Volumetric,Viscosity and Self-Diffusion Coefficient Studies of [18-Crown-6:M]A Complexed Species in Water at 298.15 K

Density and viscosity measurements were made for aqueous solutions of electrolytes containing 18-crown-6 (18C6) at 298.15 K. A method is proposed to extract the volumetric and viscosity data of the [18C6:M]A complexed species in aqueous solutions from ternary mixtures using the thermodynamic equilibrium constant values at 298.15 K. The apparent molar volume of the [18C6:M]A complexed species have been estimated for these binary solutions. Further, the viscosity data thus obtained were subjected to analysis using the Jones-Dole equation to get viscosity A- and B-coefficients of complexed ions in water. The hydration number and molecular radius of the hydrated complexes in water have been estimated. It was observed that hydration of the complexed ion is strongly influenced by the charge density of the metal ions in the complexed state. The self-diffusion coefficient and correlation time values for the complexes in water were calculated using viscosity data, which indicated that diffusion of complexed species was faster than that of the host ligand 18C6 (D_3d structural entity) in water at 298.15 K. It was suggested that the ionic radii estimated in this work for large hydrophobic cations can be of use in studying electrostatic and hydrophobic interactions especially in aqueous solutions.     

Synthesis, physical studies and uptake behavior of: copper(II) and lead(II) by Schiff base chelating resins

Two new chelating resins possessing multiple functional groups capable of coordinating with several metal ions are reported. The resins were synthesized by condensing Schiff bases derived from 2-aminophenol, 2-hydroxy-5-chloroaniline and terephthaldehyde with formaldehyde in an alkaline medium. The effects of pH and contact time of the Cu(2+) and Pb(2+) in aqueous solutions on the uptake behavior of the resins were studied. The metal ion uptake behavior of the resins was investigated by the batch method. Both the uptake and the selectivity of the resins towards the investigated metal ions were related to the structure of the resins, type of the metal ion and the uptake conditions. The resins showed maximum uptake capacity for Cu(2+) and Pb(2+) at pH 10. Cu(2+) was seen to undergo preferential adsorption in separate and mixture solutions of Cu(2+) and Pb(2+). Kinetic studies for the resins using Langmiur equation were also performed. The Schiff base monomers and their formaldehyde resins were characterized by elemental analyses, FTIR and (1)H NMR spectroscopy. The thermal stability of the resins was studied using TGA/DTG analysis.     

Ca2+‐complex stability of GAPAGPLIVPY peptide in gas and aqueous phase,investigated by affinity capillary electrophoresis and molecular dynamics simulations and compared to mass spectrometric results

Strong, sequence‐specific gas‐phase bindings between proline‐rich peptides and alkaline earth metal ions in nanoESI‐MS experiments were reported by Lehmann et al. (Rapid Commun. Mass Spectrom. 2006, 20, 2404–2410), however its relevance for physiological‐like aqueous phase is uncertain. Therefore, the complexes should also be studied in aqueous solution and the relevance of the MS method for binding studies be evaluated. A mobility shift ACE method was used for determining the binding between the small peptide GAPAGPLIVPY and various metal ions in aqueous solution. The findings were compared to the MS results and further explained using computational methods. While the MS data showed a strong alkaline earth ion binding, the ACE results showed nonsignificant binding. The proposed vacuum state complex also decomposed during a molecular dynamic simulation in aqueous solution. This study shows that the formed stable peptide–metal ion adducts in the gas phase by ESI‐MS does not imply the existence of analogous adducts in the aqueous phase. Comparing peptide–metal ion interaction under the gaseous MS and aqueous ACE conditions showed huge difference in binding behavior.     

Chelating Sorbents Prepared by the Modification of Silica Gel, Lichroprep RP-8 and Lichroprep RP-18 with Calcon and Their Application in the Analysis of Some Metal Ions

 Two new chelating sorbents for metal ions were prepared by the impregnation of chemically modified silicas LiChroprep RP-8 and RP-18 with ion pairs composed of the cation of Aliquat 336 and the anion of Calcon. The sorbents were compared with an analogous sorbent with a plain silica carrier containing the same ion pairs. A hypothesis for binding this ion pair by the surfaces of the applied carriers was presented. A higher stability of the two sorbents in comparison with that of the plain silica chelating sorbent was demonstrated. The sorbents obtained were applied for chromatographic separations of some chosen mixtures of some metal ions and for additional purification of aqueous solutions of alkali metals from trace amounts of heavy metals. The multiple use of the sorbents based on RP-8 and RP-18 in sorption–desorption processes of metal ions without deterioration of their sorption capacities was demonstrated. Received March 8, 2000. Revision March 5, 2001.     

