Enhanced solid-state electrogenerated chemiluminescence of Au/CdS nanocomposite and its sensing to H2O2

Au nanoparticles (AuNPs) are good quenchers once they closely contact with luminophore. Here we reported a simple approach to obtain enhanced electrogenerated chemiluminescence (ECL) behavior based on Au/CdS nanocomposite films by adjusting the amount of AuNPs in the nanocomposite. The maximum enhancement factor of about 4 was obtained at an indium tin oxide (ITO) electrode in the presence of co-reactant H₂O₂. The mechanism of this enhancement was discussed in detail. The strong ECL emission from Au/CdS nanocomposites film was exploited to determine H₂O₂. The resulting ECL biosensors showed a linear response to the concentration of H₂O₂ ranging from 1.0 × 10⁻⁸ to 6.6 × 10⁻⁴ mol L⁻¹ with a detection limit of 5 nmol L⁻¹ (S/N = 3) and good stability and reproducibility.     

Electrogenerated chemiluminescent behavior of MCLA at an indium-tin-oxide electrode

In this paper, the electrogenerated chemiluminescence (ECL) behavior of 6-(4-methoxyphenyl)-2-methylimidazo[1,2-a]pyrazin-3(7H)-one (MCLA) at an indium-tin-oxide (ITO) electrode in phosphate buffer solution has been investigated when linear sweep voltammetry was applied. The optimum chemical conditions and electrochemical parameters for this ECL system have been investigated in detail. Under the optimum conditions, it was found that the ECL intensity was linear with the concentration of MCLA in the range of 6.0 × 10⁻⁷ to 1.0 × 10⁻⁵ mol/L, and its detection limit for MCLA was 2.0 × 10⁻⁷ mol/L. The possible mechanism for ECL of MCLA at the ITO electrode was also discussion. Furthermore, it was found that some sophora flavescens, such as matrine and oxymatrine, might enhance the ECL intensity of MCLA. Therefore, it is possible to develop a new ECL method for determination of matrine and oxymatrine.     

Ru(bpy)3-doped silica nanoparticle DNA probe for the electrogenerated chemiluminescence detection of DNA hybridization

A sensitive electrogenerated chemiluminescence (ECL) detection of DNA hybridization, based on tris(2,2′-bipyridyl)ruthenium(II)-doped silica nanoparticles (Ru(bpy)₃²⁺-doped SNPs) as DNA tags, is described. In this protocol, Ru(bpy)₃²⁺-doped SNPs was used for DNA labeling with trimethoxysilylpropydiethylenetriamine(DETA) and glutaraldehyde as linking agents. The Ru(bpy)₃²⁺-doped SNPs labeled DNA probe was hybridized with target DNA immobilized on the surface of polypyrrole (PPy) modified Pt electrode. The hybridization events were evaluated by ECL measurements and only the complementary sequence could form a double-stranded DNA (dsDNA) with DNA probe and give strong ECL signals. A three-base mismatch sequence and a non-complementary sequence had almost negligible responses. Due to the large number of Ru(bpy)₃²⁺ molecules inside SNPs, the assay allows detection at levels as low as 1.0 × 10⁻¹³ mol l⁻¹ of the target DNA. The intensity of ECL was linearly related to the concentration of the complementary sequence in the range of 2.0 × 10⁻¹³ to 2.0 × 10⁻⁹ mol l⁻¹.     

On the adsorption of hexaammineruthenium (III) at anionic self-assembled monolayers

