Ion exchange and ion transport properties of sulfonated organically modified silica hydrogels

Sulfonated ormosil hydrogels (~80% water) were prepared using tetramethyl orthosilicate as a silica precursor and 2(4-chlorosulfonylphenyl)ethyltrichlorosilane to provide sulfonate functionality for ion-exchange and ion conductivity. Ruthenium(III) hexamine was used as a redox probe in electrochemical studies performed on porous carbon fibre paper electrodes impregnated with the gel. The gel-modified electrodes extracted Ru(NH₃)₆³⁺ from solutions in 0.1 M CF₃CO₂Na_(aq) with a partition coefficient of ~36, and with ~100% of the sulfonate sites being accessible for ion exchange. The Ru(NH₃)₆^3+/2+ couple exhibited reversible and facile electrochemistry in the gel, with a Ru(NH₃)₆²⁺ diffusion coefficient of 4.9×10^–8 cm² s^–1 determined by chronoamperometry. This is an order of magnitude higher than the mobility of this complex in Nafion. The hydrogel-modified electrodes were stable for days, and could be repeatedly loaded with Ru(NH₃)₆³⁺.Special Issue to celebrate the 70^th birthday of Professor Zbigniew Galus     

Highly sensitive sorption-luminescence determination of trace europium with preconcentration on silica chemically modified with iminodiacetic acid

Features of a sorption-luminescence method for the determination of trace europium were studied. The method includes the preliminary sorption of europium at pH 7.1 from solutions with silica chemically modified with iminodiacetic acid, the subsequent treatment of the sorbent with 2-thenoyltrifluoroacetone at pH 8.0, and the measurement of the intensity of luminescence of the surface three-component europium complex at 613 nm. The effect of moisture as the quencher of luminescence of the surface europium complex was studied, and techniques for its removal were proposed. Sorption in the static mode provides the detection limit of europium of 7 × 10⁻⁵ μg/mL. The calibration plot is linear in the range of two orders of magnitude of europium concentration in solutions. The relative standard deviation in the determination of 1.5 × 10⁻² μg/mL europium is 5%. In the dynamic mode of sorption from 1000 mL of an analyzed solution with the use of sorption-desorption, the detection limit of europium of 8 × 10⁻⁷ μg/mL was attained. Original Russian Text ? R.D. Voronina, N.B. Zorov, 2007, published in Zhurnal Analiticheskoi Khimii, 2007, Vol. 62, No. 3, pp. 230–237.     

Highly efficient monolithic silica capillary columns modified with poly(acrylic acid) for hydrophilic interaction chromatography

Monolithic silica capillary columns for hydrophilic interaction liquid chromatography (HILIC) were prepared by on-column polymerization of acrylic acid on monolithic silica in a fused silica capillary modified with anchor groups. The products maintained the high permeability (K=5 x 10(-14)m(2)) and provided a plate height (H) of less than 10 microm at optimum linear velocity (u) and H below 20 microm at u=6mm/s for polar solutes including nucleosides and carbohydrates. The HILIC mode monolithic silica capillary column was able to produce 10000 theoretical plates (N) with column dead time (t(0)) of 20s at a pressure drop of 20 MPa or lower. The total performance was much higher than conventional particle-packed HILIC columns currently available. The gradient separations of peptides by a capillary LC-electrospray mass spectrometry system resulted in very different retention selectivity between reversed-phase mode separations and the HILIC mode separations with a peak capacity of ca. 100 in a 10 min gradient time in either mode. The high performance observed with the monolithic silica capillary column modified with poly(acrylic acid) suggests that the HILIC mode can be an alternative to the reversed-phase mode for a wide range of compounds, especially for those of high polarity in isocratic as well as gradient elution.     

Ion transport mechanism in hybrid MF-4SC membranes modified by silica and posphotungstic heteropoly acid

Transport properties of MF-4SC perfluorinated cation-exchange membrane composites containing hydrous silica and phosphotungstic heteropoly acid (PTA) nanoparticles were studied at various temperatures. Modification of an MF-4SC membrane increases its ion conductivity under reduced humidity by 2.5 orders of magnitude compared to the unmodified membrane and makes the material less humidity-dependent. Comparison of NMR and impedance spectroscopy data implies that water molecules are involved in ion transport in the test samples. Most likely that modification changes the membrane structure at the nanoscale (broadens channels and increases pores) and generates an additional net of hydrogen bonds involving a dopant and sulfo groups of the membrane.     

