A potentiometric multisensor system for determining lysine in aqueous solutions containing potassium and sodium chloride

A potentiometric multisensor system has been developed for the determination of lysine in aqueous solutions containing sodium and potassium chlorides. The sensor array includes a cross-sensitive sensor, the response of which is the Donnan potential at the ion-exchange polymer/test solution interface, a set of ion-selective electrodes, and a silver-silver chloride reference electrode. Multidimensional regression analysis has been employed for the calculation of component concentrations. The relative error of determining lysine, potassium, and sodium did exceed 10% in the tested solutions.     

Determination of the ionic composition of perfluorinated sulfocationite membranes based on Donnan potential estimates

An express method for determination of the membrane ionic composition is developed based on the possibility of estimating the Donnan potential difference on the individual studied-solution/membrane interface. The Donnan potential is assessed using a new device one end of which serves as the ion-selective electrode sensor. The ionic composition of perfluorinated sulfocationite membranes is determined in systems with mixed inorganic electrolyte solutions by comparing the Donnan potentials in a given system and the reference system. As the reference, a system with perfluorinated sulfocationic membrane and individual potassium chloride solutions is used. The time of one measurement does not exceed 10–15 min. The accuracy and sensitivity of determination were 3% and 0.02 mmol/g, respectively.     

Potentiometric determination of lysine in aqueous solutions using MF-4SK modified perfluorinated membranes

A selective potentiometric sensor was developed on the basis of MF-4SK modified perfluorinated sulfonic cation-exchange membranes for determining lysine monohydrochloride in mixed aqueous solutions of neutral amino acids. It was shown that the treatment of MF-4SK membranes in ethylene glycol increased the sensitivity of the sensor. The use of MF-4SK perfluorinated sulfonic cation-exchange membranes for determining lysine in aqueous solutions is based on a protolytic reaction; as a result of this reaction, single-charged lysine ions from solution are transferred into doubly charged ions in the membrane phase. The Donnan potential at an individual boundary between the studied solution and the membrane is the sensor response. The response time was 10–15 min. The concentration constants of the sensor selectivity to lysine in the presence of glycine, alanine, and leucine did not exceed 0.019. The relative error of determining lysine monohydrochloride in the studied solutions of neutral amino acids was 2–5%.     

Catalytic phenomena during the methanol oxidation at platinum electrodes in contact with solid polymer electrolytes

The methanol electrooxidation at platinum-gauze electrodes contacting a solid polymer electrolyte is studied in water and sulfuric-acid solutions by voltammetry in a broad potential range and by measuring steady-state currents and electrode coverages with chemisorbed species at low anodic potentials. The specific rate of the methanol oxidation in these systems is higher than that of similar platinum electrodes in liquid electrolytes. The catalytic action depends on the measurements conditions and the electrode potential. Reasons for catalytic effects at different potentials are discussed.     

Electrochemical Determination of NDPhA via its Electrocatalysis at Porous Au Electrode in Room Temperature Ionic Liquid

N‐Nnitrosodiphenylamine (NDPhA) is a typical kind of nonvolatile nitrosamine. Its electrochemical oxidation occurs usually at relative positive potentials (>1.1 V) even at catalytic noble metal electrodes in aqueous solutions. The formation of oxide and evolution of oxygen at such high potentials makes the analysis of NDPhA on noble metal electrodes difficult. Accordingly, its electrochemical analysis is usually performed in anhydrous organic electrolytes. In this work, room temperature ionic liquid [BMIM⁺] [BF ] acting as electrolyte was introduced in this electrochemical analysis systems. It acts as supporting electrolyte itself, has good solubility of organic compounds, and allows a wide performance potential window of noble electrode, and in turn, highly electrocatalytic noble electrode of platinum or gold can be used as working electrodes. After the investigation of the electrocatalytic behavior of NDPhA at a gold electrode in this room temperature ionic liquid electrolyte, high sensitive determination of NDPhA was designed. It is demonstrated that the electrochemical response of NDPhA is determined by a surface‐controlled process. Therefore, a sensor with high sensitivity was constructed by applying porous Au electrodes with highly electrocatalytic activity and large active surface area. The present approach on one hand broadens the application field of room temperature ionic liquids, and on the other hand provides a sensitive analytical method for environmental detection.     

The electrodeposition of magnesium using solutions of organomagnesium halides,amidomagnesium halides and magnesium organoborates

The electrochemical behaviour of three groups of electrolyte systems having the ability of electrochemical magnesium deposition, were investigated against the background of galvanotechnical or battery application. Solutions of organomagnesium halides, amidomagnesium halides and magnesium organoborates dissolved in tetrahydrofuran were characterized in terms of conductivity, reversibility of the magnesium deposition process and stability of the electrolytes versus irreversible oxidation. Furthermore the open circuit potential of a magnesium electrode in contact with these electrolytes was measured versus a Ag/Ag⁺ reference electrode. A high reoxidation efficiency was found for magnesium electrodeposited from solutions of organomagnesium halides and amidomagnesium halides. The solutions of magnesium organoborates were superior in terms of electrical conductivity and oxidation stability, the process of magnesium electrodeposition and reoxidation, however turned out to be poor.     