The binding of the electroactive hexaammineruthenium (III) complex ions to anionic self-assembled monolayers (SAMs) has been investigated by means of chronocoulometry and ac voltammetry. From chronocoulometric data recorded in 10⁻² M LiClO₄ containing different [Ru(NH₃)₆]³⁺ concentrations, we have established the adsorption isotherm of [Ru(NH₃)₆]³⁺ on a compact monolayer of 2-mercaptobenzimidazole-5-sulfonate (MBIS) self-assembled on Au(1 1 1). The data were satisfactorily fitted to the linearized Langmuir adsorption isotherm and a binding constant of 4.0 (±0.4) × 10⁶ M⁻¹ has been determined.The electrostatic binding of [Ru(NH₃)₆]³⁺ to a dilute PNA-DNA monolayer formed after hybridization on a PNA-modified gold electrode by self-assembly from a mixed solution of mercaptobutan-1-ol and PNA oligonucleotides has been studied by ac voltammetry. The admittance of the PNA-modified electrode after hybridization with complementary DNA was measured in 0.01 M Tris-HCl buffer containing different [Ru(NH₃)₆]³⁺ concentrations. Based on these data, a binding constant of [Ru(NH₃)₆]³⁺ to the surface-confined PNA-DNA duplex was derived from the Langmuir isotherm and amounts to 2.9 (±0.3) × 10⁵ M⁻¹. As the interactions between [Ru(NH₃)₆]³⁺ and the immobilized PNA-DNA hybrids on the gold surface are essentially electrostatic, the adsorption of the highly charged cationic redox complex at low concentrations to the negatively charged PNA-DNA modified surface is in large competition with other monovalent cations present in the electrolyte at higher concentrations. The influence of competing sodium cations was thus studied by adding different NaCl concentrations in the 0.01 M Tris-HCl electrolyte.     

Influence of metal coordination on conductivity behavior in poly(butadiene-acrylonitrile)-CoCl2 system

The metal complex formation and the electrical properties of amorphous solid polymer electrolytes, based on poly(butadiene-acrylonitrile) copolymer (PBAN) and CoCl₂, have been studied over the homogeneity region of the system limited by the CoCl₂ concentration of 1.89 mol kg⁻¹. It has been found that ionic conductivity is carried out by the unipolar anion transfer at lower CoCl₂ concentrations (up to 0.10 mol kg⁻¹). As the CoCl₂ concentration increases, electronic conductivity appears in addition to ionic conductivity, and the former becomes dominant, starting from 0.38 mol kg⁻¹. It has been shown that the nature of charge carriers is determined by the composition of metal complexes formed by CoCl₂ and the macromolecular solvent PBAN. At lower concentrations, the [Co₂L₂Cl₄]⁰ dimers are the predominant species (L being macromolecule side groups CN), and their dissociation is followed by the formation of mobile Cl⁻ anions and immobile binuclear [Co₂Cl₃]⁺ complexes. As CoCl₂ concentration increases, polynuclear [Co_nL₂Cl_2n]⁰ (n > 2) complexes appear (L being CN and CC groups of PBAN). Specific features of chemical bonds in π-complexes of transition metals result in the appearance of electronic charge carriers. The abrupt increase in conductivity observed at the highest CoCl₂ concentration is connected with the formation of a percolation network of polynuclear [Co_nL₂Cl_2n]⁰ complexes.     

Variations in the crystalline deposits formed upon electrochemical oxidation of the anions, [Ir(CO)2X2] (X = Cl, Br, and I)

The electrochemical properties of the ions [Ir(CO)₂X₂]⁻ (X = Cl, Br, and I) have been studied in dichloromethane solutions using cyclic voltammetry, chronoamperometry, electrochemical quartz crystal microbalance (EQCM), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and infrared spectroscopy. For the chloro and bromo salts, the anion [Ir(CO)₂X₂]⁻ is oxidized initially to form [Ir(CO)₂X₂]⁺. The standard rate constants for the two-electron oxidations of [Ir(CO)₂X₂]⁻ are 7.8(±0.6) × 10⁻³ and 9.2(±0.9) × 10⁻⁴ cm s⁻¹ for the redox couples, [Ir(CO)₂Cl₂]^−/+ and [Ir(CO)₂Br₂]^−/+, respectively. The processes following electrolysis lead to the formation of two types of crystalline deposits on the electrode surface: needles and plates. The relative amounts of these solid phases that form depend mainly on the concentration of iridium complex in solution and on the time window of experiment. The strong intermetallic Ir-Ir interaction is responsible for the formation of the one-dimensional iridium complex chain. The crystal structures of the needle phases formed from [Ir(CO)₂Cl₂]⁻ and [Ir(CO)₂Br₂]⁻ are the same and belong to the space group Cmcm (no. 63). The stoichiometry of the one-dimensional crystals depends on the constitution of the supporting electrolyte: (TAA)_0.6[Ir(CO)₂Cl₂] and (TAA)_0.7[Ir(CO)₂Br₂] (TAA is tetra(alkyl)ammonium cation) salts are formed on the electrode surface. The formation of large three-dimensional crystal is responsible for the accumulation of electroactive materials on the electrode surface. The irreversible oxidation of [Ir(CO)₂I₂]⁻ leads only to the formation of large, plate-like crystals on the electrode surface, no needles are formed.     