Reduced-bore monolithic silica column modified with C8-TEOS for reversed-phase electrochromatography

Monolithic silica columns of 2.7 mm ID were prepared and derivatized with C8-TEOS and TEOS by on-column sol-gel reaction. These C8 large diameter monolithic silica columns gave 21 000 theoretical plates for aromatic hydrocarbons in 60% acetonitrile and 40% Tris-HCI buffer. The surface areas as well as the separation reproducibility were improved on coating by the sol-gel approach. Joule heating was greatly reduced by using monolithic columns to which fine quartz sand had been added during column preparation. Since this is a preliminary investigation on a monolithic column with such a large inner diameter, the separation efficiency was not so high as that presently achieved in normal capillary electrochromatography (CEC). However, use of the columns improved sample loadability and concentration detectability of electrochromatography, and semi-preparative separations could be performed.     

Ion exchange studies on natural and modified zeolites and the concept of exchange site accessibility

In the present study natural and Na-rich form of clinoptilolite are examined, in respect to ion exchange of Pb2+, Cu2+, Cr3+, and Fe3+. Equilibrium and kinetic studies performed, under the same normality (0.01 N). Equilibrium studies demonstrate that Na+ enrichment of clinoptilolite is beneficial in respect to metal uptake for all metals, except Cr3+, which is shown to have the same equilibrium behavior in both materials. Kinetic study shows that diffusion coefficients are in the range of 0.16 to 9 x 10(-9) cm2/s, and are not always improved in Na-rich form of clinoptilolite. The effect of temperature on diffusion coefficients is also examined, and Arrhenius activation energy is determined to be in the range of 3.02 to 13.9 kcal/mol, for all metals and materials, except Cu2+, which have extremely low activation energy in the natural sample, equal to 0.04 kcal/mol.     

Zwitterionic ion chromatography with carboxybetaine surfactant-coated particle packed and monolithic type columns

Both particle packed (25 cm x 0.46 cm I.D. SUPELCOSIL 5 microm C18) and monolithic type (10 cm x 0.46 cm I.D. Merck Chromolith Performance C18) reversed-phase substrates were dynamically coated with a carboxybetaine type zwitterionic surfactant ((dodecyldimethyl-amino) acetic acid) and investigated as stationary phases for use in zwitterionic ion chromatography (ZIC). Investigations into eluent concentration and pH were carried out using KCl eluents containing 0.2 mM of the carboxybetaine surfactant to stabilise the column coatings. It was found that eluent concentration decreased anion retention whilst simultaneously increasing peak efficiencies, which may be due to the dissociation of intra- and inter-molecular salts of the carboxybetaine surfactant under higher ionic strength conditions. The Effect of eluent pH was an increase in anion retention with decreased eluent pH due to the increased protonation of the weak acid terminal group of the carboxybetaine, causing both a relative increase in the positive charge of the stationary phase and less repulsion of the anions by the dissociated weak acid group. The carboxybetaine-coated monolithic phase was applied to rapid anion separations using elevated flow rates and flow rate gradients.     

Preparation of chlorocholine chloride/urea deep eutectic solvent-modified silica and an examination of the ion exchange properties of modified silica as a Lewis adduct

Chlorocholine chloride/urea (ClChCl–urea), a deep eutectic solvent (DES), was applied successfully to the modification of silica. The resulting modified silica was characterized by Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller analysis, and elemental analysis. Based on the ClChCl–urea modification of silica, the ClChCl–urea-modified silica is a Lewis adduct with ion exchange properties, and ferulic acid was adsorbed on the ClChCl–urea-modified silica via an ion exchange process. The adsorbed percentage of ferulic acid increased with the increasing amount of modified silica, and a high adsorbed percentage of 89 % could be obtained by the ion exchange process. The Freundlich isotherm used to describe the adsorption of ferulic acid on the modified silica by ion exchange showed a good correlation (R ²?=?0.93). Based on the characterization of the structure and the analysis of the ion exchange property of the ClChCl–urea-modified silica, the modified silica as a potential medium can be applied in some analytical technologies such as solid phase extraction, chromatography, and so on.

Histidine‐modified organic‐silica hybrid monolithic column for mixed‐mode per aqueous and ion‐exchange capillary electrochromatography

A novel organic‐silica hybrid monolith was prepared through the binding of histidine onto the surface of monolithic matrix for mixed‐mode per aqueous and ion‐exchange capillary electrochromatography. The imidazolium and amino groups on the surface of the monolithic stationary phase were used to generate an anodic electro‐osmotic flow as well as to provide electrostatic interaction sites for the charged compounds at low pH. Typical per aqueous chromatographic behavior was observed in water‐rich mobile phases. Various polar and hydrophilic analytes were selected to evaluate the characteristics and chromatographic performance of the obtained monolith. Under per aqueous conditions, the mixed‐mode mechanism of hydrophobic and ion‐exchange interactions was observed and the resultant monolithic column proved to be very versatile for the efficient separations of these polar and hydrophilic compounds (including amides, nucleosides and nucleotide bases, benzoic acid derivatives, and amino acids) in highly aqueous mobile phases. The successful applications suggested that the histidine‐modified organic‐silica hybrid monolithic column could offer a wide range of retention behaviors and flexible selectivities toward polar and hydrophilic compounds.     

