Selective separations by reactive ion exchange : Part III. Preconcentration and separation of oxo anions

A new procedure for simultaneous preconcentration, separation, and determination of permanganate, chromate and vanadate was developed for aqueous solutions containing p.p.b. levels of these anions (and molybdate). The presence of other (non-complexing) ions in p.p.m. concentrations did not interfere. The procedure consisted of reactive adsorption of all three anions as their reduced cations, on iron(II)-treated resin, followed by elution of vanadium(IV) with 0.01 M HNO₃/H₂O₂, manganese(II) with 0.35 M HCl, and chromium(III) with 4M HCl. Concentration factors of 40 were obtained with 1-l “samples” 10 p.p.b. concentrations were determined with standard deviations of 4–5 % by a.a.s. and conventional spectrophotometry.     

Spectrophotometric determination of vanadium(IV) with nitrilotriacetic acid

A new and convenient spectrophotometric method for the estimation of vanadium(IV) with NTA is described. The minimum ratio of metal ion to ligand, working pH, wavelength for maximum absorbance of the complex ion, and the effect of various cations and anions are described. The complex ion obeys Beer's law in the concentration range 1–32 mmol/liter of the vanadium(IV) ion. It is observed that iron(II), cobalt(II), nickel(II), copper(II), and oxidizing anions such as chromate and nitrite interfere in this determination, whereas managanese(II), chromium(III), iron(III), and anions like nitrate, chloride, bromide, iodide, thiocyanate, sulfate, and sulfite do not have any effect. Excessive amounts of acetate, phosphate, oxalate, tartrate and thiosulfate must also be avoided in this determination. Anions and cations which interfere in the determination of vanadium(IV) by NTA should not be present in the system.     

Equations for the Partition of Neutral Molecules, Ions and Ionic Species from Water to Water–Ethanol Mixtures

Equations set up for the transfer of neutral solutes from water to water?Cethanol mixtures can also be used to correlate the transfer of ions and ionic species, as log₁₀ P, where P is the partition coefficient. Only two additional terms are required in the equations, one for anions and one for cations. The extended equations can fit log₁₀ P values for anions and cations with a standard deviation of about 0.2 to 0.3 log units for transfer of 41 anions and cations from water to various water?Cethanol mixtures from 10?% ethanol to 100?% ethanol by volume. The log₁₀ P values for carboxylate anions and protonated amine cations as obtained from the variation of pK _a with solvent are quite compatible with log₁₀ P values for simple anions and cations.     

Simultaneous ion-pair chromatography of inorganic anions and cations using on-column derivatization with chelating agents and UV detection

Six complexones have been investigated as on-column derivatizing agents for the simultaneous separation of inorganic anions and cations using ion pair chromatography. UV spectrophotometry at 210 nm has been applied for both the direct and the indirect detection of anions and anionic metal complexes. Under the experimental conditions used DCTA and DTPA have been practically applicable. Factors affecting the chromatographic behaviour of analyte ions have been studied. Chloride, nitrite, nitrate sulphate, chromate, molybdate, iron, chromium (III), copper (II), cobalt (II), nickel (II) and mercury (II) ions have been separated in 30 min with a mobile phase containing 1 mmol/1 TBA and 0.5 mmol/1 DCTA at pH 6.2 in acetonitrile-water (10:90 v/v). With DTPA as eluent and using pre-column derivatization of metal cations with DCTA eight anions and six metal cations can be separated. The detection limits are less than 0.1 mg/l for most of the investigated ions. Permanent address: Department of Analytical Chemistry, Vilnius University, Naugarduko 24, 2006 Vilnius, Lithuania     

Analytical derivation of the Hückel “4n + 2 rule”

The “4n + 2 rule” is derived analytically at the level of the simple Hückel theory for neutral even-membered chains, their double ions, as well as cations and anions of the odd-membered chains, by determining the first order energetic effect of the ring closure. The topological background of the “4n + 2 rule” is also briefly discussed.     