Hydroxyl radical-related electrogenerated chemiluminescence reaction for a ruthenium tris(2,2′)bipyridyl/co-reactants system at boron-doped diamond electrodes

An electrogenerated chemiluminescence (ECL) reaction of the Ru(bpy)₃²⁺ (2,2′-bipyridyl, bpy)/co-reactant system in the extremely high-potential region (over 2.6 V versus Ag/AgCl) was probed using a boron-doped diamond (BDD) electrode. At the BDD electrode, three ECL waves (1.25, 2.30 and 3.72 V) were observed in cyclic voltammograms for 20 mM ascorbic acid (AA). For the ECL peaks observed at 1.25 V corresponding to the oxidation potential for Ru(bpy)₃²⁺ (1.15 V), the light intensities and current densities were found to depend on the square root of the AA concentration. This suggests that AA oxidation, followed by the formation of the reducing radical that is necessary for generating the excited state of Ru(bpy)₃^2+* occurred through homogeneous electron-transfer between Ru(bpy)₃³⁺ and the AA species. However, for the ECL peaks at 2.30 V, the current densities and light intensities linearly increased with increasing AA concentration, suggesting that the reducing radical was formed through the direct oxidation at the electrode surface. The ECL reaction at 3.72 V was observed only at the BDD electrode and not at other electrodes. The onset potentials for the light intensity were approximately 2.6 V, independently of the type of the co-reactants (e.g. 2-propanol and AA). The peak potentials exhibited linear relation with the co-reactant concentration. In the analysis of the ECL intensity for various co-reactants (alcohols) that show different reactivity for the hydrogen abstraction reaction, the order of the light intensities at the peaks for alcohols was found to be consistent with that for the rate constants of the hydrogen abstraction reaction. These results indicate that the co-reactant radical was formed through the hydrogen abstraction reaction with the hydroxyl radical (HO) generated during the oxygen evolution reaction.     

Electrochemiluminescent determination of nicotine based on tri(2,2′-bipyridyl) ruthenium (II) complex through flow injection analysis

This paper describes the electrogenerated chemiluminescence (ECL) processes of Ru(bpy)₃²⁺/nicotine system at ITO working electrode. An ECL-based method for rapid and sensitive detection of nicotine in phosphate buffer solution at pH 8.0 is established. Strong ECL emission was observed at a positive potential of 1.4 V vs. Ag/AgCl. A possible ECL mechanism is proposed for the Ru(bpy)₃²⁺/nicotine system, the oxidation product of nicotine at the electrode surface reacts with the 3+ state of ruthenium bipyridyl (2+) complex and form ruthenium complex exited state ions and thus releases photons. Effect of pH (medium/electrolyte), working potential, buffer composition, buffer concentration, reactant and co-reactant (nicotine) concentration, flow rate and loop size on the ECL spectrum of the Ru(bpy)₃²⁺/nicotine were studied. At the optimized experimental conditions, lower detection limit for nicotine was observed as 1.2 nmol L⁻¹ (S/N = 3). Linear relationship between ECL current and concentration of nicotine was observed (up to 100 μmol L⁻¹) with R-value of 0.997. The relative standard deviation with 5 μmol L⁻¹ concentration of nicotine for 20 analyses was only 1.4%. A 94% recovery rate was observed in a real sample analysis without any complications/disturbance in measurement. Interferences of humid acid, camphor and SDS were not observed in their presence in the sample solution. The established procedure for nicotine quantification manifests fascinating results and can be suggested for further applications.     