Analytical application of surface-affinity polymerized vesicular membranes to trace metal analysis by electrothermal atomic absorption spectrometry

The affinity of anionic polymerized vesicular membranes for metal cations in aqueous solutions is explored in terms of metal ion extraction and preconcentration. The method is based on the coordination of metal ions on the surface of charged polymerized vesicles via intra-vesicular complexes. These are causing changes in the selectivity, reactivity and inter-vesicular bridges which facilitate the aggregation of polymerized vesicles promoting phase separation. An analytical demonstration is shown by the optimization of the experimental conditions that enable the determination of antimony (III) in natural waters. The analytical features of the method including detection limits, precision and analytical recoveries from spiked natural water samples suggest that polymerized vesicular membranes can be a promising alternative to surfactant-mediated extractions of metal ions from aqueous matrices.     

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.      

Synthesis and properties of new N,S-containing fibrous ion exchangers

New N,S-containing fibrous ion exchangers were prepared by polymer-analogous transformations of Nitron fiber, involving amination with polyethylenepolyamines (ethylenediamine and diethylenetriamine), followed by the reaction of the aminated fiber with carbon disulfide. The materials obtained efficiently take up silver ions from multicomponent aqueous solutions of metal ions and from dilute solutions containing calcium ions.     

Self-motion of a phenanthroline disk on divalent metal ion aqueous solutions coupled with complex formation

The self-motion of a 1,10-phenanthroline disk on divalent metal ion aqueous solutions was investigated as a simple autonomous motor coupled with complex formation. The characteristic features of motion (continuous and oscillatory motion) and their concentration regions differed among metal ions, and the frequency of oscillatory motion depended on the temperature of the aqueous solution. The nature of the characteristic motion is discussed in relation to the stability constant of complex formation between phenanthroline and a metal ion, and the difference in surface tension between phenanthroline and its metal complex as the driving force.     

双波长分光光度法同时测定溶液中的硝酸根和碘离子

食品和环境样品中往往同时含有硝酸根和碘离子,用紫外分光光度法直接测定硝酸根或碘离子时,二者相互干扰。为此建立了主、次波长分别为220.0、231.5 nm的等吸收点双波长紫外分光光度法测定溶液中的硝酸根和共存的碘离子。当溶液中硝酸根的浓度在0~0.12 mmol/L的范围内,碘离子的浓度在0~0.10 mmol/L的范围内时,主、次波长下的吸光度差值A220-231.5与溶液中硝酸根的浓度 呈良好线性关系,线性方程为A220-231.5 = 2.9958 0.0016（R2 = 0.99994）;其中A220 (NO3-) = 3.6099 0.0084（R2 = 0.99994）,利用吸光度的加和性：A220 (I-) = A220 - A220 (NO3-) = 10.7394 0.0029（R2 = 0.99994）,间接得到碘离子含量 。硝酸根和碘离子的平均相对标准偏差分别为0.6%、0.2%,回收率分别为99.5~102%、99.9~100%。方法简便快捷,可用于溶液中微量硝酸根和碘离子的同时测定。     

Transfer of actinide ion at the interface between aqueous and nitrobenzene solutions studied by controlled-potential electrolysis at the interface

A novel electrochemical method based on controlled-potential electrolysis has been developed for the elucidation of the ion transfer at the interface between two immiscible electrolyte solutions (ITIES). A relationship between the applied interfacial potential (E_app) and the amount of the ion transferred (A_tr) was investigated after an electrolytic equilibrium was attained by controlled-potential electrolysis. The A_tr was determined chemically or radiometrically instead of by current measurement. It was found that (i) controlled-potential electrolysis was applicable to the study of the transfer of such hydrophilic ions as transition metal ions which gave no appreciable current within the potential window in voltammetry or polarography at ITIES, (ii) controlled-potential electrolysis in combination with a sensitive analytical method enabled a study of the transfer reaction of an ion of very dilute concentration, and (iii) even when the transfer reaction of an ion was irreversible or quasi-reversible, a standard ion transfer potential could be determined by controlled-potential electrolysis without using a kinetic parameter. The controlled-potential electrolysis method developed was applied to the transfer reactions of actinide ions such as UO₂ ²⁺ and Am³⁺ from aqueous solution to nitrobenzene solution in the absence or presence of an ionophore facilitating the transfer. The Gibbs energy for the transfer of actinide ion and a stability constant of the complex between an actinide ion and the ionophore in nitrobenzene solution were determined from log D versus E_app plots (D the ratio of the concentration of the ion in nitrobenzene solution to that in aqueous solution). The feasibility of controlled-potential electrolysis as a method for electrolytic separation of actinide ions is discussed.     

