Convolution-deconvolution cyclic voltammetric equilibria study on cadmium(II)-L-histidinate in aqueous solutions

POLAG computer programme was employed for processing convoluted-deconvoluted cyclic voltammetric data to study cadmium(II)-L-histidinate system. This was performed in 0.1 mol/dm(3) NAClO(4) aqueous solution at different pH's at 298K. The results show that the reduction of cadmium(II) and its complexes proceeds via a reversible and diffusion-controlled wave of two electrons at the entire range of pH. The system was studied at two ranges of pH (6.73-7.44 and 8.53-8.92). It was evident that the system at the first range of pH is well described by the presence of a mixture of binary complexes, [Cd(HisO.H)], [Cd(HisO.H(2))(2)] and a ternary one [Cd(HisO.H)(HisO.H(2))]. For the second pH range, it was revealed that the most likely model corresponds to the presence of a mixture of [Cd(HisO)(2)] and [Cd(OH)] species. The overall stability constants were computed. The structure of the detected complexes was discussed on the basis of ligating sites of histidine.     

Target transform fitting in a voltammetric study of metal complexation

In this work target transform fitting (TTF) is proposed as a hard-model based data analysis method to analyze differential pulse polarograms recorded in a successive metal complexation system. In such cases, equations for both complexation equilibria and shape of the differential pulse polarogram for individual species are available. Utilizing TTF to fit these models in separate stages, stability constants and E_1/2 values of species were estimated. In the first stage, E_1/2 values of all species were acquired using the shape-equation of voltamograms and projection of a test vector into the row space of data matrix. In the second stage, using equations derived from relationships among species’ concentrations in complexation equilibria and a non-linear parameter fitting algorithm, the optimum values of overall formation constants were estimated. Finally, rank annihilation (RA) method was employed for calculation of diffusion coefficients. In spite of the fact that proposed method is a hard-model based approach, obtained results show that analysis can be performed correctly even in presence of unknown species. The reliability of the method was tested analyzing simulated data and also polarograms obtained from Cd(II) and 1, 10-phenanthroline complexation system. This experimental system yields three successive complexes which are relatively inert from electrochemical point of view. The results were in a good agreement with reported results in the literature.     

A study of ion exchange selectivity coefficient by cyclic voltammetric measurement

An equation to express ion exchange selectivity coefficient was derived and used for calculating that of PPY film with the results obtained by cyclic voltammetric measurement. PPY film was synthesized by electrochemical method in aqueous solution using K₄Fe(CN)₆ as supporting electrolyte, and the anions were doped into the film. Ion exchange behaviour of doped Fe (CN)₆^3-/4- in the PPY film with Cl^?, NO₃^? or F^? ions in solution has been studied, and the corresponding ion exchange selectivity coefficients were determined.     

Preconcentration procedures for trace cadmium determination in natural aqueous systems prior to zeeman etaas

Nanotrace Cd determination in natural waters using two new flotation collectors, lead(II) heptyldithiocarbamate, Pb(HpDTC)₂, and cobalt(III) heptyldithiocarbamate, Co(HpDTC)₃, are presented. The optimization of the most important experimental parameters for flotation is given. Zeeman electrothermal atomic absorption spectrometry (ZETAAS) is used as an instrumental technique for Cd measurement. The results are compared with those obtained by other preconcentration procedures as independent methods. The limit of detection of ZETAAS using Pb(HpDTC)₂ as collector is 4.8?ng/L, while using Co(HpDTC)₃ it is 3.0?ng/L.     

