Ionic equilibria in alkaline aqueous solutions of metal complex salts

A thermodynamic analysis of the formation conditions of metal hydroxides was performed. The areas of stable formation of metal hydroxide precipitates in the coordinates pH-metal concentration, including also solutions containing various kinds of complexing agents, were evaluated. With the precipitation of cadmium hydroxide as example, X-ray phase analysis confirmed the formation of metal hydroxide in the chemical composition areas where its formation is predicted by a thermodynamic analysis.     

On-line dialysis of some metal ions and metal complexes

The effect of ionic strength, pH and complexing ligands on the dialysis of metal ions, particularly zinc(II), through cellulose acetate membranes, was studied under flow conditions. The dialysis factor, which depends on both the mass transfer and the membrane permeability, was found to be independence of ionic strength in the interaval 0.05–0.3 M and to increase only slightly with pH 4.6 and 7.0. Some common buffer constituents had no effect, but chloride and calcium ions affected the transfer rates. The rate of transfer of the ligands histidine, NTA and EDTA was of the same order of magnitude as that of the metal ions. The transfer rate of the Ni(II)-EDTA complex was the same as that of a mixture of Ni(II) and EDTA. Generally, addition of the chelating agents decreased the metal-ion transfer rates. Partition coefficients between the membrane polymer and the buffers were evaluated and compared with the dialysis factors and there were significant differences with regard to the range of variation, effect of concentration and pH-dependence. The time scale of uptake or release of metal ions by the polymer is much longer than that of a steady-state transfer in dialysis. Partition and dialysis may not be directly related to each other.     

Complexation ion-exchange chromatography of some metal ions on papers impregnated with Ti(IV)-based inorganic ion exchangers

The chromatographic behavior of 40 metal ions is studied on titanium (IV) arsenate, titanium (IV) phosphate-, titanium (IV) molybdate-, titanium(IV) tungstate-, and titanium(IV) selenite-impregnated papers in 0.1M oxalic, citric, and tartaric acid as mobile phases. Similar studies are carried out on Whatman No. 1 papers for comparison. The ion-exchange capacity of these papers is determined, and their selectivity for different cations is discussed. The mechanism of migration is explained in terms of ion-exchange, precipitation, and adsorption. The prediction of elution sequence from RF values is also checked. The average Ri is found to be almost linearly dependent on the charge of the metal ions. The effect of the pKa of complexing acids on average RF values of 3d series metal ions is explained. A number of binary and ternary separations are achieved.     

混合稀土离子的毛细管电泳电导法分离检测

采用高效毛细管电泳电导检测法分离检测了稀土离子。以醋酸-醋酸钠为背景电解质,4-吗啉乙磺酸（MES）为络合剂,在24kV的高压下,7种稀土离子得到子较好的分离。考察了背景电解质的pH和浓度,络合剂的浓度,分离电压等对稀土离子分离的影响。在选定的实验条件下,7种烯土离子在10min内守成分离检测。     

Eigen kinetics in surface complexation of aqueous metal ions

The mechanism of chemisorption of aqueous metal ions at surfaces has long been a topical issue in such fields as soil chemistry and bioenvironmental science. Here it is quantitatively demonstrated for the first time that release of water from the inner hydration shell is the rate-limiting step in inner-sphere surface complexation. The reactive intermediate is an outer-sphere complex between metal ion and surface site, with an electrostatically controlled stability defined by Boltzmann statistics. Using tabulated dehydration rate constants for metal ions, the resulting scheme allows for prediction of rates of sorption of aqueous metal ions at any type of complexing surface.     

Laser flash photolysis of spiropyran in the presence of metal ions in solution

Conclusions Intermediate trans isomers of spiropyran with different stability participate in the reaction of complexing of spiropyran with metal ions. Several types of complexes are formed. A scheme of the reaction of complexing of spiropyran with metal ions is proposed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2243–2250, October, 1988.     

