聚1,8-萘二胺修饰玻碳电极测定痕量汞

采用电化学聚合的方法制备了聚1,8-萘二胺修饰玻碳电极,建立了吸附富集-阳极溶出伏安法测定痕量Hg2+的新方法.优化了各种实验参数(如富集底液的pH,富集时间等),并考察了其它离子的干扰.在最佳实验条件下,Hg2+在0.001～0.1 mg/L及0.1～5.0 mg/L质量浓度范围内均与溶出峰电流成良好的线性关系,检出限为0.0005 mg/L.该法可用于实际工业废水中汞的测定.     

Electrode Modified with Langmuir–Blodgett (LB) Film of Calixarenes for Preconcentration and Stripping Analysis of Hg(II)

A new type of current sensor, Langmuir–Blodgett (LB) film of calixarene on the surface of glassy carbon electrode (GCE) was prepared for determination of mercury by anodic stripping voltammetry (ASV). An anodic stripping peak was obtained at 0.15 V (vs. SCE) by scanning the potential from ?0.6 to +0.6 V. Compared with a bare GCE, the LB film coated electrode greatly improves the sensitivity of measuring mercury ion. The fabricated electrode in a 0.1 M H₂SO₄+0.01 M HCl solution shows a linear voltammetric response in the range of 0.07–40 μg L^?1 and detection limit of 0.04 μg L^?1 (ca. 2×10^?10 M). The high sensitivity, selectivity, and stability of this LB film modified electrode demonstrates its practical application for a simple, rapid and economical determination of Hg²⁺ in a water sample.     

Polyviologen Modified Glassy Carbon Electrode Employed for Anodic Stripping Voltammetric Determination of Mercury(II)

In this study, a polyviologen modified glassy carbon electrode (PVGCE) was used to detect Hg(II) in aqueous solutions containing significant amounts of chloride anions in order to demonstrate the electroanalytical application of the electropolymerized polyviologen. The polyviologen thin film was formed on the electrode surface by applying a constant potential of ?1.0 V in the pH 4.2 Britton–Robinson (BR) buffer solution that contains 0.1 wt% of viologen oligomers. The PVGCE was found capability to improve the detection limit of Hg(II) in the solutions with high concentration of chloride because Hg(II) forms negative complex ions HgCl that can be accumulated to PVGCE by the anion‐exchange characteristic of polyviologen. With 5 minutes accumulation at ?0.2 V, the adsorbed HgCl anions were reduced to Hg and deposited on the electrode surface, and were determined with the following anodic stripping differential pulse voltammetry (ASDPV). The dependence of anodic stripping current versus concentration was linear from 1 ppb (5 nM) to 100 ppb (0.5 μM) with a regression coefficient of 0.9959.     

High electrochemiluminescence intensity of the Ru(bpy)3 2+/oxalate system on a platinum net electrode

A new method for enhancing the electrochemiluminescence (ECL) intensity of the Ru(bpy)₃ ²⁺/ oxalate system is presented. When a platinum net was used as a working electrode and a platinum foil as an auxiliary electrode, the ECL intensity of the system was enhanced greatly. In addition, a cathodic peak appeared at 0.18 V (vs. SCE) on a platinum net electrode, and ECL of the system was observed at 0.18 V.     

Langmuir-Blodgett film of p-tert-butylthiacalix[4]arene modified glassy carbon electrode as voltammetric sensor for the determination of Hg(II)