二茂铁衍生物LB膜修饰Pt电极的循环伏安法性能

本文研究了单取代二茂铁酯和双取代亚麻酸二茂铁酯LB膜修饰Pt电极的循环伏安法性能,用修饰电极的循环伏安模型对实验结果进行拟合,计算了在转移压力分别为20,30,40mN·m^-^1下LB膜修饰Pt电极的覆盖度,并分析和讨论了不同转移压力下修饰的二茂铁LB膜的电荷转移中介作用     

Structural characteristics and cyclic voltammetric behaviour of Sonogel-Carbon tyrosinase biosensors. A detailed comparative study of three immobilization matrixes

Structural characteristics an cyclic voltammetry of three amperommetric biosensors based on immobilization of tyrosinase on a Sonogel-Carbon electrode for detection of phenols are described. Cyclic voltammetry was applied to study the electrochemical behaviour of the electrode and the electrochemical reaction on the electrode surface. Scanning electron microscopy, X-ray energy dispersive spectroscopy and atomic force microscopy were used for the structure characterization of the electrode surface, enzyme film and polymers coatings. The influence of additive-protective polymers, such as polyethylene glycol and perfluorinated-Nafion ion-exchanger on the surface of the biosensor were explored.     

Adsorptive stripping square-wave voltammetric study of the degradation of lansoprazole in aqueous solutions

The adsorption and reduction behavior of lansoprazole has been studied by square-wave voltammetry at a hanging mercury drop electrode. A study of the variation in the reduction signal with solution variables, such as pH and concentration of lansoprazole, and instrumental variables, such as accumulation time and potential, frequency, pulse height and pulse amplitude, has resulted in optimization of the reduction signal for analytical purposes. The voltammetric procedure was successfully applied for rapid analysis of lansoprazole in stability studies without interference from the degradation products. It has also been used for the precise determination of lansoprazole in a pharmaceutical preparation.     

A study of polyamine complex formation with H+, Cu(II), Zn(II), Pb(II), and Mg(II) in aqueous solution

Summary The composition and stability of the following biogenic amine complexes have been investigated: 1,4-diaminobutane(Put), 4-azaoctane-1,8-diamine(Spd), 4,9-diazadodecan-1, 12-diamine(Spm) as well as homologues such as 1,3-diaminopropane(Put3), 4-azaheptane-1, 7-diamine(Spd3,3) and 4,8-diazaundecan-1,11-diamine(Spm3,3,3) with H⁺, Cu(II), Zn(II), Pb(II) and Mg(II). A potentiometric method was used. The VIS technique enabled the determination of coordination mode in copper/amine systems. It was found that Mg(II) does not form coordination compounds with any of the studied polyamines in solution. An increase in the concentration of ligand and metal was found to result in a stronger tendency towards the formation of protonated compounds accompanied by a decrease in the concentration of hydroxocomplexes. At physiologicalpH (7.4) an increase in the concentration of protonated compounds by approximately 15% was observed within the ligand concentration range from 0.001 mol dm^–3 to 0.0001 mol dm^–3 at a Cu(II) concentration of 0.000177 mol dm^–3.

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Untersuchungen zur Komplexbildung von Polyaminen mit H⁺, Cu(II), Zn(II), Pb(II) und Mg(II) in wäßriger Lösung

Zusammenfassung Anhand einer Analyse von potentiometrischen Daten wurden Zusammensetzung und Beständigkeit folgender biogener Aminkomplexe untersucht: 1,4-Diaminobutan(Put), 4-Azaoktan-1,8-diamin(Spd), 4,9-Diazadodekan-1,12-diamin(Spm), sowie auch deren Homologen 1,3-Diaminopropan(Put3), 4-Azaheptan-1,7-diamin(Spd3,3) und 4,8-Diazaundekan-1,11-diamin(Spm3,3,3) mit H⁺, Cu(II), Zn(II), Pb(II) und Mg(II). Mit Hilfe der VIS-Technik wurde die Koordinationsweise in Kupfer/Amin-Systemen bestimmt. Es wurde festgestellt, daß Mg(II) keine Koordinationsverbindungen mit den untersuchten Polyaminen bildet. Eine höhere Konzentration von Ligand und Metall führte zu stärkerer Tendenz der Bildung protonierter Verbindungen, wobei die Konzentration von Hydroxokomplexen kleiner wurde. Bei physiologischempH (7.4) wurde im Bereich der Ligand-Konzentration von 0.001 mol dm^–3 bis 0.0001 mol dm^–3 bei einer Cu(II)-Konzentration von 0.000177 mol dm^–3 ein Anstieg der Konzentration protonierter Verbindungen um etwa 15% beobachtet.

