Influence of the way of preparing vanadium phosphorus oxide (VPO) precursor and introducing multi-additives on the reaction performance

Spatial patterns of the uncatalyzed bromate – catechol – sulfuric acid system in a thin fluid layer were observed. A mixture of dots, strips and circles was formed by interaction of chemical reaction, diffusion and hydrodynamic instabilities.     

Morphology Evolution During Polymer Crystallization Simultaneous Calorimetric and Optical Measurements

The crystallization of the isotactic poly(propylene) (I-PP) has been studied carrying out measurements by means of a special calorimeter connected to a microscope and a digital acquisition system of images. To authors' knowledge, this is the first time that simultaneous calorimetric and optical measurements are carried out on polymers. The analysis of Polarized Optical Microscopy images has allowed the appraisal of nucleation density and growth rate in isothermal and non isothermal conditions. The results obtained in isothermal conditions have been analyzed through the Kolmogoroff model and the crystallinity calculated from the model has been compared with that obtained from the calorimetric measurements.     

Titration Calorimetric Investigations on the Interactions of Zn(II) Porphyrin Complexes with Pyridine in Benzene and Chloroform at 298.15 K

Titration calorimetry was used in a thermodynamic study on the interactions of pyridine with natural zinc(II) porphyrin derivatives in benzene and chloroform at 298.15 K. The ability of zinc porphyrins to coordinate to pyridine is higher in benzene than in chloroform and also depends on the molecular structure of the metalloporphyrin.This revised version was published online in November 2005 with corrections to the Cover Date.     

Potentiometric Studies of Some Bivalent Metal Ion Complexes of a New Ligand,o-(2-Thiazolylazo)-4-Ethylphenol

Abstract

The complexations of a new ligand, o-(2-thiazolylazo)-4-ethylphenol(TAEP) with Ca(II), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hq(II) and Pb(II) have been studied by potentiometric titrations, at 25.0 ± 0.2°C and an ionic strength of 0.1 in 30% v/v dioxane-water mixture. The dissociation constant and spectral data of TAEP and formation constants of the complexes containing various molar ratios of metal ion to ligand, are reported. It is observed that Ca(II) forms only an ML complex in any molar ratios, whereas other metal ions react in two steps forming ML and ML₂ complexes in a 1:3 molar ratio. In the case of 1:1 and 1:2 molar ratios, Mn(II), Co(II), Cd(II) and Hg(II) seemed to form bi- or poly-nuclear complexes because of slightly different formation curves from those of 1:3 molar ratio. The sequence of the first successive formation constant is Cu > Hg > Ni > Pb > Co > Zn > Cd > Mn > Ca, showing Mellor-Maley's order. Further correlation is shown between the formation constants and the second ionization potentials of the metals.     

Novel Copper(II)-Selective Potentiometric Sensor Based on a Folic Acid-Functionalized Carbon Nanotube Material

Abstract

A folic acid-functionalized carbon nanotube nanomaterial was prepared by immobilizing folic acid molecules on the carbon nanotubes through covalent bonds. The material was characterized using Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy. Fourier transform infrared spectroscopy confirmed that folic acid molecules were grafted on the carbon nanotube surfaces through the amide bonds between the carboxylic acid functional groups of the oxidized carbon nanotubes and the amine groups of the folic acid molecules. The folic acid molecules bonded to carbon nanotube surfaces led to appreciable changes in the morphology. By using currently obtained folic acid-functionalized carbon nanotube nanomaterial as electroactive material in a polyvinyl chloride membrane, a potentiometric copper (II)-selective sensor was developed. Membrane optimization studies showed that the composition exhibiting the best potentiometric properties was 4.0% (w/w) folic acid–carbon nanotube, 64.0% (w/w) o-nitrophenyl octylether, and 32.0% (w/w) polyvinyl chloride. The developed sensor displayed a linear response in the copper (II) concentration ranging from 1.0?×?10^–6 to 1.0?×?10^–1 M with a correlation coefficient of 0.9993 and a slope of 29.8?±?0.6?mV/decade of activity. The response time, detection limit, and pH working range were determined to be 4?s, 3.8?×?10^–7 M and 4.0–8.0, respectively. The developed sensor showed highly selective and satisfactory potentiometric response for the determination of copper (II) in a Turkish coin.     