Electrochemiluminescent behavior of luminol on the glassy carbon electrode modified with CoTPP/MWNT composite film

A glassy carbon electrode (GCE) modified with cobalt(II) meso-tetraphenylporphrine/multiwall-carbon nanotube (CoTPP/MWNT) was applied to investigate the electrochemiluminescent (ECL) behavior of luminol. The ECL intensity of luminol was found to be increased greatly on this modified electrode. The presence of cobalt(II) meso-tetraphenylporphrine (CoTPP) can catalyze the reduction of oxygen on the electrode surface to produce HOO⁻, which can increase the ECL intensity of luminol. Moreover, MWNT can provide the more effective area of the electrode, and can act as a promoter to enhance the electrochemical reaction. The proposed method enables a detection limit for luminol of 1.0 × 10⁻⁸ mol/L in the neutral solution. Under the optimum condition, the enhanced ECL intensity of luminol by H₂O₂ had a linear relationship with the concentration of H₂O₂ in the range of 1.0 × 10⁻⁷ to 8.0 × 10⁻⁸ mol/L with the detection limit of 5.0 × 10⁻⁹ mol/L.     

An electrochemiluminescent biosensor for vitamin C based on inhibition of luminol electrochemiluminescence on graphite/poly(methylmethacrylate) composite electrode

A novel graphite/poly(methyl methacrylate) (graphite/PMMA) electrode was prepared in this paper. It was found that the developed polymer graphite paste electrode has some advantages in electrochemistry and electrochemiluminescence (ECL), such as high sensitivity, good reproducibility, quick and wide linear range of response to some biomolecules. The ECL behavior of luminol has been investigated in detail at the graphite/PMMA electrode, and vitamin C was found to be able to inhibit this ECL system. Based on which an inhibited ECL detection method has been developed for determination of vitamin C in this paper. The proposed method exhibited good reproducibility, wide-range linearity, high sensitivity and stability with a detection limit of 8.3 × 10⁻⁹ mol L⁻¹ (signal-to-noise ratio = 3) and linear response range of 2.5 × 10⁻⁸-1.0 × 10⁻⁴ mol L⁻¹. The relative standard deviation was 2.3% for 5 × 10⁻⁶ mol L⁻¹ vitamin C (n = 9). The possible mechanism for inhibition of luminol on graphite/PMMA electrode has also been proposed.     

Preparation, structure and electrochemistry of a polypyrrole hybrid film with [Pd(dmit)2], bis(1,3-dithiole-2-thione-4,5-dithiolate)palladate(II)

The synthesis of a hybrid material obtained by electropolymerization of a solution of pyrrole and [NEt₄]₂[Pd(dmit)₂] (1,3-dithiole-2-thione-4,5-dithiolate, [dmit]²⁻, [C₃S₅]²⁻) in acetonitrile solution is reported. FTIR and UV-vis spectroscopy showed that the [Pd(dmit)₂]²⁻ anion had been inserted in the polypyrrole framework without modification during the electropolymerization process. Cyclic voltammetry showed that the material has electroactivity undergoing redox processes related to the conducting polymer and the counteranion. The electrochemical results also suggest that the counteranion is not trapped in the PPy matrix undergoing anion exchange during the redox cycle of PPy. The PPy/[Pd(dmit)₂]²⁻ exhibits good thermal stability and has a higher intrinsic conductivity value (4.27 × 10⁻³ S cm⁻¹) than do other PPy/dmit films previously studied.     

Poly(o-aminophenol) film prepared in the presence of sodium dodecyl sulfate: Application for nickel ion dispersion and the electrocatalytic oxidation of methanol and ethylene glycol

Poly(o-aminophenol) (POAP) was formed by successive cyclic voltammetry in monomer solution in the presence of sodium dodecyl sulfate (SDS) on the surface of a carbon paste electrode. The electrochemical behavior of the SDS-POAP carbon paste electrode has been investigated by cyclic voltammetry in 0.5 M HClO₄ and 5 mM K₄[Fe(CN)₆]/0.1 M KCl solutions as the supporting electrolyte and model system, respectively. Ni(II) ions were incorporated into the electrode by immersion of the polymeric modified electrode having amine groups in 0.1 M Ni(II) ion solution. Cyclic voltammetric and chronoamperometric experiments were used for the electrochemical study of this modified electrode. A good redox behavior of the Ni(III)/Ni(II) couple at the surface of electrode can be observed. The electrocatalytic oxidations of methanol and ethylene glycol (EG) at the surface of the Ni/SDS-POAP electrode were studied in a 0.1 M NaOH solution. Compared to bare carbon paste and POAP-modified carbon paste electrodes, the SDS-POAP electrode significantly enhanced the catalytic efficiency of Ni ions for methanol oxidation. Finally, using a chronoamperometric method, the catalytic rate constants (k) for methanol and ethylene glycol were found to be 2.04 × 10⁵ and 1.05 × 10⁷ cm³ mol⁻¹ s⁻¹, respectively.     