Fast spectrophotometric determination of titanium in rocks with 3,4-dihydroxybenzoic acid

A fast Spectrophotometric method has been developed for titanium determination in geological matrices, based on the mixture of the sample solution with an exact volume of a single chromogenic solution containing acetate buffer, ascorbic acid and 3,4-dihydroxybenzoic acid DHB, which forms with titanium(IV) ions a yellow complex with absorption maximum at 380 nm. The following parameters were studied: complex stability, pH effect, amount of DHB, amount of acetate buffer, obedience to Beer's law, amount of ascorbic acid and iron masking. The results demonstrated that titanium can be determined in the pH range 4.0–5.0, with a molar absorptivity of 1.43 × 10⁴ 1·mol^–1 cm^–1 and a limit of detection of 2.3 ng/ml. The methodology that allows analysis of 30 samples per hour. Common anions and cations do not interfere, even when present in large amounts. Iron(III) interference can be easily eliminated by reduction to iron(II) using ascorbic acid. Analytical characteristics of the proposed procedure, such as calibration sensitivity, analytical sensitivity, limit of detection and coefficient of variation, were determined. The procedure was applied for titanium determination in various standard geological matrices, with results of satisfactory accuracy and precision (RSD<1%).     

A new approach for the study of gas-phase ion-ion reactions using electrospray ionization

A simple flow reactor which facilitates the study and application of ion-ion and ion-molecule reactions at near atmospheric pressures is reported. Reactant ions were generated by electrospray ionization and discharge ionization methods, although any ionization sources amenable to atmospheric pressure may be used. Ions of opposite charge are generated in spatially separate ion sources and are swept into capillary inlets where the flows are merged and where reaction(s) can occur. Among the reactions investigated were the partial neutralization of multiply protonated polypeptides and proteins such as melittin, bradykinin, cytochrome c, and myoglobin by reaction with discharge-generated anions, the partial neutralization of multiply charged anions of oligodeoxyadenylic acid (d(pA)₃) by reaction with discharge-generated cations, the partial neutralization of bovine A-chain insulin anions by reaction with myoglobin [M+nH]ⁿ⁺ ions, and the reaction of multiply protonated melittin with discharge-generated cations. The cation-anion reactions generally resulted in a shift to lower charge (higher mass-to-charge ratio) in the products’ charge state distributions and the transfer of solvent molecules to the macromolecule products. Multiply protonated melittin was detected in a less highly solvated state with the positive discharge in operation.     

Effect of Alkali Metal Cations on the EDL Structure at a Gold Electrode in Alkali Solutions

Effect of the nature of cations of alkali metals on the EDL structure during adsorption of hydroxide ions at a gold electrode is considered. It is shown that the reason for such an effect can be the pulling of cations into the dense layer resulting from the formation of associates of cations and specifically adsorbed anions OH^–. Parameters that reflect this phenomenon are estimated quantitatively.     

Ternary and tetrahedral symmetry in hybrid fluorides, fluoride carbonates and carbonates

Tren amine cations and carbonate anions adopt a ternary symmetry while tetra amine cations are tetrahedral. The symmetry of these constitutive ions influences strongly the nature of the solids which crystallise from solutions. Large fluorinated aluminate polyanions with tetrahedral symmetry appear in the presence of tren amine, while infinite chains of AlF₆ octahedra are observed with tetra amine and that noncentrosymmetric structures are frequently encountered in rare earth fluoride carbonates.     

Effects of Metal Ion Adduction on the Gas-Phase Conformations of Protein Ions

Changes in protein ion conformation as a result of nonspecific adduction of metal ions to the protein during electrospray ionization (ESI) from aqueous solutions were investigated using traveling wave ion mobility spectrometry (TWIMS). For all proteins examined, protein cations (and in most cases anions) with nonspecific metal ion adducts are more compact than the fully protonated (or deprotonated) ions with the same charge state. Compaction of protein cations upon nonspecific metal ion binding is most significant for intermediate charge state ions, and there is a greater reduction in collisional cross section with increasing number of metal ion adducts and increasing ion valency, consistent with an electrostatic interaction between the ions and the protein. Protein cations with the greatest number of adducted metal ions are no more compact than the lowest protonated ions formed from aqueous solutions. These results show that smaller collisional cross sections for metal-attached protein ions are not a good indicator of a specific metal–protein interaction in solution because nonspecific metal ion adduction also results in smaller gaseous protein cation cross sections. In contrast, the collisional cross section of α-lactalbumin, which specifically binds one Ca²⁺, is larger for the holo-form compared with the apo-form, in agreement with solution-phase measurements. Because compaction of protein cations occurs when metal ion adduction is nonspecific, elongation of a protein cation may be a more reliable indicator that a specific metal ion–protein interaction occurs in solution.      