应用于全氟辛烷磺酸萃取富集的全氟癸基修饰毛细管硅胶整体柱的制备及应用

利用溶胶-凝胶法,经过烷氧基硅烷的水解、硅羟基的缩聚、凝胶化、陈化、中孔制备、干燥和表面修饰等步骤制备了全氟癸基修饰的毛细管硅胶整体柱。采用该整体柱对全氟辛烷磺酸(PFOS)进行萃取富集,考察其富集特性和效率,并与传统的C18毛细管硅胶整体柱进行对比。结果表明,全氟癸基修饰毛细管硅胶整体柱(15 cm×75 μm)对PFOS具有更高的吸附量和更好的富集选择性,其平均吸附量可以达到75 ng;样品中PFOS的质量浓度为0.25 mg/L时,富集倍数平均可以达到29倍。此全氟癸基修饰毛细管硅胶整体柱对PFOS具有良好的萃取富集性能,可用于水质中痕量PFOS的萃取富集。     

应用于全氟辛烷磺酸萃取富集的全氟癸基修饰毛细管硅胶整体柱的制备及应用

利用溶胶-凝胶法,经过烷氧基硅烷的水解、硅羟基的缩聚、凝胶化、陈化、中孔制备、干燥和表面修饰等步骤制备了全氟癸基修饰的毛细管硅胶整体柱。采用该整体柱对全氟辛烷磺酸(PFOS)进行萃取富集,考察其富集特性和效率,并与传统的C18毛细管硅胶整体柱进行对比。结果表明,全氟癸基修饰毛细管硅胶整体柱(15 cm×75μm)对PFOS具有更高的吸附量和更好的富集选择性,其平均吸附量可以达到75 ng;样品中PFOS的质量浓度为0.25 mg/L时,富集倍数平均可以达到29倍。此全氟癸基修饰毛细管硅胶整体柱对PFOS具有良好的萃取富集性能,可用于水质中痕量PFOS的萃取富集。     

Optimization of instantaneous solvent exchange/surface modification process for ambient synthesis of monolithic silica aerogels

The instantaneous solvent exchange/surface modification (ISE/SM) process for the ambient synthesis of crack-free silica aerogel monoliths with a high production yield was optimized. Monolithic forms of silica wet gels were obtained from aqueous colloidal silica sols prepared via the ion exchange of sodium silicate solutions. Crack-free silica aerogel monoliths were synthesized via an ISE/SM process using isopropyl alcohol/trimethylchlorosilane as a modification agent and n-hexane as a main solvent, followed by ambient drying. The optimum process conditions of the ISE/SM process were investigated by clarifying the reaction mechanism and phenomena. Most effective ranges of process variables on the ISE/SM stage were determined as 0.2500-0.3567 of TMCS/H2O (pore water) in molar ratio and 15-30 of n-hexane/TMCS in volumetric ratio, with a reaction temperature below 283 K. Crack-free silica aerogel monoliths synthesized via these conditions had a well-developed mesoporous structure and excellent properties (bulk density of 0.12-0.14 g/cm3, specific surface area of 724 m2/g), and a high yield (nearly 80%).     

Ion exchange properties of heat-treated NH4Cl-containing cellulose-regenerated

Ion exchange properties of carbon fibers obtained by heat treatment in a temperature range of 200–600°C in an inert atmosphere of cellulose-regenerated impregnated by 0.3–3.0 M ammonium chloride were examined.     