On the performances of lead dioxide and boron-doped diamond electrodes in the anodic oxidation of simulated wastewater containing the Reactive Orange 16 dye

The performances of the Ti-Pt/β-PbO₂ and boron-doped diamond (BDD) electrodes in the electrooxidation of simulated wastewaters containing 85 mg L⁻¹ of the Reactive Orange 16 dye were investigated using a filter-press reactor. The electrolyses were carried out at the flow rate of 7 L min⁻¹, at different current densities (10-70 mA cm⁻²), and in the absence or presence of chloride ions (10-70 mM NaCl). In the absence of NaCl, total decolourisation of the simulated dye wastewater was attained independently of the electrode used. However, the performance of the BDD electrode was better than that of the Ti-Pt/β-PbO₂ electrode; the total decolourisations were achieved by applying only 1.0 A h L⁻¹ and 2.0 A h L⁻¹, respectively. In the presence of NaCl, with the electrogeneration of active chlorine, the times needed for total colour removal were markedly decreased; the addition of 50 mM Cl⁻ or 35 mM Cl⁻ (for Ti-Pt/β-PbO₂ or BDD, respectively) to the supporting electrolyte led to a 90% decrease of these times (at 50 mA cm⁻²). On the other hand, total mineralization of the dye in the presence of NaCl was attained only when using the BDD electrode (for 1.0 A h L⁻¹); for the Ti-Pt/β-PbO₂ electrode, a maximum mineralization of 85% was attained (for 2.0 A h L⁻¹). For total decolourisation of the simulated dye wastewater, the energy consumption per unit mass of dye oxidized was only 4.4 kWh kg⁻¹ or 1.9 kWh kg⁻¹ using the Ti-Pt/β-PbO₂ or BDD electrode, respectively. Clearly the BDD electrode proved to be the best anode for the electrooxidative degradation of the dye, either in the presence or absence of chloride ions.     

Voltammetric determination of ascorbic acid and dopamine in the same sample at the surface of a carbon paste electrode modified with polypyrrole/ferrocyanide films

Functionalized polypyrrole film were prepared by incorporation of [Fe(CN)₆]⁴⁻ as a doping anion, during the electropolymerization of pyrrole onto a carbon paste electrode in an aqueous solution by potentiostatic method. The electrochemical behavior of dopamine (DA) and ascorbic acid (AA) in one solution was studied at the surface of bare and modified carbon paste electrodes using cyclic voltammetry (CV), linear sweep voltammetry (LSV) and differntial pulse voltammetry (DPV) methods. The well separated anodic peaks for oxidation of DA and AA were observed at the surface of the modified carbon paste electrode under optimum condition (pH 6.00), which can be used for determination of these species simultaneously in mixture by LSV and DPV methods. The linear analytical curves were obtained in the ranges of 0.10-1.00 mM and 0.10-0.95 mM for ascorbic acid and 0.10-1.20 mM and 0.20-0.95 mM for dopamine concentrations using LSV and DPV methods, respectively. The detection limits (2σ) were determined as 3.38 × 10⁻⁵ M and 1.34 × 10⁻⁵ M of ascorbic acid and 3.86 × 10⁻⁵ M and 1.51 × 10⁻⁵ M of dopamine by CV and DPV methods.     

