the cation elution in the percolation experiments.

Novel ultra stable silica-based stationary phases for reversed phase liquid chromatography—Study of a hydrophobically assisted weak acid cation exchange phase

A mixed-mode reversed-phase/weak cation exchange (RP/WCX) phase has been developed by introducing a small amount of carboxylate functionality into a hydrophobic hyper-crosslinked (HC) platform. This silica-based HC platform was designed to form an extensive polystyrene network completely confined to the particle's surface. The fully connected polymer network prevents the loss of bonded phase, which leads to superior hydrolytic stability of the new phase when compared to conventional silica-based phases. Compared to previously introduced HC phases the added carboxylic groups impart a new weak cation exchange selectivity to the base hydrophobic HC platform. The phase thus prepared shows a mixed-mode retention mechanism, allowing for both neutral organic compounds and bases of a wide polarity range to be simultaneously separated on the same phase under the same conditions. In addition, the new phase offers the flexibility that gradients in organic modifier, pH or ionic competitors can be used to affect the separation of a wide range of solutes. Moreover, the inherent weak acid cation exchange groups allow formic and acetic acid buffers to be used as eluents thereby avoiding the mass spectrometric ionization suppression problems concomitant to the use of non-volatile additives such as strong amine modifiers (e.g. triethylamine) or salts (e.g. NaCl) to elute basic solutes from the strong cation exchange phase which was previously developed in this lab. The use of the new phase for achieving strong retention of rather hydrophilic neurotransmitters and drugs of abuse without the need for ion pairing agents is demonstrated.

Cation Exchange Selectivity versus concentration of competing heavy metal cations (Pb2+,Zn2+) : case of Na-montmorillonite

Cation Exchange Selectivity (CES) for Wyoming montmorillonite was determined by equilibration of the clay with a mixed equinormal solution containing two competing cations (i.e. Pb2+, Zn2+). This paper aims at characterizing the structural change and selectivity of a Na-dioctahedral smectite (Wy-Na). The quantitative analysis of XRD patterns is achieved using an indirect method based on the comparison of XRD experimental patterns to calculated ones. Two reference samples were prepared by saturation with Pb2+ or Zn2+ (i.e. two heavy metal cations occurring in hold house trash). The resulting complexes were respectively labelled Wy-Pb and Wy-Zn. After that, the Wy-Na sample was dispersed in solutions containing 0.5Pb2+ and 0.5Zn2+ with different concentrations (from 10−2 N to 10−4 N) in order to understand the concentration effect on the selectivity process of the Na-montmorillonite. The XRD quantitative analysis shows that for low concentrations the d001 spacing value corresponds to Wy-Na complex, whereas for high concentrations the d001 spacing value can be attributed to the Wy-Zn and/or Wy-Pb. At low concentrations, the sample presents a homogeneous state and the cation exchange capacity is saturated with Na+ cation which is characterized by one water layer hydration state (1W). For high concentrations, interstratified hydration behavior appears and the clay has a tendency to exchange in minor contribution the Zn2+ cation and in major contribution Pb2+ cation characterized by a mixed hydration state between one (1W) and two water layers (2W).

Synthesis and characterisation of mesoporous silica phases containing heteroatoms, and their cation exchange properties. Part 3. Measurement of distribution coefficients for uptake of 137-Cs, 89-Sr and 57-Co radioisotopes

Well characterised tunable [1] MCM-41 phases with differing pore structures and containing aluminium, boron and zinc heteroatoms were described in Part 1 [2] to this series. Part 2 [3] illustrated that representative phases exhibited cation exchange selectivity. This part of the series studied the ability of 27 of the phases to take up the environmentally harmful radioisotopes of caesium, cobalt, and strontium, assessed by the measurement of distribution coefficients. Measurements were made in deionised water to simulate ground waters, with 0.1 M HNO 3, 0.1 M NaNO 3, and 0.1 M HNO 3/NaOH solutions, chosen as nuclear waste simulants. In addition the effect of sodium tetraborate and tri-sodium citrate (10 −3 to 10 −6 M) on 57-cobalt uptake was studied. These additives were chosen as relevant to decommissioning/general decontamination (citrate) and Boiling Water or Pressurised Water reactors (borate) encompassing their potential to form complex ions with elements such as cobalt.