Ethylenediamine and Hydroxyethylenediamine Complexes of Zinc(II): A Potentiometric Study of Composition and Stability

The equilibrium potential of saturated zinc amalgam is studied as a function of concentration of free ethylenediamine molecules, [en], in the region [en] 0.001–1 M in solutions of pH 9.5, 10.5, and 11.5. At the concentration of zinc(II) ions 2 × 10^–3 M and [en] = 1 M only simple trisethylenediamine complexes of zinc(II) form in all the solutions. At smaller [en] and pH 9.5 and 10.5, complexes Zn(en)₂ ²⁺ and Zn(en)₂OH⁺ are also present; these are complemented at pH 11.5 by Zn(en)₂(OH)₂ at [en] 0.005–0.1 M. Stability constants for these complexes are calculated.     

Potentiometric and Thermogravimetric Studies on Some Metal–Oxine–Sulphadrugs ternary Complexes

Formation constants (logK _MAL ^MA) of the mixed complexes of the type M–A–L (where M=Mn(II), Co(II), Ni(II), Cu(II), Ce(III), Th(IV), and UO₂(II); A=oxine and L=sulphamerazine or sulphadiazine) have been determined pH-metrically in 60% (v/v) ethanol–water mixture at 25°C and constant ionic strength (μ=0.1 M NaCl). The mode of chelation was ascertained by conductivity measurements. The stability sequence with respect to metal ions have been found to be Cu(II)>Ni(II)>Co(II)>Mn(II) and Th(IV)>UO₂(II)>Ce(III). CuAL ternary solid complexes have been prepared and characterized on the basis of elemental analysis and IR-spectroscopy. The thermal degradations of the prepared complexes are discussed in an attempt to assign the intermediate compounds formed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Calorimetric study and thermal analysis of [ErY(Ala)4(H2O)8](ClO4)6 (Ala=ALANINE)

A solid complex of rare-earth compounds with alanine, [ErY(Ala)₄(H₂O)₈](ClO₄)₆ (Ala=alanine), was synthesized, and a calorimetric study and thermal analysis for it was performed through adiabatic calorimetry and thermogravimetry. The low-temperature heat capacity of [ErY(Ala)₄(H₂O)₈](ClO₄)₆ was measured with an automated adiabatic precision calorimeter over the temperature range from 78 to 377 K. A solid-solid phase transition was found between 99 and 121 K with a peak temperature at 115.78 k. The enthalpy and entropy of the phase transition was determined to be 1.957 Kj mol^-1, 16.90 j mol^-1 k^-1, respectively. Thermal decomposition of the complex was investigated in the temperature range of 40~550°C by use of the thermogravimetric and differential thermogravimetric (TG/DTG) analysis techniques. The TG/DTG curves showed that the decomposition started from 120 and ended at 430°C, completed in three steps. A possible mechanism of the thermal decomposition was elucidated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Potentiometric determination of silver(I), palladium(II) and gold(III) in mixtures by use of an iodide-selective electrode

Two procedures are proposed for the potentiometric determination of Ag(I), Pd(II) and Au(III) in binary mixtures, by titration with potassium iodide solution, and use of a commercial iodide electrode as sensor. In the first procedure, two aliquots of the mixture are titrated, at pH 2.0 ± 0.2 and 9.0 ± 0.2, adjusted with dilute sulphuric acid and ammonia solution. At pH 2.0, the titrant reacts with both metals, whereas at pH 9.0, Ag(I) is the only reactant. The second procedure utilizes titration of two aliquots of the mixture in the presence and absence of a selective masking agent. The methods have been applied to the determination of these metals in some jewellery alloys.     

柱后衍生离子色谱法同时测定瓶装水中的碘酸根、亚氯酸根和溴酸根

水中的碘酸根、亚氯酸根和溴酸根是重要的消毒副产物,主要通过大体积浓缩后直接电导检测,或通过柱前或柱后化学反应将目标物转化成容易检测的物质后检测。本方法采用大体积进样柱后衍生紫外检测的分析方法,通过条件优化获得了较高的灵敏度和信噪比。利用一套自动分析系统,可以满足饮用水中痕量碘酸根、亚氯酸根、溴酸根的同时监测。碘酸根、亚氯酸根和溴酸根的检出限分别为0.5,0.4,0.1 μg/L。对于不同的加标样品,碘酸根、亚氯酸根和溴酸根的回收率分别为70.8%~98.0%,92.4%~100%和93.2%~104.1%。该方法应用于北京市场上的瓶装饮用水分析,结果显示瓶装纯净水中的碘酸根、亚氯酸根、溴酸根浓度均低于检出限,而瓶装矿泉水中碘酸根、溴酸根的最高含量分别达到9.4 μg/L和78.4 μg/L。     