In situ FTIRS and EQCM studies of glycine adsorption and oxidation on Au(1 1 1) electrode in alkaline solutions

Dissociative adsorption and oxidation of glycine on Au(1 1 1) single crystal electrodes in alkaline solutions were studied in the present paper using cyclic voltammetry (CV), in situ FTIR spectroscopy (FTIRS) and electrochemical quartz crystal microbalance (EQCM). In situ FTIRS results demonstrated that adsorbates derived from glycine dissociative adsorption are adsorbed cyanide anions (CN_ad⁻). The CN_ad⁻ species are stable on Au(1 1 1) surface in the potential region from −0.8 to 0.0 V, and can be oxidized when electrode potential is increased above 0.1 V. The oxidation of CN_ad⁻ releases surface active sites for further glycine oxidation. The products of CN_ad⁻ oxidation were determined by in situ FTIRS as cyanate (OCN⁻), aurous cyanide (AuCN) and aurous di-cyanide (Au(CN)₂⁻). The formation of Au(CN)₂⁻ may initiate a dissolution of Au(1 1 1) surface atoms, which has been confirmed by a loss of surface mass determined in EQCM studies. It has revealed also that at high electrode potential region glycine may be split on Au(1 1 1) surface to form AuCH₂NH₂ and AuCOO⁻ adsorbates. Further oxidation of these species yielded CO₂ and -NH₂, and the AuCH₂NH₂ may be also combined with surface Au oxide to form methylamine. The CO₂ species produced in glycine oxidation are all retained in alkaline solutions to generate carbonate (CO₃²⁻) and bicarbonate (HCO₃⁻) species that were clearly determined by in situ FTIRS studies.     

Characterization of electrochemiluminescence of tris(2,2′-bipyridine)ruthenium(II) with glyphosate as coreactant in aqueous solution

Glyphosate, a phosphorus-containing amino acid type herbicide was used as a coreactant for studying of electrochemiluminescence (ECL) reaction of tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy)₃²⁺] in an aqueous solution. In a phosphate buffer solution of pH 8, glyphosate itself was known to be electrochemically inactive at glassy carbon electrode, however, it participated in a homogeneous chemical reaction with the electrogenerated Ru(bpy)₃³⁺, and resulted in producing Ru(bpy)₃²⁺ species at the electrode surface. Kinetic and mechanistic information for the catalysis of glyphosate oxidation were evaluated by the steady-state voltammetric measurement with an ultramicroelectrode. The simulated cyclic voltammogram based on this mechanism was in good agreement with that obtained experimentally. ECL reaction of Ru(bpy)₃²⁺/glyphosate system was found to be strongly dependent on the media pH. In a pH region of 5-9, an ECL wave appeared at ca. +1.1 V vs. Ag/AgCl, which was caused by the generation of *Ru(bpy)₃²⁺ via a Ru(bpy)₃³⁺-mediated oxidation of glyphosate. When pH >10, a second ECL wave was observed at ca. +1.35 V vs. Ag/AgCl, which was believed to be associated with a reaction between Ru(bpy)₃³⁺ and the species from direct oxidation of GLYP at a GC electrode surface.     

In situ radiotracer and voltammetric study of the formation of surface adlayers in the course of Cr(VI) reduction on polycrystalline and (1 1 1) oriented platinum

This paper is focused on the in situ radiotracer and voltammetric studies of the induced HSO₄⁻/SO₄²⁻ adsorption at Pt(poly) and Pt(1 1 1) surfaces in 0.1 mol dm⁻³ HClO₄ solution in the course of Cr(VI) electroreduction. Besides this, the sorption behavior of HSO₄⁻/SO₄²⁻ ions on bare Pt(poly) and Pt(1 1 1) electrodes is compared and discussed. From the experimental results it can be stated that: (i) although the extent of bisulfate/sulfate adsorption is strongly dependent upon the crystallographic orientation of Pt surfaces, the maximum coverage on the Pt(1 1 1) does not exceed 0.2 monolayer; (ii) the Cr(VI) electroreduction on both poly- and (1 1 1) oriented platinum proceeds via a ce (chemical-electron-transfer) mechanism to yield Pt surfaces covered with intermediate surface adlayers containing Cr(VI) particles (and reduced Cr-containing adspecies) and ‘strongly bonded’ HSO₄⁻/SO₄²⁻ ions; (iii) while the coverage of platinum surfaces by the intermediate complexes formed in the course of Cr(VI) electroreduction at E > 0.20 V is basically independent of the crystallographic orientation of the Pt electrode, the onset for rapid Cr(VI) reduction is highly affected by the nature and crystallographic orientation of the electrode.     