The π-A isotherms and UV-vis spectra of the transferred films suggested that the monolayer of p-tert-butylthiacalix[4]arene can coordinate with Hg²⁺ at the air-water surface. From these observations, a glassy carbon electrode coated with Langmuir-Blodgett film of p-tert-butylthiacalix[4] arene as a new voltammetric sensor is designed for the determination of trace amounts of Hg²⁺. Compared with bare glassy carbon electrode and modified glassy carbon electrode using direct coating method, the Langmuir-Blodgett film-modified electrode can greatly improve the measuring sensitivity of Hg²⁺. Under the selected conditions, the Langmuir-Blodgett film-modified electrode in 0.1 mol L⁻¹ H₂SO₄ + 0.01 mol L⁻¹ KCl solution shows a linear voltammetric response for Hg²⁺ in the range of 5.0 × 10⁻¹⁰ to 1.5 × 10⁻⁷ mol L⁻¹, with a detection limit of 2.0 × 10⁻¹⁰ mol L⁻¹. The proposed method was also applied to determine Hg²⁺ in water samples (tap, lake and river water). In addition, the fabricated electrode exhibited a distinct advantage of simple preparation, non-toxicity, good reproducibility and good stability.     

Silver(I) ions-enhanced electrochemiluminescence of tris(2,2-bipyridyl)ruthenium(II)

In this paper, we demonstrate an electrochemiluminescence (ECL) enhancement of tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) by the addition of silver(I) ions. The maximum enhancement factor of about 5 was obtained on a glassy carbon electrode in the absence of co-reactant. The enhancement of ECL intensity was possibly attributed to the unique catalytic activity of Ag⁺ for reactions between Ru(bpy)₃³⁺ with OH. The higher enhancement was observed in phosphate buffer solutions compared with that from borate buffer solutions. This resulted from the fact that formation of nanoparticles with large surface area in the phosphate buffer solution exhibited high catalytic activity. The amount of Ag⁺, solution pH and working electrode materials played important roles for the ECL enhancement. We also studied the effects of Ag⁺ on Ru(bpy)₃²⁺/tripropylamine and Ru(bpy)₃²⁺/C₂O₄²⁻ ECL systems.     

Functionalized calix[4]arene as an ionophore: Synthesis,crystal structures and complexation study with Na and K ions

Calix[4]arenes with substituents at three of the four OH groups of the lower rim have been synthesized to investigate their properties as ionophores for Na⁺ and K⁺ metal ions. Crystal structures of these trisubstituted compounds revealed that the calixarene moiety has adopted a partial cone conformation, however the precise shape of the molecule, and intra- and intermolecular interactions, are significantly different due to variations of the substituents. Compound L² encapsulated an acetonitrile molecule in the cavity of the calix moiety, held by C–H?π interactions. In the case of L³, the 2-(2-chloroethoxy)-ethanol substituent is involved in strong intramolecular C–H?π interactions with the centroid of the phenyl rings of the calix, bringing the 2-(2-chloroethoxy)-ethanol moiety inward the calix cone, which prevented the entry of any solvent molecule into the cavity. The complexation properties of L²–L⁴ with Na⁺ and K⁺ ions have been investigated in chloroform–methanol mixture by ¹H NMR and an attempt has been made to isolate these complexes in the solid state. Complexation studies reveal that only L³ forms a complex selectively with K⁺, involving 2-(2-chloroethoxy)-ethanol as a coordinating moiety. The association constant (1.4 × 10⁵ M⁻¹) of the complex has also been determined.     

Recombination of KrD and XeD ions with electrons

Recombination rate coefficients of protonated and deuterated ions KrH⁺, KrD⁺, XeH⁺ and XeD⁺ were measured using Flowing Afterglow with Langmuir Probe (FALP). Helium at 1600 Pa and at temperature 250 K was used as a buffer gas in the experiments. Kr, Xe, H₂ and D₂ were introduced to a flow tube to form the desired ions. Because of small differences in proton affinities of Kr, D₂ and H₂ mixtures of ions, KrD⁺/D₃⁺ and KrH⁺/H₃⁺ are formed in the afterglow plasma, influencing the plasma decay. To obtain a recombination rate coefficient for a particular ion, the dependencies on partial pressures of gases used in the ion formation were measured. The obtained rate coefficients, α_KrD+(250 K) = (0.9 ± 0.3) × 10⁻⁸ cm³ s⁻¹ and α_XeD+(250 K) = (8 ± 2) × 10⁻⁸ cm³ s⁻¹ are compared with α_KrH+(250 K) = (2.0 ± 0.6) × 10⁻⁸ cm³ s⁻¹ and α_XeH+(250 K) = (8 ± 2) × 10⁻⁸ cm³ s⁻¹.     