Ion chromatographic determination of hydroxide ion on monolithic reversed-phase silica gel columns coated with nonionic and cationic surfactants

The determination of hydroxide by ion chromatography (IC) is demonstrated using a monolithic octadecylsilyl (ODS)-silica gel column coated first with a nonionic surfactant (polyoxyethylene (POE)) and then with a cationic surfactant (cetyltrimethylammonium bromide (CTAB)). This stationary phase, when used in conjunction with a 10 mmol/l sodium sulfate eluent at pH 8.2, was found to be suitable for the rapid and efficient separation of hydroxide from some other anions, based on a conventional ion-exchange mechanism. The peak directions and detection responses for these ions were in agreement with their known limiting equivalent ionic conductance values. Under these conditions, a linear calibration plot was obtained for hydroxide ion over the range 16 micromol/l to 15 mmol/l, and the detection limit determined at a signal-to-noise ratio of 3 was 6.4 micromol/l. The double-coated stationary phase described above was shown to be superior to a single coating of cetyltrimethylammonium bromide alone, in terms of separation efficiency and stability of the stationary phase. A range of samples comprising solutions of some strong and weak bases was analyzed by the proposed method and the results obtained were in good agreement with those obtained by conventional potentiometric pH measurement.     

Protolytic properties of silica modified with maleinized linseed oil

The protolytic equilibria on the surface of silicas coated with a layer of maleinized linseed oil (MLO), a new type of carboxylic cation exchangers, were studied using potentiometric titration. The ionexchange capacity of the sorbents was determined, a parameter that first increases and then decreases with increasing concentration of MLO on the silica surface. For the dibasic carboxy groups of MLO, pK _a=3.99±0.04 and 4.73±0.04, values close to pK _a for succinic acid, a homogeneous analogue of the system under study.     

Epinephrine‐modified methacrylate monolithic column with fumed silica nanoparticle for pressurized capillary electrochromatography

Via the ring‐opening reaction of epoxy groups with epinephrine, a novel epinephrine functionalized polymethacrylate monolith with fumed silica nanoparticles has been fabricated for pressurized capillary electrochromatography. The preparation of epinephrine‐modified monoliths has been optimized. In addition, morphology, electroosmotic flow, separation mechanism and column performance have been studied. The internal structure of the monolithic stationary phase was more uniform and the column efficiency increased after the incorporation of nanoparticles. With this column, satisfactory separation capability of aromatic compounds and alkaloids has been achieved and the column efficiency for naphthalene reached 138 696 plates/m. As for the real sample, 3 alkaloids were separated in Huanglian Shangqing capsules, a Chinese traditional medicine.     

干凝胶无机整体柱的制备及评价

以硅酸钾为硅源,甲酰胺为催化剂在毛细管内原位聚合形成干凝胶柱,制备了一系列致密度不同的整体柱。该法在柱制备及高温干燥过程中不会发生柱床断裂和塌陷现象,此特点明显优于以烷氧基硅烷为前驱体制备无机整体柱的方法。考察了不同模数硅酸钾对整体柱柱床结构的影响,用扫描电镜(SEM)和氮吸附法对整体柱结构进行了表征,考察了整体柱柱压与流速的关系;对整体柱进行十八烷基修饰后,测定了反相整体柱(C18整体柱)对蒽的柱效,通过考察甲苯在该柱上的突破曲线,获得了其对甲苯的柱容量。结果显示该整体柱柱床刚性好,在高温、高柱压、高流速时柱床能保持其物理结构的稳定性,对蒽的柱效达到41400理论塔板/m,对甲苯的柱容量为61 ng。     

二氧化硅修饰纳米氧化锆陶瓷材料的制备及性能

以二甲基二乙氧基硅烷为硅源,在水溶液中成功制备了SiO2修饰纳米ZrO2颗粒;利用透射电子显微镜、热重分析仪、X射线衍射仪、红外光谱仪分析了样品的形貌和结构;将SiO2/ZrO2与α-Al2O3制成陶瓷材料,考察了其机械性能.结果表明,所制备的SiO2/ZrO2晶粒均一,直径约为10nm,硅原子在SiO2/ZrO2中以Si―O―Zr键合形式存在,SiO2不影响ZrO2的晶型.引入SiO2使得ZrO2晶粒细化、尺寸均匀性提高;SiO2/ZrO2/Al2O3陶瓷气孔率小,具有致密的显微结构和优异的机械性能.     

Chromatographic properties of silica modified with 6,10-ionene and sodium lignosulfonate

Adsorbents for hydrophilic chromatography: silica layer-by-layer modified with 6,10-ionene and sodium lignosulfonate (Sorbent-1), and silica modified with chitosan and sodium lignosulfonate (Sorbent-2) have been investigated. The influence of the nature of polycation used for the synthesis of adsorbents and the composition of the mobile phase on the retention and separation of phenol carboxylic acids have been studied. It was found that the retention of organic acids and the selectivity of their separation are higher on Sorbent-1. The possibility of the isocratic separation of a mixture of caffeine, sorbic, benzoic, vanillic, gallic, salicylic, sinapic, ferulic, p-cumaric, and caffeic acids in 30 min on a column filled with Sorbent-1 was demonstrated.