Acidity Constants of Supported Salts of Heteropoly Acids Using a Methodology Related to the Potentiometric Mass Titration Technique

Using a potentiometric mass titrationmethod, the pK_a values of 12-molybdophosphoric acid (MPA) and 12-tungstophosphoric acid (TPA) were determined in aqueous solution and as a solid suspension in acetonitrile. The results were compared with the earlier reported values obtained using other methods like calorimetry and adsorption (Cal-ad). The acidity values in terms of pK_a and the number of acid sites were determined for the ammonium salts of MPA and TPA, and ammonium salts incorporated with vanadium and ammonium salts impregnated on a ZrO₂ support. The effect of the amount of the salt or acid in the suspension of acetonitrile on the potentiometric titration behavior was also studied and it was found that 0.1 g of the substance gives a good neutralization jump in the titration curve.     

Synthesis,characteristics and adsorption properties of polyphenylene sulfide based strong acid ion exchange fiber

A novel strong acid ion exchange fiber (HO₃S‐BC‐XDC‐PPS) was prepared via crosslinking and grafting copolymerization of 1,4‐bischloromenthyl benzene (XDC), benzyl chloride (BC) on polyphenylene sulfide (PPS) matrix, as well as following sulfonation reaction. The physicochemical structures and properties of the fibrous ion exchanger were characterized with Fourier transform infrared, scanning electron microscopy, thermogravimetric analysis, elementary analysis and chemical titration, respectively. Compared with the preparation of traditional polypropylene–styrene–divinylbenzene‐based ion exchange fibers, the synthesis strategy of PPS‐based strong acid ion exchange fiber avoided the complicated irradiation grafting process with ⁶⁰Co or other radiation facilities. Owing to the existing of thioether (Ar―S―Ar) and sulfoxide (―SO―) unit in fibrous matrix, a super‐equivalent adsorption phenomenon for Cu(II) ion was observed. The HO₃S‐BC‐XDC‐PPS fiber possessed high exchange capacity (≥3.0 mmol/g) and excellent thermostabilities, and the exchange capacity and desorption rate were not decreased after six adsorption desorption cycles. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of LiAlTiO4 and its selectivity to Li+ exchange

The ion-exchanger LiAlTiO₄ of spinel type was prepared by the common precipitation/hydrothermal crystallization method, and was acid-modified. Its ion-exchange properties for alkali ions such as saturation capacity of exchange, distribution coefficient and pH titration curve were determined. LiAlTiO₄ was characterized by the X-ray diffraction method. The acid treatment of LiAlTiO₄ caused Li⁺ extraction ratio to change from 28% to 72%, while the dissolution of Al is less than 6.8%. This inorganic ion-exchanger (LiAlTiO₄-700) has a higher saturation capacity of exchange for Li than for other alkali ions, the saturation capacity of exchange for Li⁺ reaches 4.29 mmol/g (30.03 mg/g); LiAlTiO₄-700(H) has a higher selectivity of ion exchange for Li⁺ than for other alkali ions. These results show LiAlTiO₄-700(H) has better memory and selectivity of ion exchange, and higher capacity of ion exchange for Li⁺. It is a kind of prospective ionic sieve for Li⁺. __________ Translated from Chinese Journal of Applied Chemistry, 2005, 22 (7) (in Chinese)     

Thermal characterization of hydrous tungsten oxides and their behavior as ion exchanger

The preparation, and thermal characterization and ion exchanger behavior of hydrous tungsten oxides obtained from purified tungsten trioxide, by processing of a Brazilian scheelite ore were described. By an alkaline fusion of tungsten trioxide with an excess of sodium carbonate at 900°C an intermediate tungstate product is obtained. Acid lixiviation of the tungstate intermediary in different experimental conditions produces two different hydrous tungsten oxides I and II respectively. A third material was produced by thermal treatment of II, yielding the material IIA, a monohydrate species. The materials prepared were characterized by TG/DTG, X-ray diffractometry and by surface area measurements. Their ion exchange behavior was studied too, using Na⁺ and K⁺ ions as the exchanged species. The inorganic exchanger materials were partially regenerated and may be used consecutively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluation of the acidic properties of hydroxycoumarins and choice of solvents for performing potentiometric analysis