X-ray photoelectron spectroscopy investigation of perovskites La1−x Sr x FeO3−y (0 ≤x < 1.0), prepared via a mechanochemical route

Perovskite-structure oxides La_1?x Sr _x FeO_3?y (x = 0, 0.2, 0.6, 1) were synthesized by the mechanochemical method. In order to refine the stoichiometric composition and the charge state of ions, these samples were studied by X-ray photoelectron spectroscopy (XPS). An investigation of perovskites with x = 0, 0.2, and 0.6 in air at room temperature showed that these samples do not contain oxygen vacancies (y = 0), i.e., they are fully oxidized. Hence, to produce electrical neutrality, these samples should contain iron(4+) cations in an amount proportional to the degree of substitution (x) of strontium(2+) for lanthanum(3+). However, no Fe⁴⁺ cations were found in the oxides. All perovskites contain only Fe³⁺ cations, oxygen ions O^2? along with oxygen ions with reduced electron density (O^?). These data provid evidence of the possible electron density redistribution from oxygen ions to iron cations. The fact that the oxides contain oxygen ions with reduced electron density suggests that weakly bound lattice oxygen in substituted perovskites is represented by O^? ions.     

Solochrome Violett R. S. as a new colorimetric reagent

Summary The reaction between molybdenum and the sulphonic acid azo dye Solochrome Violet R.S. has proved to be a suitable one for the microdetermination of Mo amounts covering the range of 0.3 to 10 ppm in purely aqueous solutions. The variation of extinction with concentration conforms satisfactorily with Beer's law throughout the whole range. Very many cations and anions do not interfere with such a determination. Ferric iron up to 2 mg per 25 ml is completely masked with ascorbic acid.Part II: Khalifa, H., and S. W. Bishara: Z. analyt. Chem. 178, 345 (1960).     

Paper chromatography in the separation of ions

A study has been made of the separation of ions of the alkali metals, alkaline earth metals, elements of groups IIIA and B and of anions, such as arscnate, phosphate, vanadate, molybdate, tungstate and chromate, with solvent mixtures of tert.-butyl alcohol, water and hydrochloric or acetic acid in the ratio of 7:2 1, and with 01 without tartaric, citric or malonic acid. The solvent mixture with hydrochloric acid as one of the components was found to be most effective for the separation of six cations or three anions from their mixtures. The rl and R1 values and the sequences of separations have been recorded     

Infrared spectra of bis(trifluoromethanesulfonyl)imide based ionic liquids: Experiments and DFT simulations

We measured the far- and mid-infrared spectra of three ionic liquids having bis(trifluoromethanesulfonyl)imide anions and three different cations of the families of pyrrolidinium and ammmonium ions. The molecular vibrations of the individual ions were calculated by means of DFT theory at the B3LYP/6-31G** level: we found good agreement between the experimental and the computed frequencies. The infrared lines are ascribable to molecular vibrations of the single ions, suggesting an extremely weak interaction between anions and cations. The spectral lines found experimentally between 760 and 1050 cm⁻¹ are fingerprints for different cations. The comparison with the calculated frequencies allows the assignment of the experimental spectral lines to specific molecular vibrations of anions and for the first time of the specific cations of the measured ionic liquids.     

Determination of glycine,alanine, and leucine at different solution ph with the aid of donnan potential sensors based on hybrid membranes

The cross sensitive sensors whose analytical signal is the Donnan potential (PD-sensors) were developed for the determination of the amino acids glycine, alanine, and leucine in acidic and alkaline solutions. Hybrid materials based on perfluorinated sulfo cation-exchange membranes Nafion and MF-4SC with incorporated zirconium dioxide and silicon dioxide nanoparticles, including those with modified surfaces containing proton-acceptor groups, were used in the PD-sensors. The sensitivity of the PD-sensors to hydronium ions, which interfere with the determination of amino acids at pH < 7, was considerably decreased due to the use of the membranes obtained by an in situ method that contained silicon dioxide nanoparticles with amine-containing groups. The greatest sensitivity of the PD-sensors to the anions of amino acids at pH > 7 and the smallest sensitivity to the cations K⁺ were observed in hybrid membranes, which combined an increased rate of anion transfer and a low moisture capacity. The use of the PD-sensors based on hybrid membranes makes it possible to determine the cations, anions, and zwitterions of amino acids over a wide range of pH with a sufficiently high accuracy.     