Application of artificial neural network to simultaneous potentiometric determination of silver(I), mercury(II) and copper(II) ions by an unmodified carbon paste electrode

The response characteristics and selectivity coefficients of an unmodified carbon paste electrode (CPEs) towards Ag⁺, Cu²⁺ and Hg²⁺ were evaluated. The electrode was used as an indicator electrode for the simultaneous determination of the three metal ions in their mixtures via potentiometric titration with a standard thiocyanate solution. A three-layered feed-forward artificial neural network (ANN) trained by back-propagation learning algorithm was used to model the complex non-linear relationship between the concentration of silver, copper and mercury in their different mixtures and the potential of solution at different volumes of the added titrant. The network architecture and parameters were optimized to give low prediction errors. The optimized networks were able to precisely predict the concentrations of the three cations in synthetic mixtures.     

Electroanalytical Determination of Cadmium(II) and Lead(II) Using an Antimony Nanoparticle Modified Boron‐Doped Diamond Electrode

We report the simultaneous electroanalytical determination of Pb²⁺ and Cd²⁺ by linear sweep anodic stripping voltammetry (LSASV) using an antimony nanoparticle modified boron doped diamond (Sb‐BDD) electrode. Sb deposition was performed in situ with the analytes, from a solution of 1 mg L^?1 SbCl₃ in 0.1 M HCl (pH 1). Pb²⁺ inhibited the detection of Cd²⁺ during simultaneous additions at the bare BDD electrode, whereas in the presence of antimony, both peaks were readily discernable and quantifiable over the linear range 50–500 μg L^?1.     

Silver(I)-selective electrode based on [Bz2Oxo4(18)dieneS4] tetrathia macrocyclic carrier

A polystyrene-based membrane of 7,8:16,17-dibenzo-6,9,15,18-tetraoxo-1,5,10,14-tetrathiacyclooctadeca-7,16-diene [Bz₂Oxo₄(18)dieneS₄] was fabricated using sodium tetraphenylborate (NaTPB) and dioctyl phthalate (DOP) as anion excluder and plasticizing agent. The best performance was obtained from the membrane with the composition ionophore [Bz₂Oxo₄(18)dieneS₄]:polystyrene:DOP:NaTPB, 5:100:150:10 (w/w). The response of the electrode was linear over a wide range of concentration, 1.26×10^–6–1.00×10^–1 mol L⁻¹ for silver ion with a Nernstian slope of 58.4±0.1 mV per decade and a detection limit of 1.0×10⁻⁶ mol L⁻¹. The electrode was found to be chemically inert and of adequate stability with a response time of 10 s and could be used for a period of 3 months without change of potential. It worked satisfactorily in mixtures containing up to 35% (v/v) non-aqueous content. The proposed membrane sensor had good selectivity for Ag⁺ over a wide variety of metal ions in the pH range 2.2–8.5. It was successfully used as an indicator electrode in potentiometric titration of silver ion. The electrode was also useful for determination of Ag⁺ in waste from photographic films.     

Electrochemiluminescence Enhancement of CdTe Quantum Dots by the Addition of Silver(I) Ions

Water-soluble CdTe quantum dots (QDs) were synthesized by using a 3-mercaptopropionic acid (MPA) capped method. Stable electrochemiluminescence (ECL) was obtained when the CdTe QDs were immobilized onto a glassy carbon electrode (GCE) by Layer-By-Layer (LBL) assembly of CdTe QDs and polydiallyldimethylam-monium chloride (PDDA) by using 2-(dibutylamino)-ethanol (DBAE) as a co-reactant. The ECL enhancement of CdTe QDs by the addition of silver(I) ions was also investigated. The maximum enhancement factor about 4 was obtained on a GCE in the presence and absence of the co-reactant. The enhancement was observed in phosphate-citric acid and phosphate buffer solutions (PBS), but not in borate buffer solution (BBS). This was newly formed Ag nanoparticles or silver(I) complex with large surface area and high catalytic activity in the phosphate-citric acid and phosphate buffer solutions, thus resulting in ECL enhancement.     