The relative acidity constants (pK_a) for 17 hydroxycoumarins in water, methanol, acetone (Ac), dimethylformide (DMFA), and dimethyl sulfoxide (DMSO) have been determined by Henderson's method. The existence of a linear relationship between pK_a in water and pK_a in acetone, dimethylformamide, and dimethyl sulfoxide has been established. From the pK_a values the sequence of neutralization of the hydroxy groups has been determined: their acidic properties decrease in the sequence 4-OH > 7-OH > 6-OH > 8-OH. A quantitative evaluation of the conditions of titration in five solvents on the basis of the titration constants (pK_t) and of the values of the potential jumps and the shape of the potentiometric titration curves has permitted acetone to be proposed as the optimum solvent for the performance of potentiometric analysis.     

Evaluation of the acidic properties of hydroxycoumarins and choice of solvents for performing potentiometric analysis

The relative acidity constants (pK_a) for 17 hydroxycoumarins in water, methanol, acetone (Ac), dimethylformide (DMFA), and dimethyl sulfoxide (DMSO) have been determined by Henderson's method. The existence of a linear relationship between pK_a in water and pK_a in acetone, dimethylformamide, and dimethyl sulfoxide has been established. From the pK_a values the sequence of neutralization of the hydroxy groups has been determined: their acidic properties decrease in the sequence 4-OH > 7-OH > 6-OH > 8-OH. A quantitative evaluation of the conditions of titration in five solvents on the basis of the titration constants (pK_t) and of the values of the potential jumps and the shape of the potentiometric titration curves has permitted acetone to be proposed as the optimum solvent for the performance of potentiometric analysis.All-Union Scientific-Research Institute of Drug Chemistry and Technology, Khar'kov. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 770–773, November–December, 1985.     

Kinetic and Equilibrium Studies of Chromium(III) Removal by Macroporous Ion Exchanger Amberlyst‐15 (H+)

Chromium(III) sorption on macroporous strong cation exchanger Amberlyst‐15 (H⁺) was studied as a function of time and temperature. The rate constant values for chromium(III) sorption were calculated both for film and particle diffusion processes. The temperature was found to have a positive effect on both the diffusional processes. From the rate constant values, the energy of activation was calculated using the well‐known Arrhenius equation. The high values of energy of activation confirmed the film diffusional nature of the process. Equilibrium data were explained with the help of Langmuir equation. Various thermodynamic parameters (ΔH^?, ΔS^? and ΔG^?) from chromium(III) exchange on the resin were calculated. The ΔG^? values were found to be negative while both the ΔH^? and ΔS^? were positive.     

LiMg0.5Mn1.5O4的合成及对Li+的离子交换选择性

锂及其化合物在航空航天、化工、医药、空调、高能电池和热核反应等方面都有广泛应用，对锂及其化合物的需求与日俱增。我国液体锂资源非常丰富，开发利用其中的锂资源具有重要意义。从盐湖水、地下卤水、盐田母液、油气田水等咸水资源中提取锂的方法有碳酸盐沉淀法、离子交换法、萃取法等。离子     

A multifunctional dual membrane electrodialytic eluent generator for capillary ion chromatography

A multifunctional electrodialytic generator (EDG) for capillary ion chromatography (CIC) is described. The same device can generate acidic, basic or saline eluents. Two oppositely charged ion exchange beads are used to fabricate the EDG; the dual ion exchanger configuration ensures the production of gas-free eluent, obviating the need of a gas removal device used with single ion exchanger EDG's. The ability of the same EDG to produce different eluents is governed solely by the choice of the respective feed solutions; this is presently demonstrated by generation of diverse eluents such as Na₂CO₃/NaHCO₃, CH₃SO₃H, and KNO₃. The EDG is implemented simply in a commercial cross fitting and has been tested up pressures to 2000 psi. Under typical operating conditions, the zero current concentration (open circuit penetration, OCP) is negligible. The generated eluent concentration linearly increases with applied current with a slope that is essentially Faradaic. The device permits both isocratic and gradient operation with good reproducibility, as demonstrated by the analysis of anions using HCO₃⁻/CO₃²⁻ EDG.     