Characterization of metal cations-complexing polymer films interactions followed with anodic stripping voltammetry

The complexing ability of thin poly(3-pyrrol-1-ylpropyl)malonic acid films coated onto glassy carbon disc electrode surfaces was evaluated towards Pb(II) and Cu(II) ions, using the chemical preconcentration-anodic stripping method. The affinity of these metal cations for the complexing film modified electrodes and their maximal surface coverage rate could be evaluated from a Langmuir isotherm model coupled to the chemical preconcentration-anodic stripping technique. Isothermal studies conducted between 293 and 308 K allowed to estimate enthalpy and entropy variations associated to the metal sorption, which expectedly proved to fit chemisorption processes. As judged from the estimated binding constants, Pb(II) ions turned out to present a higher affinity for the functionalized surface than the smaller Cu(II) species. The mobilization of a higher number of malonic acid units per metal cation upon complexation of Pb(II), as compared to Cu(II), is however believed to account for the estimated lower Pb(II) surface coverage. The combination of the Langmuir isotherm model to the chemical preconcentration-anodic stripping technique is thus revealed to be an efficient method to characterize the complexing ability of complexing film electrode surface.     

Ion-exchange equilibrium distribution studies of some metal ions in nitrite media

Ion-exchange equilibrium distribution of some metal ions has been studied in nitrite media, with cation- as well as anion-exchangers. The distribution coefficients (K(D)) show the utility of a new nitrite medium which is a complexing medium for most transition metal ions giving anionic complexes in aqueous solution. Similar studies have been performed in aqueous ethanol. Increase in the concentration of ethanol led to increased complex formation and changed K(D) values.     

Ion-interaction chromatographic separation of metal cations in the presence of complexing agents

The mechanism of the separation of selected divalent metal cations (Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺, Mn²⁺, Fe²⁺ and Pb²⁺) by ion-interaction chromatography (IIC) in the presence of complexing agents has been investigated; the dependence of the retention of the analyte on the concentration of the complexing ligand has been studied. Separations have been obtained on an octadecyl-bonded silica column, mobile phases containing an ion-interaction agent (octane sulfonate), eluting cations (Na⁺ ions) and a complexing ligand (oxalate anions).     

Determination of metal ions by liquid chromatographic separation of their 2-acetylpyridine-4-ethyl-3-thiosemicarbazone chelates

A new thiosemicarbazone was prepared, characterized, and used as a complexing reagent for the chromatographic separation and determination of metal complexes by reverse-phase HPLC. The reagent was sufficiently soluble in methanol-water solutions for metal ions to be complexed in this aqueous organic phase, without need for extraction. Many variables affected the retention times of the metal complexes. Several metals were determined selectively by complexation with the reagent and chromatographic separation of the complexes. Interference effects from other metal ions were also investigated.     

Separation of metal ions by capillary electrophoresis with a complexing electrolyte

Excellent separations of metal ions can be obtained very quickly by capillary electrophoresis provided a weak completing reagent is incorporated into the electrolyte to alter the effective mobilities of the sample ions. Indirect photometric detection is possible by also adding a UV-sensitive ion to the electrolyte. Separations are described using phthalate, tartrate, lactate or hydroxyisobutyrate as the complexing reagent. A separation of twenty-seven metal ions was achieved in only 6 min using a lactate system. A mechanism for the separation of lanthanides is proposed for the hydroxyisobutyrate system.     

Chemical analyses of heavy metal contamination in sediments of the Venice Lagoon and toxicological implications

Heavy metals are extracted from sediments using 1 M HCl; then, solutions are neutralised with 1 M NaOH, to fit the conditions suitable for the Vibrio Fischeri test. In the neutralised solutions different percentages of initial metal concentration are present, depending on the individual solubilities. The chemical investigation of the metal fraction extracted from the sediment with this procedure and the different metal bioavailability depending on the presence of natural complexing agents are the subject of this work. The results obtained confirm the good agreement between heavy metal fraction extracted using 1 M HCl and the anthropogenic component in the sediment. The use of voltammetric techniques, and the addition of low molecular weight humic acids into extracts show the ability of natural complexing agents in affecting heavy metal bioavailability and toxicity.     

Ion-exchange thin-layer chromatography of metal lons in organic solvent — Hydrochloric acid — Complexing agent media

Summary Thin-layers of strongly basic or strongly acidic ionexchange resins (Dowex 1 or Dowex 50), mixed with a plain cellulose, Avicel SF, have been used to investigate the chromatographic behaviour of 40 metal ions in acetic acid — hydrochloric acid — complexing agent media. The CIESE (combined ion-exchange-solvent extraction) effect, proposed by Korkisch, is noticed for scandium and thorium in the anion-exchange system involving trioctylphosphine oxide (TOPO) as the complexing agent, the system providing a basis on the specific separation of both elements. In the cation-exchange system involving TOPO, the metal ions are distributed chromatographically, so that the system allows multicomponent separations to be carried out. The system also reveals the CIESE effect for zirconium and hafnium.     