Comparative electrochemical study of self-assembly of octanethiol from aqueous and aqueous ethanol solutions on a gold electrode

The self-assembly of octanethiol (OT) on the surface of a polycrystalline gold electrode in aqueous and aqueous ethanol thiol-containing (1 × 10^–4 М) 0.1 М NaClO₄ solutions was studied. The blocking properties and electrochemical stability of monolayer OT films were studied by chronopotentiometry during OT adsorption under the open circuit conditions (chronoamperometry at a fixed potential) combined with cyclic voltammetry for modified Au/OT electrodes. It was found from the change in the rate of electrochemical reactions in the range of monolayer stability potentials that in aqueous media, compact insulating OT monolayer films formed at a open circuit potential within ~100 s, and the shift of the adsorption potential toward negative values (to–0.6 V) allowed a considerable decrease in the monolayer self-assembly time. The potential shift toward higher negative values (–0.9 V) leads to a removal of OT from the electrode surface during the reductive desorption, with a multipeak current signal recorded on the voltammograms. A transition from aqueous to aqueous ethanol solutions accelerated the formation of an insulating OT monolayer (≈6 s) and led to a change in the shape of the desorption current peak, whose value was almost independent of the ОТ accumulation time and potential.     

Microgravimetric study of electrochemically controlled nucleophilic addition of sulfite to polyaniline

The sulfonation of polyaniline (PANI) films by nucleophilic addition of sulfite ion has been controlled through the polymer oxidation state under electrochemical control. The process was monitored by in situ electrochemical quartz crystal microbalance (EQCM), and the polymer oxidation was accomplished by electrode potential steps in sulfite aqueous solutions. The nucleophilic addition of sulfite to PANI only takes place on the oxidized polymer. From the ratio of added mass to the injected charge, the degree of sulfonation has been obtained with a yield as high as 50%. It has been observed that the ion-exchange mechanism during the oxidation-reduction process in the resulting sulfonated polymer is analogous to the polymer produced by electrophilic sulfonation of polyaniline or by copolymerization of aniline with aminosulfonic acids, unlike the ionic exchange observed for unmodified PANI.     

Electrochemical behavior of nickel in electrolytes based on 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid for capacitor applications

Electrochemical studies were performed using Ni electrodes in solutions of a mixture of ethylene glycol or of γ-butyrolactone with 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid. The aim of the study was to evaluate the use of these systems in electrochemical double-layer capacitor. Cyclic voltammetry experiments showed a potential range at which the Ni electrode behaved as a polarizable electrode. Ni oxidizes at high anodic potentials. Inside the potential range without electrochemical activity, the capacitance and the solution resistance, which were evaluated by impedance electrochemical spectroscopy, were compared for the two solutions tested. Conductivity measurements of the electrolytes with different compositions were also acquired. The results of cyclic voltammetry indicated that the Ni has a wide electrochemical window and low current peak densities of oxidation in the γ-butyrolactone medium than in ethylene glycol medium. The γ-butyrolactone and 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid solutions had the highest conductivity values. Decreased 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid content in different solvent mixtures resulted in an increase in the capacitance value at the Ni/electrolyte interface. The highest capacitance values were obtained for Ni in ethylene glycol and 1-n-butyl-3-methylimidazolium tetrafluoroborate medium.     

锂/聚合物电解质电化学固/固界面的研究

综述了聚合物锂电池中锂/聚合物电解质电化学固/固界面的研究进展。通过与锂/液体电解质体系进行比较,简要介绍了在锂/聚合物电解质界面上发生的电化学反应、锂钝化层形成及其对界面反应的影响,并侧重讨论了传统电化学方法和谱学方法,特别是现场分析技术在电化学固/固界面研究中的应用。总结了锂/聚合物电解质界面的几种不同改善途径。     

The electrochemistry of antibody-modified conducting polymer electrodes

The modification of conducting polymer electrodes with antibodies (i.e. proteins) by means of electrochemical polymerization is a simple step that can be used to develop an immunological sensor. However, the electrochemical processes involved leading to the generation of analytical signals by the sensor have not been fully investigated. In this work, we report on the characterization of the interaction between an antigen, human serum albumin (HSA) and an antibody-immobilized polypyrrole electrode (such as anti-HSA) using cyclic voltammetry (CV) and impedance spectroscopy. This interaction was monitored using electrochemical impedance spectroscopy at three different potentials. The potentials correspond to the three redox states of the electroconducting polymer (i.e. reduced, doped and overoxidized states). Evidence from the CV experiments confirmed that there was a shift in the potential, which was found to be proportional to the concentration. Both the CV and the impedance experiments indicated that this potential-dependent shift could be attributed to antibody–antigen (Ab–Ag) binding.     