Anthill Earth as a Gold Occurrence Indicator,and Gold Determination by Solid Sampling Flame Atomic Absorption Spectrometry

With the aim of avoiding cumbersome sample treatment, we present a device for the introduction of solid soil samples into AAS-flames for gold determination, as well as the proposition of earth from anthills as a gold occurrence indicator. A previous ground sample of anthill earth (0.50 mg) was weighed directly into a small recipient of polyethylene which was then connected to a sampling boronsilicate glass chamber. The sample was carried by an airflow (5 L min⁻¹) to a quartz cell positioned between the burner top and the optical beam. The generated atomic vapor produced a transient signal which was totally integrated in three seconds. The performance was compared with conventional flame atomic absorption spectrometry after proper sample digestion. No significant differences were observed between both procedures (mean deviation ±1.90%), and a LOQ of 0.03 μg Au was achieved using the proposed method. The anthill earth was found to be very suitable for indication of gold occurrence in soils and related materials.     

A new inorgano-organic ion exchanger; p-chlorophenol anchored to zirconium tungstate

Summary A new inorgano-organic ion exchanger, ZWpCP, prepared by anchoring p-chlorophenol to zirconium tungstate (ZW), exhibits good ion exchange capacity. Both ZW and ZWpCP were characterized by elemental analysis, thermal studies (t.g.a.) and spectral analysis (i.r. and FT-i.r.). The chemical stability of the products has been checked in acidic, basic and neutral organic media. The comparative ion exchange capacity and distribution behaviour of ZWpCP towards metal ions has been studied.     

Crown-Containing N-(Thio)Phosphoryl-(Thio)Ureas,their Ligand Properties and Analytical Application

Abstract

Crown-containing N-(thio)phosphoryl(thio)ureas are related to a class of NH-acids due to the presence of two acceptor-groups: (thio)phosphorylic and (thio)acylic. In agreement with structure of lariat ether, it was observed a stage corresponding to the step ejection of two H* ion on the potentiometric titration curve of ligand by alkaline. Calculated step ionization constants demonstrate that these compounds are weak acids with relative values of pK₁ and pK₂.     

Chromatographic properties of zirconia-based stationary phases for ion exchange chromatography having surface bound cationic functions

A series of non-porous, microspherical zirconia-based stationary phases with surface bound cationic functions have been introduced and evaluated in ion exchange chromatography of proteins and small acidic solutes. Different surface modification procedures were evaluated in the covalent attachment of weak, strong or hybrid anion exchange moieties on the surface of non-porous zirconia micropar-ticles. N,N-Diethylaminoethanol (DEAE) was used as the weak anion exchange ligand while glycidyltrimethylammonium chloride, which was covalently attached to poly(vinyl alcohol) layer (PVAN) on the zirconia surface, constituted the strong anion exchange moiety. Partially quaternarized poly(ethyleneimine) hydroxyethylated (PEI) was used as the hybrid type of anion exchange coating. DEAE-zir-conia microparticles acted as purely cation exchange stationary phases toward basic proteins indicating the predominance of electron donor-electron acceptor interaction (EDA) with surface exposed zirconium sites as well as cation exchange mechanism via electrostatic interaction with unreacted and unshielded hydroxyl groups. PVAN-zirconia stationary phase exhibited anion exchange chromatographic properties toward acidic proteins, but EDA interaction has stayed as an important contributor to solute retention despite the presence of a relatively thick layer of poly(vinyl alcohol) on the surface of the zirconia particles. The modification of zirconia surface with partially quaternarized PEI proved to be the most effective approach to minimize Lewis acidic metallic properties of the support. In fact, PEI-zirconia stationary phase operated as an anion exchanger toward acidic proteins and other small acidic solutes.     