Time-dependent Cu-induced gelation of poly(ethylene-alt-maleic acid) in aqueous solution

The complexation of Cu²⁺ ions with an alternating copolymer of maleic acid (MAc) and ethylene in aqueous solution was followed through turbidimetry and absorption spectrophotometry as a function of the polymer concentration and the metal ion-to-polymer molar ratio, r. The introduction of Cu²⁺ ions was performed in aqueous solution through neutralization of the polyacid with Cu(OH)₂ powder. A gelation window between homogeneous and phase-separated solutions was observed in the phase diagram of the polymer/Cu²⁺ mixture and the viscoelastic properties of the hydrogels were evaluated through rheology measurements. It is found that the stiffness of the hydrogels can be tuned by the polymer concentration and the mixing ratio r. Moreover, the stiffness of the hydrogels increases substantially with time. In fact, this time evolution may be as long as one month or longer if the composition of the aqueous solution is close to the gelation threshold. The gelation properties can be qualitatively explained from the possible formation of binuclear polymer/Cu²⁺ complexes in aqueous solutions, as indicated from the absorption spectroscopy results.     

Determination of anionic surfactants by bis(ethylenediamine)copper(II) extraction and anodic stripping voltammetry

A stripping voltammetric finish for the measurement of total anionic surfactant has been developed. A limit of detection of 5.0 μg 1^?1 anionic surfactant was observed with a linear calibration from 5.0 to 500 μg 1^?1 in the original sample.     

New approach for synthesis of poly(ethylglyoxylate) using Maghnite-H+, an Algerian proton exchanged montmorillonite clay,as an eco-catalyst

In this works, we have explored a new method for a green synthesis of poly(ethylglyoxylate) (PEtG). This method consists on using a montmorillonite clay called “Maghnite-H⁺” as an eco-catalyst to replace triethylamine which is toxic. Cationic polymerization experiments are performed in bulk conditions at three temperatures (?40°C, 25°C, 80°C) and in THF solutions at room temperature (25°C). At 25°C, an optimum ratio of 5 wt% of catalyst leads to molar masses up to 22000 g/mol in THF solutions. Polymerizations in bulk conditions lead to slightly lower masses than experiments conducted in THF solutions. However, bulk polymerization of ethyleglyoxylate remains a preferable method in order to avoid the use of a solvent and therefore to stay in the context of green chemistry. The structure of obtained polymers are characterized and confirmed by ¹H and ¹³C NMR. Thermogravimetric Analysis (TGA) shows an enhanced thermal stability for end-capped PEtG compared to non-terminated PEtG. The best conversion rate (92%) is observed in bulk conditions at 25°C for a reaction time of 48h. An activation energy could be calculated from bulk experiments (Ea = 6.9 kJ/mol). An interesting advantage of Maghnite-H⁺ is an easy recoverage by a simple filtration from the polymer solution.     

Simultaneous voltammetric measurement of ascorbic acid and dopamine on poly(caffeic acid)-modified glassy carbon electrode

A poly(caffeic acid) thin film was deposited on the surface of a glassy carbon electrode by potentiostatic technique in an aqueous solution containing caffeic acid. The poly(caffeic acid)-modified electrode was used for the determination of ascorbic acid (AA), dopamine (DA), and their mixture by cyclic voltammetry. This modified electrode exhibited a potent and persistent electron-mediating behavior followed by well-separated oxidation peaks toward AA and DA at a scan rate of 10 mV s⁻¹ with a potential difference of 135 mV, which was large enough to determine AA and DA individually and simultaneously. The catalytic peak current obtained was linearly dependent on the AA and DA concentrations in the range of 2.0 × 10⁻⁵−1.2 × 10⁻³ and 1.0 × 10⁻⁶−4.0 × 10⁻⁵ mol L⁻¹ in 0.15 mol L⁻¹ phosphate buffer (pH 6.64). The detection limits for AA and DA were 9.0 × 10⁻⁶ and 4.0 × 10⁻⁷ mol L⁻¹, respectively. The modified electrode shows good sensitivity, selectivity, and stability and has been applied to the determination of DA and AA in real samples with satisfactory results.     