Potentiometric study of the kinetics and equilibria of formation of chloroglycinate palladium(II) complexes from bis-glycinato palladium(II) complexes

The equilibria and kinetics of the reaction of Pd(gly)₂ complexes with hydrogen ions and chloride ions has been studied by a potentiometric method. The underlying idea of the method is the measurement of solution pH as a function of reaction time t using a glass electrode. The solutions used had the following initial compositions: xM Pd(gly)₂, xM Hgly, and 1 M NaCl with x = 1 × 10^?4, 5 × 10^?4, and 1 × 10^?3; initial pH₀ was from ～3.5 to ～4.4. The experimentally determined pH versus t dependences and the rate equation for a pseudo-second-order reaction were used to determine the equilibrium constant of formation of Pd(gly)(Hgly)Cl complexes from Pd(gly)₂ complexes and the observed rate constant for this reaction, k _obs. The dependence of k _obs on the pH of the acid solutions studied was assigned to a change in the sequence of the reactions of addition of a hydrogen ion and a chloride ion to the complex Pd(gly)₂.     

Lead-Selective Membrane Potentiometric Sensor Based on a Recently Synthesized Bis(Anthraquinone) Sulfide Derivative

Abstract

A new PVC membrane electrode for lead ions, based on bis[(1-hydroxy-9,10-anthraquinone)-2-methyl]sulfide as membrane carrier, was prepared. The sensor exhibits a Nernstian response for Pb²⁺ over a wide concentration range (5.6 × 10^?3-4.0 × 10^?6 M). It has a response time of about 30 s and can be used for at least 3 months without any divergence in potentials. The proposed membrane sensor revealed good selectivities for Pb²⁺ over a wide variety of other metal ions. It was used as an indicator electrode in potentiometric titration of lead ion.     

Facile Synthesis and Characterization of 5-[(3-Methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole and Its Potentiometric Sensor Application in a Polyvinyl Chloride Membrane for the Determination of Copper(II)

A novel Schiff base designated as 5-[(3-methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole was synthesized and characterized. A polyvinyl chloride-membrane potentiometric copper(II)-selective sensor was prepared by using the synthesized 5-[(3-methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole compound. The prepared polyvinyl chloride-membrane copper(II)-selective sensor exhibited very good selectivity and sensitive potentiometric response towards copper(II) ions compared to a wide variety of other cations. The sensor had a fast response time of <5?s, and showed a linear Nerstian behavior to copper(II) ions over a wide concentration range from 1.0?×?10^?5 to 1.0?×?10^?1 mol L^?1 with a slope of 29.2?±?0.7 and correlation coefficient of 0.9998. The prepared polyvinyl chloride-membrane copper(II)-selective sensor was used for 14 weeks without any significant change in its potentiometric response. The potentiometric response of the developed sensor was highly repeatable. Additionally, the developed sensor was used as an indicator electrode for the potentiometric titration of copper(II) ion with ethylenediaminetetraacetic acid. The sensor was also successfully applied to the direct determination of copper(II) ions in tap water, river water, and dam water samples.     

稀土钬及铒钇丙氨酸配合物的量热与热分析研究

合成了两种固态稀土丙氨酸配合物[Ho2(Ala)4(H2O)8]Cl6和[ErY(Ala)4(H2O)8](ClO4)6 (Ala为丙氨酸),用量热和热分析方法研究了这两种配合物的热力学性质.用全自动高精密绝热量热计测定了在78～377 K温区内的低温热容.对于[Ho2(Ala)4(H2O)8]Cl6,在214～255 K温区内发现一固-固相变,其相变温度为235.09 K.对于[ErY(Ala)4(H2O)8](ClO4)6,在99～121 K温区内也发现一固-固相变,其相变温度为115.78 K. [Ho2(Ala)4(H2O)8]Cl6固-固相变焓为3.02 kJ• mol－1,相变熵为12.83 J•K－1•mol－1； [ErY(Ala)4(H2O)8](ClO4)6 固-固相变焓为1.96 kJ•mol－1,相变熵为16.90 J•K－1•mol－1.同时,用TG技术在40～800 ℃温区研究了两配合物的热稳定性.由TG/DTG曲线分析可知, [Ho2(Ala)4(H2O)8]Cl6从80 ℃到479 ℃热分解分两步完成, [ErY(Ala)4(H2O)8](ClO4)6从120 ℃到430 ℃热分解分三步完成.     