     

Exploiting flow injection and sequential injection anodic stripping voltammetric systems for simultaneous determination of some metals

Flow injection (FI) and sequential injection (SI) systems with anodic stripping voltammetric detection have been exploited for simultaneous determination of some metals. A pre-plated mercury film on a glassy carbon disc electrode was used as a working electrode in both systems. The same film can be repeatedly applied for at least 50 analysis cycles, thus reducing the mercury consumption and waste. A single line FI voltammetric system using an acetate buffer as a carrier and an electrolyte solution was employed. An injected standard/sample zone was mixed with the buffer in a mixing coil before entering a flow cell. Metal ions were deposited on the working electrode by applying a potential of −1.1 V vs Ag/AgCl reference electrode. The stripping was performed by anodically scanning potential of working electrode to +0.25 V, resulting a voltammogram. Effects of acetate buffer concentration, flow rate and sample volume were investigated. Under the selected condition, detection limits of 1 μg l⁻¹ for Cd(II), 18 μg l⁻¹ for Cu(II), 2 μg l⁻¹ for Pb(II) and 17 μg l⁻¹ for Zn(II) with precisions of 2–5% (n=11) were obtained. The SI voltammetric system was similar to the FI system and using an acetate buffer as a carrier solution. The SI system was operated by a PC via in-house written software and employing an autotitrator as a syringe pump. Standard/sample was aspirated and the zone was then sent to a flow cell for measurement. Detection limits for Cd(II), Cu(II), Pb(II) and Zn(II) were 6, 3, 10 and 470 μg l⁻¹, respectively. Applications to water samples were demonstrated. A homemade UV-digester was used for removing organic matters in the wastewater samples prior to analysis by the proposed voltammetric systems.     

Existence and reactivity of three forms of orthophthalaldehyde in aqueous solutions. Polarographic, voltammetric, and spectrophotometric study

Orthophthalaldehyde (1,2-dicarboxaldehyde) (OPA) forms in the presence of a strong nucleophile with amino acids isoindole derivatives. The reaction is used in fluorometric determination of amino acids. The mechanism of these processes is not understood. OPA is present in aqueous solutions in three forms: unhydrated (I(a)), monohydrated acyclic (I(b)), and cyclic hemiacetal (I(c)). The absence of data for the molar absorptivities of these forms, together with overlap of their absorption bands, limits the application of spectrophotometry. Measurement of polarographic limiting currents of forms I(a) and I(b) enables determination of equilibrium constants K1 (formation of I(b)) and K2 (for the ring formation). The presence of these forms was supported by 1H NMR and 13C NMR. The rate of hydration of OPA is general-acid-base-catalyzed, but that of dehydration shows only specific-acid-base catalysis. The rate of hydration is controlled by general-acid-base-catalyzed addition of water to I(a). The rate of dehydration depends on the opening of the ring in I(c), which is specific-acid-base-catalyzed. At pH > 10 OPA undergoes a complex set of acid-base reactions (Scheme 3). The presence of polarographic anodic waves and oxidation on the gold electrode indicates the importance of the presence of a geminal diol form (II(a)). Establishment of equilibria among the three forms of OPA together with reactions at pH > 10 has to be considered in elucidating the reaction scheme of procedures using OPA as a reagent in the determination of amino acids.     

Remediation of Cd2+ in aqueous systems by alkali-modified (Ca) biochar and quantitative analysis of its mechanism