Determination of dissociation constants of species oxidizable in aqueous solution by air oxygen on an example of quercetin

The comparison of literature data on the dissociation constant of one of the most abundant natural flavonoids, e.g., quercetin, demonstrates their irreproducibility. The reason for this likely corresponds to the easiness of its oxidation by air oxygen during the titration process. To eliminate such problems, a modified version of potentiometric titration was proposed with bubbling a weak flow of an inert gas (nitrogen) through the solution to be titrated in the presence of minimal amounts of a nonionic surfactant. By virtue of the technique proposed, the values of pK _a for quercetin were measured to be 6.62 ± 0.04 and 9.7 ± 0.3. The first one corresponds to the hydroxyl group in the γ-pyrone fragment of the molecule, while another agrees with the typical values of pK _a for phenols.     

Thermal and Potentiometric Titrations of Phytic Acid

Abstract

Values for the ionization constants and the heats of ionization of phytic acid (inositol hexaphosphate) have been determined by simultaneous potentiometric and thermal titration in a titration microcalorimeter. The potentiometric results are in substantial agreement with those found by discontinuous titration; the heat liberated from pH 10.4 to 6.8 is essentially that found using a batch microcalorimeter. Ionization of phytic acid may be generally characterized as having five groups similar to pK of phosphoric acid, two groups similar to pK2 of phosphoric acid and 4 groups similar to pK4 of pyrophosphoric acid. A single group has pK ～ 5 with ΔH_i ～ -1.1 kcal/mol.     

Preparation and characterization of nano-ZnO flakes prepared by reactive ion exchange method

Nano-ZnO flakes were synthesized by calcination of the precursor of Zn(OH)₂ obtained via the reactive ion exchange method between an ion exchange resin and ZnSO₄ solution at room temperature. Scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscope, UV-Vis diffuse reflection spectrum and Na₂EDTA titration were used to characterize the structure features and chemical compositions of the as-prepared ZnO. The results show that the as-prepared ZnO flakes have uniform structure and high purity. Heat capacities in the temperature range of 83 to 396 K were measured. The measured heat capacities values were compared with those of coarse crystal powders and the difference between this two heat capacity curves was analyzed.     

Investigation of Acid-Base Equilibria for Symmetrically Substituted <Emphasis Type="Italic">P,P</Emphasis>′-Dialkyl Partial Esters of Bisphosphonic Acids

Bisphosphonic acids are powerful metal chelating reagents with a wide spectrum of applications. A series of partial ester derivatives of bisphosphonic acids was synthesized in order to investigate the physico-chemical changes induced by partial protection of the acid groups. The acid dissociation constants K₁ and K₂ for a homologous series of short-chain aqueous-soluble dibasic bisphosphonic acids, i.e., the P,P′-diethyl methylene-, ethylene- and propylene-bisphosphonic acid partial esters, H₂DEt[MBP], H₂DEt[EBP] and H₂DEt[PrBP], respectively, were determined by potentiometric titration and ³¹P NMR spectrometry. All three diethyl esters are rather acidic with pK₁ < 1.2 and pK₂ < 2.2. The influence of the separation between the phosphonate groups on ligand acidity and successive pK_a values is rationalized in terms of solvation, inductive and electrostatic effects.     

离子交换色谱中混合保留机理的研究

鉴于离子交换色谱中被测离子和有机聚合物树脂之间存在的吸附作用, 选择阴离子交换色谱柱IonPacAS9-HC为研究对象, 针对离子交换色谱中的吸附保留行为, 从色谱混合保留机理的角度出发, 考虑各色谱柱固定相含量和界面吸附面积的不同, 建立柱间保留的相互关系方程. 在五根不同批号IonPacAS9-HC (250 mm×2 mm I.D.)柱上, 以含50%乙腈(V/V)的9 mmol/L Na₂CO₃为流动相, 0.25 mL/min流速, 对12个不同结构类型的无机和有机阴离子(氟离子、氯离子、硫酸根、磷酸根、二羟基丁酸、丙酮酸、乙酸、丙烯酸、苯甲酸、丙二酸、酒石酸和邻苯二甲酸)的保留行为进行研究, 并采用推导所得的混合保留机理模型对溶质这一保留特征进行表征, 结果较为理想, 其中一价离子的相关系数为0.9～0.999, 二价离子的相关系数为0.999～1, 为离子交换色谱中吸附保留行为的研究提供了新方法.