Adsorptive Voltammetry of Polyelectrolyte Complex Between 11‐Ferrocenyltrimethylundecylammonium and Polyanions at Carbon Paste Electrode

For polyelectrolyte complex between cationic surfactant and polyanion, the adsorptive voltammetry at carbon paste electrode using an electroactive cationic surfactant was examined. The adsorption state of the cationic surfactant in the complexes at CPE was estimated from the half‐height width of the oxidation waves. The half‐height width for poly(styrene sulfonate) was independent of the molecular weight, and was same as that for poly(vinyl sulfate). The half‐height width for heparin was broad and different from that of the vinyl polyanions. According to the analysis by Frumkin isotherm, the interaction between cationic surfactants was attractive in heparin complex at CPE, however, in the vinyl polyanion complexes at CPE the interaction was non‐cooperative as that predicted with the Langmuir isotherm. In spite of the same adsorption state, the concentration dependency of the peak current for poly(styrene sulfonate) was quite different from that for poly(vinyl sulfate). The concentration dependence indicated the reactive property of each polyanion on the association with the cationic surfactant in aqueous solution.     

12-Membered crown ethers. Derivatives of benzo-and naphtho-12-crown-4 and their membrane electrode properties. Part II

A series of lipophilic derivatives of benzo-12-crown-4 and naphtho-12-crown-4 has been synthesized. The behavior of the prepared derivatives in membrane ion-selective electrodes has been studied. Selectivity changes dependent on the position and number of substituents have been observed.     

Thermal decomposition of sodium nitrite and sodium nitrate pre-adsorbed on TiO2 surfaces

The thermal decomposition of sodium nitrite or nitrate pre-adsorbed upon TiO₂ surfaces has been investigated by employing several techniques as infrared spectroscopy (IR) and temperature programmed desorption in conjunction with mass spectrometry analysis (TPD-MS) to study the features observed during these thermal decompositions. Differential thermal analysis (DTA) in combination with X-ray diffraction analysis (XRD) were used to investigate the possibility of a solid state chemical reaction between the solid products originated from the thermal decomposition of the pre-adsorbed species and the TiO₂. On the basis of our results, various characteristic features of these thermal decomposition reactions will be discussed.This work was supported by JUNTA DE ANDALUCIA (financial support for research groups/1990).     

Electrochemical Reduction of Monochlorinated Hydrocarbons at a Hydrophobic Zn/PTFE Composite‐Electroplated Zn Electrode in a Water‐Acetonitrile Mixture

Composite‐electroplating of zinc particles with polytetrafluoroethylene at a zinc substrate resulted in a working electrode which could be used at high negative potentials (to ?2.5 V vs. Ag/AgCl) without significant hydrogen evolution. The electrodes were characterized by SEM and CV and were used to detect organochloride compounds in a water‐acetonitrile mixture, by potential step methods.     

Transference numbers for ultra concentrated solutions of aqueous hydrochloric acid at 25°C

Transference numbers of HCl(aq) solutions at 25°C, from 0.01 to 13.6 mol-kg^–1(m) have been obtained by measuring the emf of cells with transference using hydrogen gas/platinum electrodes. Good agreement is obtained at concentrations up to 1 m with all previous data, and our results strongly corroborate those of King and Spiro over the 2–8m concentration range. The transference numbers of the hydronium ion fit the empirical equation, _H ^HCl = 0.821 + 0.0457m ^1/2 – 2.476×10^–2m – 1.90×10^–4 m ² – 1.45×10^–5 m ³ the maximum deviation in T _H ^HCl being 0.003.     

Electrochemical Study of the Interactions of DNA with Redox‐Active Molecules Based on the Immobilization of dsDNA on the Sol‐Gel Derived Nano Porous Hydroxyapatite‐Polyvinyl Alcohol Hybrid Material Coating

A novel type of sol‐gel inorganic‐organic hybrid material coated on glassy carbon electrode used for immobilization of double‐stranded DNA (dsDNA) and study of dsDNA with redox‐active molecules was developed. The hybrid material coating was produced by sol‐gel method with nano hydroxyapatite (HAp)‐polyvinyl alcohol (PVA). The optimum composition of the hybrid material was first examined, and the morphology of the nano HAp‐PVA coatings was investigated with the help of Scanning Electron Microscope (SEM). DsDNA was immobilized in/on the nano HAp‐PVA hybrid coatings by adsorption and the characteristics of the dsDNA/HAp‐PVA/GCE were studied by cyclic voltammetry (CV) using the probes of Co(phen) and Fe(CN) . The results indicate that the dsDNA can be immobilized on the nano porous HAp‐PVA coating effectively and its stability can satisfy the necessity of study on the interactions of dsDNA with redox‐active molecules on the electrode surface. Co(bpy) and Co(phen) were used as the model molecule to study the interactions of dsDNA with redox‐active molecules. Information such as ratio (K_Ox/K_Red) of the binding constant for the oxidized and reduced forms of a bound species, interaction mode, including change in the mode of interaction, and “limiting” ratio K /K at zero ionic strength (μ) can be obtained using dsDNA/HAp‐PVA/GCE with about 2 μg of DNA samples.     