Influence of aqueous electrolytes on the wetting behavior of hydrophobic solid polymers-low-rate dynamic liquid/fluid contact angle measurements using axisymmetric drop shape analysis

The interaction of inorganic ions with low-energy hydrophobic surfaces was examined using model systems of solid polymers without ionizable functional surface groups in aqueous electrolyte solutions. Low-rate dynamic contact angle measurements with captive bubbles in conjunction with axisymmetric drop shape analysis (ADSA) were performed to study the influence of electrolyte ions (in the aqueous test solutions) on the wettability of the polymers. When various types of ions were used, no significant change in advancing and receding contact angles was observed. The contact angle hysteresis was small. The zeta potential of the model polymers in aqueous electrolyte solutions was determined from streaming potential measurements. The variation of the zeta potential at different pH levels indicates preferential adsorption of hydroxyl ions at this interface. However, the presence of electrolytes at the interface between water and the different model polymers did not influence the macroscopic contact angle. The results may suggest the absence of any specific interaction between the ions and the solid polymer, as this should result in changes of hydrophobicity. Similar to the air/water interface, the composition and the potential of the polymer/water interface are obviously determined predominantly by the aqueous phase with only slight influence from the solid phase.     

Potentiometric cross-sensitive PD sensors for the simultaneous determination of nicotinic acid and pyridoxine hydrochloride in aqueous solutions

A potentiometric multisensory system is developed for the rapid simultaneous determination of pyridoxine hydrochloride and nicotinic acid in aqueous solutions. Sensors for which analytical signal is constructed by the Donnan potential are used within a multisensory system as cross-sensitive elements. In solutions containing both components in concentrations from 1.0 × 10^?4 to 1.0 × 10^?2 M, the relative error of analysis did not exceed 10%. Standard titrimetry and spectrophotometry methods were used for the reference analysis of the target vitamins in multicomponent solutions.     

Electrolyte effects on electrochemical properties of osmium complex polymer modified electrodes.

The electrolyte effects on the electrochemical behaviors of osmium complex polymer modified electrodes were investigated by a comparison between two osmium complexes, [Os(bpy)2(PVI)10Cl]Cl (Os-PVI10) and [Os(bpy)2(PVP)10Cl]Cl (Os-PVP10). The electrode process at Os-PVI10 modified electrodes is reaction-controlled, while a diffusion-controlled electrode process exists at Os-PVP10 modified electrodes. Both the cation and anion in supporting electrolytes strongly affect their electrochemical behaviors, such as the redox potential, wave shape and peak current. These phenomena are attributed to a change in the film structure and polymer swelling in various supporting electrolytes. The influence of electrolyte anions on the electrochemical behaviors is related to their hydrophobicity. The electrode process of Os-PVP10 depends on the pH value of solutions, exhibiting different electron transfer mechanisms.     

Electrochemical Detection of Melamine

Poly(caffeic acid) polymer was immobilized onto the surface of a glassy carbon electrode via electropolymerization. Voltammetry shows a signal related to the two‐electron oxidation of the immobilized hydroquinone groups in the caffeic acid monomer units. The modified electrode in aqueous solution shows complexation of the electrogenerated o‐quinone species with melamine thus allowing in the electrochemical detection of melamine by recording the shift in potential of the oxidation signal of the polymer. Melamine detection was investigated in pure aqueous solutions and in the presence of milk powder solutions and the proposed analytical method of melamine detection in milk powder was applied successfully with an average recovery of ca. (91±7.9)%.     

Methanol electrooxidation on platinum mesh electrodes bonded to solid polymer electrolytes

Methanol electrooxidation on smooth platinum electrodes bonded to solid polymer electrolytes was studied in water and acid solution by voltammetric measurements with different scanning rates. An enhancement of the oxidation rates was observed in these systems as compared to identical platinum electrodes in contact with liquid electrolytes. This electrocatalytic effect strongly depends on the measuring conditions and on the electrode potential. The reasons for the catalytic effects at different potentials are discussed. Received: 8 January 1997 / Accepted: 1 December 1997     

汞修饰掺锡三氧化二铟导电玻璃光透薄层电化学池的设计

报道了汞膜修饰掺锡三氧化二铟导电玻璃电极的制备及其薄层电化学池的设计，测试限电极和薄层的光、电化学性能，在水溶液中，与基底电极相比，该电极的负电位范围增加了７００ｍＶ，并表现出普通汞电极的电化学 性质，以此电极制得的电极制得的薄层层池可适用于氧化还原电位较负的电化学过程的光谱电化学研究及金属离子的电化学分析。     

Covalent versus Electrostatic Strategies for Nanoparticle Immobilisation

We demonstrate that in neutral electrolytes, a polyelectrolyte‐based (ω‐mercaptoacid/poly‐L ‐lysine) immobilisation strategy for as‐prepared electrostatically stabilised metal nanoparticles is a powerful alternative to often difficult to control dithiol approaches. Our data confirm straightforward preparation of high‐coverage nanoparticle electrodes with fast kinetics and an electrochemical window of up to 1.5 V even in unbuffered solutions, under both stationary and hydrodynamic conditions. The stability region is limited by reductive desorption of the mercaptocarboxylic acid at negative potentials, and by nanoparticle oxidation at positive potentials. The electrostatic immobilisation is valuable for the study of electroanalytical and electrocatalytic processes using nanoparticulate electrode materials.