Synthesis and characterization of monoazathiacrown ethers as ionophores for polymeric membrane silver-selective electrodes

Nine monoazathiacrown ethers have been synthesized and explored as ionophores for polymeric membrane Ag⁺-selective electrodes. Potentiometric responses reveal that the ion-selective electrodes (ISEs) based on 2,2′-thiodiethanethiol derivatives can exhibit excellent selectivities toward Ag⁺. The plasticized poly(vinyl chloride) membrane electrode using 22-membered N₂S₅-ligand as ionophore has been characterized and its logarithmic selectivity coefficients for Ag⁺ over most of the interfering cations have been determined as <−8.0. Under optimal conditions, a lower detection limit of 2.2 × 10⁻¹⁰ M can be obtained for the membrane Ag⁺-ISE.     

Voltammetric studies on the potent carcinogen, 7,12-dimethylbenz[a]anthracene: Adsorptive stripping voltammetric determination in bulk aqueous forms and human urine samples and detection of DNA interaction on pencil graphite electrode

7,12-Dimethylbenz[a]anthracene (DMBA), is a widely studied polycyclic aromatic hydrocarbon that has long been recognized as a very potent carcinogen. Initially, the electrochemical oxidation of DMBA at the glassy carbon and pencil graphite electrodes in non-aqueous media (dimethylsulphoxide with lithium perchlorate) was studied by cyclic voltammetry. DMBA was irreversibly oxidized in two steps at high positive potentials, resulting in the ill-resolved formation of a couple with a reduction and re-oxidation wave at much lower potentials. Special attention was given to the use of adsorptive stripping voltammetry together with a medium exchange procedure on disposable pencil graphite electrode in aqueous solutions over the pH range of 3.0-9.0. The response was characterized with respect to pH of the supporting electrolyte, pre-concentration time and accumulation potential. Using square-wave stripping mode, the compound yielded a well-defined voltammetric response in acetate buffer, pH 4.8 at +1.15 V (vs. Ag/AgCl) (a pre-concentration step being carried out at a fixed potential of +0.60 V for 360 s). The process could be used to determine DMBA concentrations in the range 2-10 nM, with an extremely low detection limit of 0.194 nM (49.7 ng L⁻¹). The applicability to assay of spiked human urine samples was also illustrated. Finally, the interaction of DMBA with fish sperm double-stranded DNA based on decreasing of the oxidation signal of adenine base was studied electrochemically by using differential pulse voltammetry with a pencil graphite electrode at the surface and also in solution. The favorable signal-to-noise characteristics of biosensor resulted in low detection limit (ca. 46 nM) following a 300-s interaction. These results displayed that the electrochemical DNA-based biosensor could be used for the sensitive, rapid, simple and cost effective detection of DMBA-DNA interaction.     

The electrochemical determination of phenolic derivates using multiple pulsed amperometry with graphite based electrodes

The electrochemical determinations of 4-chlorophenol (4-CP) and 4-nitrophenol (4-NP) by chronoamperometry (CA) and multiple pulsed amperometry (MPA) using expanded graphite-epoxy composite (EG-Epoxy) and rotating spectral graphite disc (SG) electrodes are reported. The electrochemical behaviours of both electrodes in the presence of organics informed about oxidation peak potential and the electrode fouling with organics concentration increasing. Setting up the oxidation peak potential as detection potential, only SG gave good electroanalytical performance using CA. However, by MPA applying both electrodes exhibited the capability to assess electrochemically and quantitatively the pollutants from aqueous solutions. UV spectrometric method detecting 4-CP and 4-NP at λ = 280 nm and λ = 398 nm wavelength, respectively was used for validation and parallel determinations.     

罗丹明B聚合物修饰单壁碳纳米管薄膜电极的制备、表征及一氧化氮活体分析应用

以单壁碳纳米管作为电极材料,基于减压过滤和电聚合方法制备了一种薄膜型一氧化氮(NO)电化学传感器。扫描电镜、红外光谱和电化学交流阻抗表征表明,减压过滤可以制备出导电性好、电分析性能优良的薄膜电极,而罗丹明B能通过电聚合在其表面形成高比表面的纳米敏感结构。这种薄膜型电化学传感器对NO具有灵敏的电化学响应,其安培氧化电流与NO浓度在7.2×10-8~2.5×10-5mol/L范围内呈良好的线性关系,检出限(S/N=3)达3.6×10-8mol/L。将该传感器紧贴在麻醉豚鼠的肝脏表面,成功实现了肝组织细胞在L-精氨酸刺激下NO释放的实时监测。     

Influence of Metal Nanoparticles on the Electrocatalytic Oxidation of Glucose by Poly(NiIIteta) Modified Electrodes

Conductive polymeric [Ni^II(teta)]²⁺ (teta=C‐meso‐5,5,7,12,12,14‐hexamethyl‐1,4,8,11‐tetra‐azacyclotetradecane) films (poly(Ni)) have been deposited on the surface of glassy carbon (GC), Nafion (Nf) modified GC (GC/Nf) and Nf stabilized Ag and Au nanoparticles (NPs) modified GC (GC/Ag‐Nf and GC/Au‐Nf) electrodes. The cyclic voltammogram of the resulting electrodes, show a well defined redox peak due to oxidation and reduction of poly(Ni) system in 0.1 M NaOH. They show electrocatalytic activity towards the oxidation of glucose. AFM studies reveal the formation of poly(Ni) film on the modified electrodes. Presence of metal NPs increases electron transfer rate and electrocatalytic oxidation current by improving the communication within the Nf and poly(Ni) films. In the presence of metal NPs, 4 fold increase in current for glucose oxidation was observed.     