Evaluation of micromolar compleximetric titrations for the determination of the complexing capacity of natural waters

The titration of micromolar levels of complexing agents with metal ion titrants, and voltammetric methods to locate the equivalence point, has been evaluated experimentally and theoretically. Both anodic stripping voltammetry and differential pulse polarography give systematically low results if labile metal ions are used as titrants. Low-temperature (0 °C) dual-cell anodic stripping voltammetry greatly minimizes the effects of metal complex lability but the mercury film electrodes deteriorate rapidly because of temperature cycling. A micromolar compleximetric titration with a voltammetric end-point is not a practical method for determining the complexing capacity of natural waters.     

Concentration and separation of trace metals with an arsonic acid resin

Macroporeus arsonic acid resins with different pore sizes and surface areas were prepared and the properties compared. One of the resins was used for concentration of trace metal ions from dimineralized water, tap-water, and sea-water. The effect of pH and complexing agents on the recovery of metal ions was studied. A method for separation of uranium(VI) and thorium(IV) from each other and from other metal ions was developed.     

Separation of transition metals in nonaqueous media with capillary electrophoresis

The separation of transition metal Ni2+, Cu2+, Co2+, Zn2+, Cd2+ and Fe3+ in methanol was investigated by using different types of organic acids as complexing agents. In pure methanol, the weaker and simpler acetic, propionic, butyric and valeric acids could enhance metal ions selectivity by increasing acid concentration and metal ions could be separated with high efficiency. However, hydroxycarboxylic acids obviously made separation efficiency worse. The effect of mixed organic acids, mixture solvent (methanol-acetonitrile, methanol-water) on metal ions separation was discussed further. The advantages of using nonaqueous solvent over aqueous for metal ions separation were shown finally.     

Preparation of polymer-coated electrodes containing metal ions complexing sites by electropolymerization of 2-mercaptobenzimidazole and 2-mercaptobenzothiazole on glassy carbon

The possibility of producing polymer-coated electrodes containing complexing agents capable of collecting metal ions was investigated. The organic ligands 2-mercaptobenzimidazole and 2-mercaptobenzothiazole were used as monomers for electropolymerization on glassy carbon electrodes. The electroanalytical applicability of the modified electrodes was evaluated for Hg²⁺ ions, by applying a chemical preconcentration step with subsequent measurement by differential pulse voltammetry. The influence of some electropolymerization parameters, such as scan rate, monomer concentration and the number of cyclic scans, on the voltammetric response of mercury(II) was studied. A 5 min preconcentration period allowed the detection of 0.08 mg/L (4.0 × 10⁻⁷ mol L⁻¹) mercury.     

Redox behavior of metal tetraphenyl porphins

The first half-wave potentials of reduction (on a mercury-film electrode) and oxidation (on a glassycarbon electrode) of tetraphenyl porphins of Al, Ga, In, Tl, and Sn in nonaqueous media are obtained from voltammograms. It is shown that the porphin ligand and the complexing metal take part in these reactions. The assumption that inductive parameters of metal ions can be used in predicting redox potentials of metal tetraphenyl porphins is confirmed experimentally     

New Electrodes with Membranes Based on Semiconductor Compounds of the AIIIBV Type

The characteristics of new electrodes with semiconducting membranes based on gallium arsenide and gallium antimonide were studied in solutions of metal salts, halides, and complexing agents. The proposed electrodes can be used as indicator electrodes in acid–base, precipitation, and complexometric potentiometric titration.     

Reverse flow injection analysis of complexing agents and its application to estimation of complexing capacity

A redox reaction of copper(II) with iron(II) proceeds slowly in the presence of neocuproine, although the reaction would not take place in its absence. This reaction is accelerated by the presence of complexing agents such as EDTA, DTPA, CyDTA, EDTA-OH, NTA, citrate, pyrophosphate, producing a copper(I)-neocuproine complex (lambda(max) = 454 nm). A reverse flow injection analysis (r-FIA) method is presented for the determination of trace amounts of complexing agents by measuring the increase in absorbance at 454 nm. Complexing agents at the 10(-6)M level can be determined at a rate of 120 samples/hr. By using this r-FIA system, a new procedure for the measurement of complexing capacity with metal ions such as Al(III), Cu(II), Zn(II), Cd(II) and Pb(II) has been developed. Complexing capacity for each metal ion can be measured at a rate of 120 samples/hr.