Calorimetric investigation of temperature effect on the interaction between poly(ethylene oxide) and sodium dodecylsulfate in water

The interaction of four poly(ethylene oxides), with molar masses of 1500, 3350, 10 000 and 100 000 g mol⁻¹ with sodium dodecylsulfate, at 15, 25, 35 and 65 °C was investigated by isothermal titration calorimetry. No significant change of the critical aggregation concentration values or of the amount of surfactant bound was observed within this temperature range. The profiles for the variation of the observed enthalpies with surfactant concentration, however, are quite different for the four studied temperatures, what has been interpreted as a consequence of a change in the mode of poly(ethylene oxide) (PEO) interaction with sodium dodecylsulfate (SDS) micelles within this temperature range.     

Potentiometric and thermodynamic studies of 2-mercapto-5-(2-hydroxynaphthylideamino)-1,3,4-thiadiazole and its metal complexes

Summary Proton-ligand dissociation constant of 2-mercapto-5-(2-hydroxynaphthylideamino)-1,3,4-thiadiazole (MHT) and the stepwise stability constants of its metal complexes were determined potentiometrically in 40 mass/mass% ethanol-water mixture containing 0.1 M KCl. The stabilities of the complexes follow the order: Cu²⁺>Ni²⁺>Co²⁺>Mn²⁺. The dissociation constant (pK^H) of MHT and the stability constants (logK) of its metal complexes were determined at different temperatures and the corresponding thermodynamic parameters were calculated and discussed. The proton dissociation process is non-spontaneous, endothermic and entropically unfavoured. The formation of the metal complexes was found to be spontaneous, endothermic and entropically favoured.     

Determination of Dysprosium(III) Ion in Soil and Sediment Samples by an Original Potentiometric Dysprosium(III) Membrane Sensor

Abstract

A PVC membrane electrode for dysprosium(III) [Dy(III)] ions was constructed, having its basis on benzoxazoleguanidine (BG) as a suitable ionophore. The sensor presents a linear dynamic range of 1.0 × 10^?6–1.0 × 10^?1 M, with a Nernstian slope of 19.5 ± 0.4 mV decade^?1 and a detection limit of 4.7 × 10^?7 M. The response time is quick (less than 10 s). It can be used in the pH range of 3.3–8.4, and its duration is at least 2 mo without any considerable, noticeable potential divergence. The recommended sensor revealed comparatively good selectivity with respect to most alkali, alkaline earth, some transition, and heavy metal ions. It was successfully employed as an indicator electrode in the potentiometric titration of Dy(III) ions with EDTA. The membrane sensor also applied to the determination of concentration of Dy(III) ions in soil and sediment samples. Validation with certified reference materials (CRMs) was also carried out.     

Potentiometric Anion Selectivity and Analytical Applications of Polymer Membrane Electrodes Based on Novel Mn(III)‐ and Mn(IV)‐Salophen Complexes

New Mn(III)‐L and Mn(IV)‐L complexes were prepared from the highly lipophilic salophen ligand (L): phenol 2,2′‐[(4,5‐dimethyl‐1,2‐phenylene)bis[(E)‐nitrilomethylidyne]]bis[4,6‐bis(1,1‐dimethylethyl). The prepared complexes were fully characterized and used for the construction of thiocyanate membrane electrodes. Optimized membrane electrodes contained 33.0 mg PVC, 66.0 mg o‐nitrophenyloctylether, 50 or 5 (mole %) tetrakis(trifluoromethyl)phenyl borate and 1 mg Mn(III)‐L (sensor 2) or Mn‐(IV)‐L (sensor 12), respectively. Such electrodes exhibited linear responses toward thiocynate in a concentration range of 10^?1–10^?5 M and detection limits of 8.3×10^?6, 8.9×10^?6 M for sensor 2 and 12, respectively. Optimized membrane electrodes exhbited high selectivty toward thiocayante compared to more lipophilic anions. The observed thiocyanate selectivity of the optimized membranes was confirmed by formation constant calculations for Mn(III)‐L and Mn(IV)‐L with SCN^?, β=10^14.1 and 10^12.5, which was measured potentiometrically using the sandwich membrane method. Furthermore, computational study using DFT calculations was performed to at DFT/B3LYP level of theory to confirm the observed selectivity data. The response times were 3 and 0.5 min for low and high concentrations. The lifetimes of the optimized electrodes were ～4–6 weeks. The analytical utility of the optimized membrane electrodes was demonstrated by the analysis of thiocyanate level in different saliva samples.