Highly salicylate-selective membrane electrode based on a new thiomacrocyclic Schiff base complex of binuclear copper(II) as neutral carrier

New binuclear metallic complexes of thiomacrocyclic Schiff base, 3,9,13,19 -tetraphenyl-6,16-dithione-1,11-dithio-4,5,7,8,14,15,17,18-octaazacycloeicosa-3,8,13,18-tetraene binuclear metal(II) [M(II)₂-TDDOCT] (M = Cu, Co, Ni), were synthesized and their anion response characteristics were investigated. The performances of the electrodes are considerably influenced by the nature of the central metals. The Cu(II) complex-based electrode exhibited a good selectivity to salicylate anion with an anti-Hofmeister selectivity pattern: Sal⁻ > ClO₄⁻ > SCN⁻ > I⁻ > Benzoate > B_r⁻ > Acetate > F⁻ > SO₃²⁻ > NO₂⁻ > Cl⁻ > NO₃⁻ > SO₄²⁻ > H₂PO₄⁻. The electrode had an excellent linear response to Sal⁻ from 9.0 × 10^− 7 to 1.0 × 10^− 1 M with a slope of − 59.3 mV per decade,a detection limit of 5.0 × 10^− 7 M, and a fast response time within 15 s over the entire concentration series in phosphate buffer solutions of pH 5.0 at 25 °C. Spectroscopic techniques and the influence of lipophilic charged additives on the electrode behavior were used to investigate the response mechanism to Sal⁻. The electrode can be applied to the direct determination of salicylate in human urine and pharmaceutical samples and the results obtained are in accord with the results from a standard method.     

The impedance of fast charge transfer reactions on boron doped diamond electrodes

Reversible charge transfer on boron doped diamond (BDD) electrodes was studied using cyclic voltammetry and electrochemical impedance spectroscopy. Polycrystalline diamond films of 5 μm thickness with 200 and 3000 ppm boron content were prepared by chemical vapour deposition on niobium substrate. The samples were mounted in a Teflon holder and used as rotating disk electrodes (RDE) with rotation frequencies between 0 and 4000 rpm. The electrochemical measurements were carried out in aqueous electrolyte solutions of 0.5 M Na₂SO₄ + 5 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆] and 0.1 M KCl + 5 mM [Ru(NH₃)₆]Cl₂/[Ru(NH₃)₆]Cl₃. The electrochemical redox behaviour of the BDD electrodes was found to differ significantly from that of an active Pt electrode. The deviations are indicated by a large peak potential difference and a shift of the peak potentials in cyclic voltammograms with increasing sweep rate. At rotating electrodes lower limiting current densities are found and the impedance diagrams exhibit an additional capacitive impedance element at high frequencies. The results are described quantitatively by an impedance model which is based on partial blocking of the diamond surface.     

Electrochemiluminescence of luminol in dimethyl sulfoxide at a polycrystalline gold electrode

The electrochemiluminescence (ECL) behavior of luminol in oxygen-saturated dimethyl sulfoxide (DMSO) solution at a polycrystalline gold electrode was studied under conventional cyclic voltammetric (CV) conditions. Corresponding to the reduction processes of oxygen, one ECL peak (ECL-1 at −1.40 V versus SCE) with two shoulders (S_1-1 at −0.55 V and S_1-2 at −0.90 V) was observed on the curve of ECL intensity versus potential. Corresponding to the subsequent oxidation processes of oxygen-containing species generated by the reduction of oxygen, one ECL peak (ECL-2 at −0.34 V) with a shoulder (S₂ at −0.67 V) was found. Among them, ECL-2 was strongest; it was 10 times stronger than ECL in pH 13.0 aqueous alkaline solution under the same conditions. These ECL peaks and shoulders were found to depend on the presence of N₂ and O₂, potential scan range, water concentration, supporting electrolyte, and the concentration of luminol. The emitter of both ECL peaks was identified as 3-aminophthalate (AP²⁻) by analyzing the ECL spectra. The origin for these ECL peaks is proposed to be related to the reactions of luminol with various oxygen-containing species such as O₂⁻, H₂O₂, OH⁻ and O₂ electrogenerated by the redox reactions of dissolved oxygen at different potentials. The results indicate that the ECL of luminol was correlated to the redox behavior of oxygen in DMSO. The present work reveals that the solvent plays an important role in the ECL behavior of luminol.