Superheated Water Ion-Exchange Chromatography: An Experimental Approach for Interpretation of Separation Selectivity in Ion-Exchange Processes

Cation-exchange selectivity for alkali and alkaline-earth metal ions and tetraalkylammonium ions on a strongly acidic sulfonic acid cation-exchange resin has been investigated in the temperature range of 40-175 degrees C using superheated water chromatography. Dependence of the distribution coefficient (ln KD) on the reciprocal of temperature (1/T) is not linear for most of the ions studied, and the selectivity coefficient for a pair of alkali metal ions or that of alkaline-earth metal ions approaches unity as temperature increases. On the other hand, the retention order of tetraalkylammonium ions is reversed at 160 degrees C or above when eluted with Na2SO4 aqueous solution and the larger ions are eluted faster than the smaller ones contrary to the retention order obtained at ambient temperature. The change in ion-exchange selectivity with temperature observed with superheated water chromatography has been discussed on the basis of the effect of temperature on hydration of the ions and specific adsorption or distribution of ionic species between the external solution and ion-exchange resin. In superheated water, the electrostatic interaction or association of the ions with the fixed ion becomes a predominant mechanism resulting in different separation selectivity from that obtained at ambient temperature.

Selectivity of Co and Ni by K-depleted micas

AbstractContamination of the environment with heavy metals, including cationic radionuclides, is a serious problem which has yet to be fully overcome. A class of potentially effective cation exchangers for sequestering heavy metals which has received little attention is K-depleted mica. The purpose of this study was to investigate the heavy-metal cation exchange properties of K-depleted phlogopite and biotite, which were prepared from a natural phlogopite and biotite, respectively, using sodium tetraphenylborate (NaTPB). The X-ray diffraction (XRD) patterns showed that interlayer K+ ions were completely replaced with exchangeable Na+ ions, resulting in the expansion of the d001 spacing of both K-depleted phlogopite and K-depleted biotite. In order to investigate the cation exchange selectivity of K-depleted phlogopite and biotite for Co2+ and Ni2+, cation exchange isotherms and Kielland plots were constructed. The isotherms and Kielland plots indicated that both K-depleted phlogopite and biotite are highly selective for Co2+ as well as Ni2+. The XRD patterns after both 2Na+ → Co2+ and Ni2+ exchange reactions suggest that double sheets of interlayer water are present in the interlayer. These K-depleted micas are potential cation exchange materials for removal of some heavy metals such as Ni and radioactive species such as 60Co from solution.

On the driving force of cation exchange in clays: Insights from combined microcalorimetry experiments and molecular simulation

We study the origin of the ionic exchange enthalpy in montmorillonite clays using microcalorimetry measurements and molecular simulation. We first determine the standard reaction enthalpy for well-defined interlayer water contents. We then show by a detailed analysis based on thermodynamic cycles that replacing Na + ions by Cs + in the interlayer of montmorillonite clays is an endothermic process, and that the overall exchange is exothermic only because it is dominated by the exothermic replacement of Cs + by Na + in the aqueous phase. This conclusion from ionic exchange enthalpies supports the one of a recent study of the ionic exchange free energy by Teppen and Miller [Teppen B. J. and Miller D. M. (2006) Hydration energy determines isovalent cation exchange selectivity by clay minerals. Soil Sci. Soc. Am. J. 70(1), 31–40] and contradicts long-held views on the role of ion–clay interactions in determining the ionic exchange thermodynamics. This calls for a paradigm shift for the origin of this exchange: The driving force is the “hydrophobicity” of Cs + compared to Na + and not its affinity for clay surfaces.