A.c. impedance behaviour of processes involving adsorption and reactivity of guanidonium-type cations at Pt(1 0 0) surface

The present paper reports a.c. impedance spectroscopic studies on adsorption of guanidonium (G⁺) and N,N-dimethylguanidonium (DMG⁺) resonant cations at Pt(1 0 0) single-crystal surface. The resulted information provided confirmation of the role of electrosorption of the above-mentioned molecule–ions through evaluation of the associated charge-transfer resistances and capacitances for the Pt(1 0 0) plane in 0.5 M H₂SO₄. These results also provided support for the interfacial ion-pairing mechanism that had been based on the voltammetric and in situ FTIR spectroscopic results published earlier.     

Development of a Sensor Based on Poly(1,2-diaminoanthraquinone) for Individual and Simultaneous Determination of Mercury (II) and Bismuth (III)

Contamination of natural water by mercury (Hg²⁺) and bismuth (Bi³⁺) metal ions have been extensively studied due to their toxic effects. A validated square-wave anodic stripping voltammetry (SW-ASV) method for determining Bi³⁺ and Hg²⁺ ions individually and simultaneously is described. A new electrochemical sensor was constructed using a gold (Au) electrode that has been modified with poly(1,2-diaminoanthraquinone) (p-1,2-DAAQ). Scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy were used to characterize the p-1,2-DAAQ/Au modified electrode. Factors such as the polymer film thickness, electrolyte, square wave parameters and preconcentration conditions were optimized to improve the performance of the modified Au electrode. Good linear responses were achieved in the concentration ranges of 1–200 μg L⁻¹ and 1–50 μg L⁻¹ forBi³⁺ and Hg²⁺, respectively, and the limits of detection were 0.27 μg L⁻¹ (Bi³⁺) and 0.29 μg L⁻¹ (Hg²⁺). The interference study results illustrated the high selectivity of the modified electrode for detection of Bi³⁺ and Hg²⁺. The proposed SW-ASV method was successfully applied for Bi³⁺ and Hg²⁺analyses in different real water samples.     

聚次甲基蓝修饰玻碳电极测定叶酸

利用循环伏安法将次甲基蓝修饰到玻碳电极表面,制备了聚次甲蓝修饰电极(PMB/GCE),并研究了此电极的化学性质及对叶酸的电化学响应特性.在磷酸盐缓冲液中PMB/GCE电极对叶酸有良好的催化作用并出现一个灵敏的还原峰,用循环伏安法测得峰电流与叶酸的浓度在0.1×10-3～2.9×10 -3 mol/L范围内呈良好线性关系...     

Square-wave voltammetric stripping analysis of thallium(III) at a poly(4-vinylpyridine)/mercury film electrode

A poly(4-vinylpyridine)/mercury film electrode (PVP/MFE) was used for the determination of trace thallium(III) by square-wave anodic stripping voltammetry (SWASV). Thallium(III) is preconcentrated onto the PVP/MFE as the anionic forms in chloride medium by the ion-exchange effect of the PVP. The high solubility of thallium in mercury further facilitates the accumulation effect. Various factors influencing the determination of thallium(III) were thoroughly investigated. This modified electrode displayed good resistance to interferences from surface-active compounds and common ions and increased sensitivity when used in conjunction with SWASV. In addition, detection can be achieved without deoxygenation and the electrode can be easily renewed. Applicability to various water samples is illustrated.