高温及超临界条件下 MgCl2与CaCl2水溶液中离子水化与缔合的量子化学计算

对NaCl等碱金属水溶液的研究表明,室温条件下,离子在溶液中以水合形式存在,而在高温及超临界时,阴阳离子将结合成为离子对．采用量子化学计算,研究了MgCl2与CaCl2水溶液中水化与缔合的情况．通过Gaussian98软件包计算了阳离子的水化自由能以及离子对的生成能,从而获得水合离子与离子对的热力学稳定性及其随温度、压力的变化情况．通过比较热力学稳定性,考察了两种溶液中水化与缔合的变化情况．研究结果表明,MgCl2与CaCl2水溶液中离子水化与缔合的变化趋势与碱金属溶液基本一致,但是存在一个过渡区域,该区域内离子对与水合离子共存,因此需要采用不同于碱金属溶液的方法处理MgCl2与CaCl2水溶液．     

Analysis of metal complex azo dyes by high-performance liquid chromatography/electrospray ionization mass spectrometry and multistage mass spectrometry

Five metal complex azo compounds were analyzed using negative-ion electrospray ionization mass spectrometry (ESI-MS). Mass spectra of all compounds yield intense peaks corresponding to [M - H](-) ions without any fragmentation, where M denotes the neutral compound with a proton as the counterion. Under collision induced dissociation (CID) conditions, structurally important fragment ions were studied using the ion trap analyzer with a multistage mass spectrometry (MS(n) facility. Synthesized compounds with (15)N atoms in the azo group facilitated the fragmentation pattern recognition. A reversed-phase high-performance liquid chromatography (HPLC) method using 5 mM ammonium acetate in 70% aqueous acetonitrile as mobile phase was developed making possible the separation of all complex compounds tested. The lower detection limits of the ESI-MS method are in the range 10-20 ng of each compound. The HPLC/ESI-MS method makes possible the monitoring of ligand exchange in aqueous solutions of metal complex azo dyes, and also investigation of the stabilities of the complexes in solution. Copyright 2000 John Wiley & Sons, Ltd.     

Membrane-based solvent extraction for selective removal and recovery of metals

A membrane-based solvent extraction process was developed for selective removal and recovery of metals from aqueous solutions. The process utilizes microporous membranes as an interface between an aqueous solution and organic solvents containing liquid ion exchangers. Metal ions are transported from the aqueous solution to the organic phase at the interface created in the pores of membrane. The organic solvent, which is loaded with metal ions in the extraction module, is regenerated in contact with the stripping solution in the stripping module. One important feature of this process is the stability of the membrane system, which results from using an aqueous—organic separator to remove aqueous solution from the organic circulating line. This process was evaluated for enrichment of copper using solvents containing LIX 64N. The process is applicable to selective recovery of metals from ore leachates or metal-containing wastewater.     

Selective separation and extraction of copper(II), iron(II,III), and Cerium(III,IV) ions from aqueous solutions by electroflotation method

Possibility of the electroflotation separation and extraction of cerium(II, IV), copper(II), and iron(II, III) from aqueous solutions is demonstrated. The optimal pH value and the concentration ratio of ions of the metals being separated, at which their electroflotation separation and extraction from aqueous solutions is the most efficient, was determined. It was shown that the electroflotation method is promising for selective separation and extraction of metal ions with various hydrate-formation pH values from aqueous solutions.     

Electrophoretic mobility study on ion-ion interactions in an aqueous solution.

Ion-ion interactions between anions and their pairing ions in aqueous solutions were studied through the measurements of electrophoretic mobilities of analyte ions in capillary zone electrophoresis, where the electrophoretic method for the analysis of ion association reaction is shown to be more useful than the conductometric method widely used in the analysis of the reactions. The electrophoretic mobility of monovalent inorganic anions was almost identical even when the concentrations of alkali metal ions and quaternary ammonium ions in the migrating solution were varied up to 15 mM. On the other hand, the electrophoretic mobility of organic anions, such as monovalent and divalent anions, decreased with increasing concentrations of quaternary ammonium ions. Changes in the electrophoretic mobilities were analyzed by a non-linear least-squares method giving ion association constants. The results indicate that the proposed method is applicable to the analysis of such reactions to give the mobility change. The ion association constants obtained in an aqueous solution were related to the extraction constants of the ion associates, and the contributions of the association process and the distribution process were clarified.     