Cation exchange equilibria of cesium and strontium with K-depleted biotite and muscovite

Cation exchange selectivity for Cs + and Sr 2+ with K-depleted biotite (Na-biotite) and K-depleted muscovite (Na-muscovite) was determined with equilibration for 4 weeks at room temperature. The cation exchange isotherms and Kielland plots indicated that both K-depleted micas show high selectivity for Cs + at low equivalent fraction of Cs + on solid. The K-depleted micas took up Cs up to approximately 50% of their theoretical cation exchange capacities. The XRD patterns after Na + → Cs + exchange reactions with K-depleted biotite showed that the d(001)-spacings collapsed from ~ 12.2 to ~ 11.2 Å with high Cs + concentrations. This collapse suggests that K-depleted biotite is able to immobilize or fix Cs ions in the interlayers. In case of 2Na + → Sr 2+ exchange, K-depleted biotite showed high selectivity for Sr ions at low equivalent fraction of Sr 2+ on solid. The XRD patterns showed that the main d(001)-spacing of the K-depleted biotite slightly increased from 12.16 Å to ~ 12.3 Å after the exchange reactions with the high Sr 2+ concentrations. These results suggest that K-depleted biotite could be used as an ion exchanger to remove radioactive 137Cs as well as 90Sr from groundwater.

Ion-exchange selectivity of a sulfonic cation exchanger based on immobilized cis-tetraphenylcalix[4]resorcinolarene

The ion-exchange equilibrium of protons in SO3H groups of a sulfonic cation exchanger based on immobilized cis-tetraphenylcalix[4]resorcinolarene with cations of Li+, Na+, Ag+, Cu2+, In3+, and protonated 1,3,5,7-tetraazaadamantane in aqueous solutions of electrolytes at 293 K was studied. The corrected coefficients of the cation exchange selectivity were calculated.

Accelerated transport of 90Sr following a release of high ionic strength solution in vadose zone sediments

Numerical simulation of cation exchange and mineral precipitation/dissolution reactions using the multiphase reactive geochemical transport code TOUGHREACT has provided important insight into the distribution of 90Sr among layers of geologic strata in a complex vadose zone at the U. S. Department of Energy's Idaho National Laboratory. During a transfer operation in November 1972, 70.4 m 3 of acidic, high ionic strength liquid containing 15,900 Ci of 90Sr was released over five days into alluvial gravels 137 m above the Snake River Plain Aquifer. Sampling data from perched water zones 33 m below the release contain very high levels of 90Sr as do soil samples obtained nearer the point of release. Use of traditional simulation approaches using laboratory-measured constant partitioning coefficients ( K d) cannot simultaneously explain perched water and soil concentrations. To address the discrepancy, a reactive transport approach was adopted to include competitive cation exchange, dissolution/precipitation of calcite, carbon dioxide gas production and transport, and gibbsite precipitation. Simulation results using this model suggest that some of the 90Sr could have been transported very rapidly immediately after the release with the acceleration facilitated by competition for cation exchange sites with high sodium concentrations in the released liquid and calcium dissolved from calcite, and to a lesser extent by formation of aqueous complexes with nitrate. Once the leading edge of the liquid assemblage was flushed from the alluvium, the mobility of the remaining 90Sr decreased significantly in the absence of the competing cations. Calculations indicate that there should be a net increase in calcite, suggesting that 90Sr could be entrained in the mineral lattice, but insufficient field data exist for confirmation. Sensitivity studies show that the cation exchange selectivity coefficients were the most sensitive individual parameters determining the 90Sr distribution. However, the most sensitive overall quantity was the total ion exchange capacity which is a function of the moles of exchange sites per volume of pore water, the cation exchange capacity, and the total volume wetted by the infiltrating solution. In contrast, the future mobility of 90Sr was found to be relatively insensitive to the normal range in the composition of influxing precipitation and anthropogenic waters.