Co-pyrolysis of straw and Ca(OH)₂ is a feasible modification method to improve the adsorption capacity of biochar for Cd. However, few studies have quantitatively analyzed the contribution of different adsorption mechanisms of alkali-modified biochar. In this study, the alkali-modified (Ca) biochar were prepared by co-pyrolyzing lime (Ca(OH)₂) and soybean straw (SBB) or rape straw (RSB) at 450 °C. The adsorption mechanism was investigated by a series of experiments and was provided by quantitative analysis. The maximum adsorption capacities of Cd²⁺ by Ca-SBB and Ca-RSB were calculated to be 78.49 mg g^?1 and 49.96 mg g^?1, which were 1.56 and 1.48 times higher than SBB (50.40 mg g^?1) and RSB (33.79 mg g^?1), respectively. Compared with the original biochar (SBB, RSB), alkali-modified biochar (Ca-SBB and Ca-RSB) were found to have faster adsorption kinetics and lower desorption efficiencies. The mechanism study indicated that Ca(OH)₂ modification effectively enhanced the contribution of ion exchange and decreased the contribution of functional groups complexation. After Ca(OH)₂ modification, precipitation and ion exchange mechanisms dominated Cd^2 + absorption on Ca-SBB, accounting for 49.85% and 34.94% of the total adsorption, respectively. Similarily ion exchange and precipitation were the main adsorption mechanism on Ca-RSB, accounting however for 61.91% and 18.47% of total adsorption, respectively. These results suggested that alkali-modified biochar has great potential to adsorp cadmium in wastewater.     

Study of redox behavior of Cd(II) and interaction of Cd(II) with proline in the aqueous medium using cyclic voltammetry

The redox behavior of Cd(II) and the interaction of Cd(II) with cyclic amino acid, proline, have been studied in 0.1 M KCl, 0.1 M NaClO₄ and acetate buffer of different pH. The CVs were recorded at glassy carbon electrode within the potential window 200 and ?1500 mV. The reference and counter electrode used were Ag/AgCl and Pt wire, respectively. The cyclic voltammograms show one pair of cathodic and anodic peaks for the Cd(II)/Cd(0) system indicating the involvement of two electron transfer processes. The peak potential shift and charge transfer rate constant (k_f) values strongly support the interaction between metal and ligand. The higher value of peak current ratio and peak potential separation (ΔE) indicate that the systems are quasireversible. The effect of supporting electrolyte and concentration of electro active species on the interaction were also studied.     

Photopolymerized silver-containing conducting polymer films. Part I. An electronic conductivity and cyclic voltammetric investigation

A photopolymerization process that simultaneously deposits electronically conducting polymer films and incorporates nanophase silver grains within the films, the silver grains having been formed in situ on irradiating cast, photopolymerizable formulations containing silver salts, was developed. Polymer films produced from formulations containing large organic anions were very flexible and strongly adherent to substrates. Polypyrrole films containing silver grains were characterized electronically on measuring their electronic conductivities and electrochemically on recording their cyclic voltammetric profiles. Conductivities were affected by the chemical identity and concentration of components added to photopolymerizable formulations. The best photopolymerized films had a conductivity of the order of 1 S cm⁻¹. Electronically conducting films derived from formulations consisting of a monomer, an electron acceptor/“dopant,” and a photoinitiator were electrochemically active. They possessed long-term stability under extended electrode potential cycling conditions, acceptable charge storage capacity, and the ability to oxidize or reduce redox couples in solution. Paper submitted for inclusion in the special issue of the Journal of Solid State Electrochemistry honouring the 85th birthday of Professor John O’M. Bockris.     

A conformation study of polyelectrolyte-dendritic surfactant complexes in dilute solutions

<正>Three dendronized polymers from generation one to generation three have been prepared by complexing negatively charged Frechet-type dendrons with a polyanion,poly(diallydimethylammonium chloride)(PDADMAC).The grafting degree has been confirmed mainly by elemental analysis.In dilute solutions of tetrahydrofuran,static light scattering studies indicate that the first generation complex has a coil-like conformation,even more flexible than PDADMAC.The second and third generation complexes exhibit polyelectrolyte behavior.Dynamic light scattering experiments indicate that all the three complexes have almost the same hydrodynamic radius,indicating that they might own similar coil conformation.Atomic force microscopy shows the existence of disordered globules formed by one or a couple of complex coils.All these observations can be explained by the flowerlike coil conformation,which is formed by the intra-molecular association.This is totally different from the stretched chain conformation formed by covalently connected dendronized polymers.This result also explains why some ordered supramolecular structures,found in condensed state of the similar complexes,are not as perfect as those of conventional dendronized polymers.