Adsorption Properties of Metal Ions Using Alumina Nano-Particles in Aqueous and Alcoholic Solutions

Different metal ions in aqueous and alcoholic solutions were adsorbed on alumina nano-particles prepared by the sol-gel method. The flocculation of the alumina sol was induced by the addition of different metal ions in solution. The flocculation kinetics was obtained by monitoring the particle growth with time using dynamic light scattering. These experiments were carried out following two different methods: a) the multiple injection method which consist in adding small amounts of metal ions until the critical flocculation concentration was reached and b) single injection method where an amount of metal ions equal to the critical flocculation concentration is added all in one shot. The efficiency of metal adsorption was determined by Atomic Absorption Spectroscopy.     

Extraction of rare-earth,yttrium, and scandium perchlorates by podands bearing diphenylphosphorylacetamide terminal groups

Partition of trace amounts of metal (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc) perchlorates was studied between aqueous HClO₄ solutions and dichloroethane solutions of phosphorus podands bearing two Ph₂P(O)CH₂C(O)NH-terminal groups linked via di-and triethylene glycol spacers. The stoichiometry of extracted complexes was determined. The efficiency of metal ion recovery to the organic phase was studied as a function of aqueous HClO₄ concentration and nature of the organic solvent. The compounds synthesized have higher metal extraction capacities in HClO₄ solutions than (dibutylcarbamoyl)diphenylphoshine oxide. The utility of macroporous polymer sorbents impregnated by these podands for extracting and concentrating rare earth(III) and scandium(III) ions from aqueous perchlorate solutions was demonstrated.     

Investigation of Metal Ion Removal Selectivity Properties of the Modified Polyacrylamide Hydrogels Prepared by Transamidation and Hofmann Reactions

Modified crosslinked polyacrylamides having different functional groups prepared by transamidation reaction in aqueous and non‐aqueous medium and by Hofmann reaction were used as chelating agents for removal of Cu(II), Cd(II) and Pb(II) ions from aqueous solutions at different pH values. Under non‐competitive conditions, polymers adsorbed different amounts of metal ions, depending on their functional groups and swelling abilities. The metal ion adsorption capacities of polymers changed between 0.11–1.71 mmol/g polymer. Under competitive conditions, while the polymers having mainly secondary amine groups were highly selective for Cu(II) ions (99.4%), those having mainly secondary amide and carboxylate groups have shown high selectivity towards Pb(II) ions (99.5%). The selectivity towards Cu(II) ion decreased and Pb(II) ion selectivity increased by the decrease of the pH of the solutions. The high initial adsorption rate (<10 min) suggests that the adsorption occurs mainly on the polymer surface. A regeneration procedure by treatment with dilute HCl solution showed that the modified polymers could be used several times without loss of their adsorption capacities.     

标准溶液测量不确定度的评定

对标准溶液测量不确定度进行合理评定，充分估计分析不确定度的来源，从量值检验时考虑到影响不确定度的各种因素，测量方法的不确定度．配制时考虑到影响不确定度的各种因素以及标准溶液的不均匀性和在有效期内的变动性所引起的不确定度等方面进行综合分析，得出其扩展不确定度。并以镍标准溶液为例作实际分析。     

Adsorption properties of a nanostructured hybrid material containing aluminium towards some metal ions

In the present work the adsorption of some transition metal ions from aqueous solutions on a silica-based nanostructured hybrid material modified by aluminium was investigated. The novel organic-inorganic material was synthesized via a sol-gel method through hydrolysis and co-condensation reactions. Its structure was characterized by means of SEM, XRD and FTIR. Based on the data obtained the most probable cross-linking mechanism for the derived xerogel was proposed. The characterization of its texture parameters was carried out by low-temperature adsorption of nitrogen. The adsorption properties of this material with respect to Cu(II), Cr(III) and Pb(II) ions from single-component aqueous solutions and multi-component aqueous solutions containing also Cd(II) and Fe(III) were evaluated. The effect of contact time, acidity of initial solutions and metal ion concentrations was investigated using the batch method. Pseudo-first order, pseudo-second order and intraparticle diffusion models were used to analyze kinetic data. In all cases the adsorption was significantly affected by the pH value. Equilibrium modelling data were fitted to linear Langmuir, Freundlich and Dubinin-Radushkevich models. Best fit was observed for Langmuir model, which showed determination coefficients greater than 0.992 for all ions studied. The maximum adsorption capacities for single- and multi-component adsorption were calculated.