Reactive transport modeling of column experiments on the evolution of saline–alkaline waste solutions

Leakage of saline–alkaline tank waste solutions often creates a serious environmental contamination problem. To better understand the mechanisms controlling the fate of such waste solutions in the Hanford vadose zone, we simulated reactive transport in columns designed to represent local site conditions. The Pitzer ion interaction module was used, with principal geochemical processes considered in the simulation including quartz dissolution, precipitation of brucite, calcite, and portlandite, multi-component cation exchange, and aqueous complexation reactions. Good matches were observed between the simulated and measured column data at ambient temperature (∼ 21 °C). Relatively good agreement was also obtained at high temperature (∼ 70 °C). The decrease of pH at the plume front is examined through formation of secondary mineral phases and/or quartz dissolution. Substantial formation of secondary mineral phases resulting from multi-component cation exchange suggests that these phases are responsible for a decrease in pH within the plume front. In addition, a sensitivity analysis was conducted with respect to cation exchange capacity, selectivity coefficient, mineral assemblage, temperature, and ionic strength. This study could serve as a useful guide to subsequent experimental work, to thermodynamic models developed for the concentrated solutions at high ionic strength and to other types of waste plume studies.

Synthesis and characterization of silica-based hyper-crosslinked sulfonate-modified reversed stationary phases

A novel type of silica-based sulfonate-modified reversed phase ( −SO 3-HC-C 8) has been synthesized; it is based on a newly developed acid stable “hyper-crosslinked” C 8 derivatized reversed phase, denoted HC-C 8. The −SO 3-HC-C 8 phases containing controlled amounts of sulfonyl groups were made by sulfonating the aromatic hyper-crosslinked network of the HC-C 8 phase at different temperatures. The −SO 3-HC-C 8 phases are only slightly less hydrophobic than the parent HC-C 8 phase. The added sulfonyl groups provide a unique strong cation-exchange selectivity to the hydrophobic hyper-crosslinked substrate as indicated by the very large C coefficient as shown through Snyder's hydrophobic subtraction reversed-phase characterization method. This cation-exchange activity clearly distinguishes the sulfonated phase from all other reversed phases as confirmed by the very high values of Snyder's column comparison function F s. In addition, as was found in previous studies of silica-based and zirconia-based reversed phases, a strong correlation between the cation-exchange interaction and hydrophobic interaction was observed for these sulfonated phases in studies of the retention of cationic solutes. The overall chromatographic selectivity of these −SO 3-HC-C 8 phases is greatly enhanced by its high hydrophobicity through a “hydrophobically assisted” ion-exchange retention process.

Novel clays: Solid-state synthesis, characterization and cation exchange selectivity

Several novel swelling mica-type clays have been synthesized by solid-state processes. Synthetic clays of ideal compositions such as Na 2 Si 6 Al 2 Mg 6 O 20 F 4 · x H 2 O (Na-2-mica), Na 3 Si 5 Al 3 Mg 6 O 20 F 4 · x H 2 O (Na-3-mica) and Na 4 Si 4 Al 4 Mg 6 O 20 F 4 · x H 2 O (Na-4-mica) have been prepared and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and 27 Al and 29 Si solid-state magic angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. Powder XRD showed that all syntheses yielded water swollen micas with c -axis spacing of ∼1.2 nm except in the case of Na-2-mica which also showed a small peak of anhydrous mica phase with a c -axis spacing of 0.96 nm. Solid-state 27 Al MASNMR spectroscopy revealed that almost all the Al is present in the tetrahedral environment of the different micas. Solid-state 29 Si MASNMR spectroscopy revealed different Si (Al) nearest neighbor environments depending upon the composition of the various micas. Selective cation exchange studies were performed on the various micas using 0.5 N NaCl solution containing 12.9 ppm Sr 2+ or 8.12 ppm of La 3+ . The results showed, for the first time, that Na-3-mica has a high selectivity for the trivalent cation tested. The previously reported high selectivity of these synthetic micas for the divalent cations has been confirmed. These selective cation exchange studies are of relevance in cation separations from drinking and waste waters.