A Sensitive Spectrophotometric Determination of Nitrite in Water and Soil

A highly sensitive spectrophotometric method for the determination of nitrite in water and soil has been developed. The reaction of nitrite with acidified potassium iodide to liberate iodine which oxidizes leuco‐crystal violet (LCV) to form crystal violet having absorption maxima at 590 nm forms the bases of this method. In aqueous medium the system obeys Beer's law in the range of 0.1 to 1.0 μg per 25 mL (0.004–0.04 ppm), while in an extractive system the range is 0.025–0.25 μg in 100 mL (0.00025–0.0025 ppm). The molar absorptivity and Sandell's sensitivity were found to be 1.54 × 10⁶ 1 mol^?1 cm^?1 and 44 pg cm^?2, respectively.     

Electrocatalytic Reduction of Chromium(VI) by Thionin: Electrochemical Properties and Mechanistic Study

The electrochemical properties of aqueous thionin (an electroactive water soluble dye) of pH 1–12 were investigated by cyclic voltammetry at a boron doped diamond(BDD) electrode. A well defined reversible redox couple was observed in acidic, neutral and alkaline solutions. The standard potential and kinetic parameters for thionin were obtained by fitting experimental cyclic voltammograms to those generated by the DigiSim program. The electrogenerated reduced form of thionin has been used as an efficient organic catalyst for the reduction of Cr(VI) at a BDD electrode immersed in aqueous media. The cyclic voltammetry measurements indicate that an electrocatalytic process occurs, where electrochemically generated thionin reduced species (Leucothionin) is oxidized by Cr(VI) back to the parent thionin species via a EC' reaction mechanism. The determination of catalytic rate constant (K_cat) was accomplished again by fitting experimental cyclic voltammograms with simulated ones.     

铜电路板缝腐蚀过程缝隙中pH、Cl-浓度分布的测量

根据铜电路板缝腐蚀特征,研制了阵列式Ag/AgCl、IrO2电极,设计缝隙腐蚀模拟装置,在0.5mol.L-1的NaCl溶液中分别同时原位检测电子线路板缝隙腐蚀过程,缝隙内的氯离子浓度分布、pH分布及其随时间的变化.研究表明,在电子线路板发生缝隙腐蚀的过程中,缝隙内部不同深度的Cl-及H+浓度逐渐增大,且随着与缝口距离的增大而增大,从而导致缝隙腐蚀不断向纵深方向发展.     

Electrochemical Immunoassay for Tumor Marker CA19-9 Detection Based on Self-Assembled Monolayer

A CA19-9 electrochemical immunosensor was constructed using a hybrid self-assembled membrane modified with a gold electrode and applied to detect real samples. Hybrid self-assembled membranes were selected for electrode modification and used to detect antigens. First, the pretreated working electrodes were placed in a 3-mercaptopropionic acid (MPA)/β-mercaptoethanol (ME) mixture for 24 h for self-assembly. The electrodes were then placed in an EDC/NHS mixture for 1 h. Layer modification was performed by stepwise dropwise addition of CA19-9 antibody, BSA, and antigen. Differential pulse voltammetry was used to characterize this immunosensor preparation process. The assembled electrochemical immunosensor enables linear detection in the concentration range of 0.05–500 U/mL of CA19-9, and the detection limit was calculated as 0.01 U/mL. The results of the specificity measurement test showed that the signal change of the interfering substance was much lower than the response value of the detected antigen, indicating that the sensor has good specificity and strong anti-interference ability. The repeatability test results showed that the relative standard deviations were less than 5%, showing good accuracy and precision. The CA19-9 electrochemical immunosensor was used for the actual sample detection, and the experimental results of the standard serum addition method showed that the RSD values of the test concentrations were all less than 10%. The recoveries were 102.4–115.0%, indicating that the assay has high precision, good accuracy, and high potential application value.