Liquid-liquid extraction of iron(III) and gallium(III) with macrocyclic Schiff bases containing bisphenol A subunits

The quantitative extraction of iron(III) and gallium(III) was investigated with the recently synthesized macrocyclic Schiff base containing bisphenol A subunits. The phenol groups in the Schiff base moiety led to a large increase in the percent extraction of trivalent metal ions. The substitution of methoxy groups for phenolic OH ligands resulted in a marked decrease in the extractability of metal ions, and no iron(III) was extracted. The corresponding acyclic Schiff base was found to have a reasonable reactivity toward metal ions and a better solubility in organic solvents. The iron(III) and gallium(III) complexes with macrocyclic and acyclic Schiff bases were quantitatively extracted into nitrobenzene without the presence of bulky counter anions. A single extraction gave a good separation of iron(III) from iron(II) in the mole ratios 4:1 to 1:3. The red iron(III) complexes can be used for the extraction-spectrophotometric determination of iron(III). The apparent molar absorptivity at 518 nm is 5.43 × 10³lmol⁻¹ cm⁻¹.     

盐对甲醇微观结构的影响

利用拉曼光谱研究盐对甲醇微观结构的影响.比较了不同盐/甲醇体系的O—H伸缩谱段和C—O伸缩谱段的超额拉曼光谱,对比给出了阴、阳离子与甲醇的相互作用.O—H伸缩谱段的超额拉曼光谱明显地显示了阴离子与甲醇形成弱氢键,氢键强度排序为CH3OH-CH3OHCl--CH3OHNO3--CH3OHClO4--CH3OH,在这个波段内,基本观察不到阳离子与甲醇的相互作用.在C—O伸缩谱段内,阴阳离子均有显著的体现,且与它们作用的甲醇C—O伸缩振动频率有如下的关系:CH3—OH(阴离子)CH3—OH(体相)CH3—OH(阳离子).根据C—O伸缩谱段的超额拉曼光谱,拟合了该谱段的拉曼光谱,由分解的谱峰强度得到阴、阳离子第一溶剂化层中甲醇分子的数目,结果显示在该浓度(～0.005)下离子对第一溶剂化层以外的甲醇氢键网络结构没有明显影响.     

团簇尺寸对奇数和偶数磷团簇离子信号强度差异的影响

磷原子形成的奇数和偶数团簇离子的信号存在明显的强度差异. 当团簇离子尺寸n>25时, 奇数团簇离子的信号强度一般会远远超过其邻近的偶数团簇离子. 为更好地理解团簇尺寸对这一现象的影响, 本文通过真空中激光溅射红磷的方法, 利用质谱对磷团簇离子进行了研究和分析. 结果表明这种方法可以产生较大尺寸(n~500)的磷团簇离子. 进一步对团簇离子的强度分布进行分析表明: 随着正负离子团簇尺寸的增加, 奇/偶数离子强度差异都会逐渐减小. 根据它们的变化趋势, 可以预测: 当n>1000时, 奇/偶数离子强度交替的现象可能会消失. 这一结果正反映出团簇在从原子演变到凝聚态物质过程中的桥梁作用.     

Simultaneous detection of monovalent anions and cations using all solid-state contact PVC membrane anion and cation-selective electrodes as detectors in single column ion chromatography

The overall efficiency of ion chromatographic procedures allows the possibility of routine separation and detection of common inorganic and organic anions and cations at low levels in a simultaneous system. A simple and rapid independent separation, and sensitive simultaneous detection of monovalent common anions and cations were achieved using 2 mM copper sulfate, (at pH: 5.40), as eluent with low cell-volume potentiometric detectors. This was established using all-solid state contact, tubular, PVC-matrix membrane anion and cation-selective electrodes in series as detectors with mixed-bed ion-exchange column in ion chromatography. The developed method is reproducible and highly selective to monovalent anions and cations, and takes less than 8 min. Under all operation conditions, the detection limits of the developed method, for potassium, rubidium, cesium, thallium(I), nitrite, nitrate, benzoate and bromide, were of the order of tens of ppb, for sodium, ammonium, chloroacetate, cyanate and chloride ions, values were of the order of hundreds of ppb for an injected volume of 20 mul. The method was flexible since most of anions do not interfere the detection of cations and most of cations do not affect the detection of anions, so that the method can be applied to many sample types e.g. environmental. The application of the method for river, sea and tap water samples were illustrated.     

Hydration numbers of sea water basic ions found by the pulse method of proton NMR

Hydration numbers of basic ions in sea water (SW) are found from a proton relaxation rate of 1/T ₁ in SW and model solutions. A possibility for the formation of three-layer hydrate shells around main SW cations and two-layer shells around anions is ascertained. About half of water molecules is in influence zones of ions in sea water that correlates with a double shift in the baric dependence maximum of T ₁ to a smaller pressure in SW relative to pure water.