Orthogonal Signal Correction for Voltammetry

The paper presents orthogonal signal correction (OSC) as a useful algorithm to remove undesired signals distortions, connected with the application of solid electrodes in voltammetry which currently replace toxic mercury sensors due to metal toxicity. It was proven that the influence of additive, multiplicative and typical non‐linearity perturbations of the signal for a calibration model may be substantially limited. Additionally, a noticeable arrangement of the curves was observed which improves the exploration of the analytical system under consideration. The ability of OSC to remove undesirable background effects and improve the quality of results was demonstrated with simulated and experimental data sets.     

Selective Electroanalysis of Ascorbic Acid Using a Nickel Hexacyanoferrate and Poly(3,4‐ethylenedioxythiophene) Hybrid Film Modified Electrode

The mixed‐valent nickel hexacyanoferrate (NiHCF) and poly(3,4‐ethylenedioxythiophene) (PEDOT) hybrid film (NiHCF‐PEDOT) was prepared on a glassy carbon electrode (GCE) by multiple scan cyclic voltammetry. The films were characterized using atomic force microscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, X‐ray diffraction, and electrochemical impedance spectroscopy (AC impedance). The advantages of these films were demonstrated for the detection of ascorbic acid (AA) using cyclic voltammetry and amperometric techniques. The electrocatalytic oxidation of AA at different electrode surfaces, such as the bare GCE, the NiHCF/GCE, and the NiHCF‐PEDOT/GCE modified electrodes, was determined in phosphate buffer solution (pH 7). The AA electrochemical sensor exhibited a linear response from 5×10⁻⁶ to 1.5×10⁻⁴ M (R²=0.9973) and from 1.55×10⁻⁴ to 3×10⁻⁴ M (R²=0.9983), detection limit=1×10⁻⁶ M, with a fast response time (3 s) for AA determination. In addition, the NiHCF‐PEDOT/GCE was advantageous in terms of its simple preparation, specificity, stability and reproducibility.     

Influence of the Electrode Material on the Electrochemical Behavior of Carbon Paste Electrodes Modified with Meldola Blue and Methylene Green Adsorbed on a Synthetic Zeolite

Carbon paste electrodes modified with a phenoxazine derivative, Meldola blue, and a phenothiazine derivative, methylene green, both strongly adsorbed on a synthetic zeolite were investigated using either glassy carbon powder (Sigradur K, SK) or single‐walled carbon nanotubes (SWCNT) as conductive electrode material. In the case of SWCNT based electrodes, the formal potential of both mediators was pH dependent, as expected for a redox process involving proton transfer. In contrast, the formal potential of both mediators of SK based modified electrodes was practically insensitive to pH. This behavior is discussed in terms of interactions existing in the heterogeneous system mediator‐zeolite‐electrode material.     

Nafion Coated Silver Amalgam Electrode for Determination of Trace Metals by Anodic Stripping Voltammetry

This paper describes characterization and application of Nafion coated solid silver amalgam electrodes to prevent surface fouling of surfactants in determination of trace metals by differential pulse anodic stripping voltammetry (DPASV). Polymer films of different thickness were tested using Nafion solutions in the range 0.25%–1%. Optimum thickness was archived using a 0.5% Nafion solution, resulting in both increased response and stability over time compared to uncoated electrodes. The influence of model surface active macromolecules was studied using triton X‐100, sodium dodecyl sulfate, dodecyl pyridinium chloride and bovine serum albumin as representatives for surfactants. The resistance to surfactants makes the studied Nafion coated solid silver amalgam electrodes an interesting alternative for practical use in environmental monitoring.     

Hot Electron Induced Cathodic Electrochemiluminescence at Disposable Screen Printed Carbon Electrodes

Hot electron induced cathodic electrochemiluminescence (ECL) was observed at screen printed carbon electrodes (SPCEs) during pulse polarization. The thin insulating film resulted from the printing inks was found to be suitable for generating hot electrons, which can further be converted to hydrated electrons and induce the subsequent luminescence. Compared with disposable Al/Al₂O₃ electrode, SPCEs show more stable and reproducible ECL in a wider pH range without background emission. A sensitive ECL method for determination of quercetin is proposed. The detection limit is 8.0×10^?10 mol L^?1(S/N=3), which is two magnitudes lower than that of common ECL method.