Charge transfer across a polymer gel/liquid interface: determination of ionophores

An electrochemical method for the determination of the ionophores monensin and lasalocid was developed, based on the polarization of an agar gel/nitrobenzene electrolyte interface. The measured current corresponding to the facilitated ion transfer across this interface is directly proportional to the concentration of an ionophore dissolved in the organic phase. Using cyclic voltammetry in a three-electrode system the detection limit for both ionophores is about 3 × 10^?5 M.     

Comparative studies on the adsorption and association of 3-methylxanthine and 7-methylxanthine at a charged interface

Summary A systematic comparative study of the adsorption and association of 3-methylxanthine (3MXan) and 7-methylxanthine (7MXan) at mercury-solution interfaces in acidic, neutral, and alkaline buffer solutions was undertaken by ac voltammetry. At bulk concentrations of3MXan above a threshold value, the stacking interactions between vertically oriented molecules lead to a slow reorientation aroundE _ecm, and the molecules adopt a perpendicular orientation. The association of the adsorbed molecules of7MXan is hindered and is not effective in promoting base-base stacking interactions. The enhanced surface activity of3MXan compared to7MXan results from the different position of the methyl group in the purine moiety. The effect of some divalent metal ions on adsorption stages and association of the investigated compounds has been studied. The results indicate that the complexation of methylated xanthine enhances the stacking interactions and hence would be expected to facilitate the formation of perpendicularly stacked layers ofM(II)-MXan complexes on the electrode surface. The adsorption parameters of the investigated compounds have been computed in absence and presence of Cu(II) at differentpH values. The results are compared with the behaviour of xanthine.

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Vergleichende Untersuchungen zur Adsorption und Assoziation von 3-Methylxanthin und 7-Methylxanthin an einer geladenen Grenzfläche

Zusammenfassung Eine systematische vergleichende Untersuchung zur Adsorption und Assoziation von 3-Methylxanthin (3MXan) und 7-Methylxanthin (7MXan) an Quecksilber-Lösungs-Grenzflächen wurde mittels AC-Voltammetrie in sauren, neutralen und basischen Pufferlösungen durchgeführt. Oberhalb einer bestimmten Grenzkonzentration kommt es durch Wechselwirkungen zwischen vertikal angeordneten3MXan-Molekülen zu einer langsamen Reorientierung umE _ecm, was zu einer senkrechten Anordnung führt. Die Assoziation von7MXan ist gehindert und erlaubt daher keine ausgeprägten Basen-Basen-Wechselwirkungen. Die erhöhte Oberflächenaktivität von3MXan gegenüber7MXan resultiert aus der unterschiedlichen Stellung der Methylgruppe am Purinrest. Der Effekt einiger zweiwertiger Metallionen auf die Adsorption und Assoziation von3MXan und7MXan wurde untersucht. Die Ergebnisse weisen auf eine Begünstigung der Wechselwirkungen hin; die Bildung von vertikal angeordneten Grenzschichten an der Elektrodenoberfläche sollte daher im Fall vonM(II)-Mxan-Komplexen erleichtert sein. Die Adsorptionsparameter der untersuchten Verbindungen wurden in Abwesenheit und in Gegenwart von Cu(II) bei verschiedenenpH-Werten berechnet. Die Ergebnisse werden mit dem Verhalten von Xanthin verglichen.

     

Electrochemical Properties of Poly-o-Phenylenediamine Films in Solutions with Variable Concentration of Hydronium Ions

Electrochemical behavior of poly-o-phenylenediamine (PoPhD) films in lithium perchlorate and perchloric acid solutions of different pH and constant ionic strength is studied using cyclic voltammetry, low-amplitude chronoamperometry, chronopotentiometry, and faradaic-impedance spectroscopy. The experimental results point to the diffusion–migration kinetics of charge transfer processes in redox-active PoPhD films and show that two such processes occur during oxidation–reduction of PoPhD. The processes are separated most fully at low concentrations of hydronium ions. Effect of the electrode potential and electrolyte composition on these processes is examined. Different methods yield similar results and permit their more reliable interpretation.     

Comparison of reactivities of 1- and 4-oxotetrahydrocarbazoles in reactions with nucleophilic and electrophilic reagents

The half-wave potentials of polarographic reduction of the carbonyl group in unsubstituted and N-methyl- and N-phenylsulfonyl-substituted 1- and 4-oxotetrahydrocarbazoles and their reactivities in reactions with nucleophilic (NaBH₄, malonodinitrile, and cyanoacetamide) and electrophilic (DMF dimethyl acetal) reagents were compared. 4-Oxotetrahydrocarbazoles are much less reactive than 1-oxotetrahydrocarbazoles. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1832–1836, August, 2005.     

Electrochemical study of triphenyltin piperidyl dithiocarbamate

The reduction of triphenyltin piperidyl dithiocarbamate in acetone has been investigated using d.c. polarography and cyclic voltammetry. Polarographic reduction yielded four well-defined waves, two of which were diffusion-controlled and two of which appear to represent adsorption processes. The cyclic voltammetric study yielded results in close agreement with the polarographic data. Results appear to indicate the release of the dithiocarbamate moiety, followed by reduction to form the triphenyltin radical, which undergoes dimerization, as well as reduction to the triphenyltin anion. For comparison, the polarographic reduction of triphenyltinchloride was investigated. A mechanism similar to that proposed by earlier authors for the polarographic behaviour of tributyltin oxide was found. For convenience, the more commonly used terminology of piperidyl dithiocarbamate is used throughout the paper, in place of (piperidine-1-carbodithioato) triphenyltin (IV).     

Decomposition of vegetables for determination of Zn,Cd, Pb and Cu by stripping voltammetry

A simple and accurate digestion method using nitric acid, perchloric acid and hydrogen peroxide has been developed for use in trace analysis for heavy metals in vegetables by differential pulse anodic stripping voltammetry. The recovery of the metals from the samples is lower if the hydrogen peroxide is omitted from the digestion mixture. Standard reference materials have been analysed satisfactorily by this method.     

电化学免疫分析法研究进展

电化学免疫分析法是将免疫分析与电化学分析技术相结合的一种免疫分析新方法，近十多年来，电化免疫分析的研究有了迅速的发展。本文对电化学的免疫分析法的标记物、免疫方法、电化学检测技术进行了概括总结，并展望了电化学免疫分析的发展前景。     

壳聚糖修饰玻碳电极卷积伏安法测定环境水中的EDTA

制备了壳聚糖修饰玻碳电极 ,研究了Fe(EDTA) -在修饰电极上的吸附还原行为 ,用卷积伏安法通过Fe(EDTA) -的检测测定了环境水中的EDTA。在优化的实验条件下 ,峰电流值与 8.0× 1 0 -7～ 5 .0× 1 0 -6mol L的EDTA呈线性关系 ,回归方程为epp′ =0 .75 2 5c - 0 .661 3,r =0 .991 ,最低检出限为 5 .0× 1 0 -7mol L ,5次测定的相对标准偏差小于 5 .8%。对实际样品测定的回收率为98 1 %～ 1 0 5 % ,对比HPLC的结果 ,相对偏差小于 5 %。     

Voltammetric determination of 5-hydroxydole-3-acetic acid in human gastric juice

A method for the determination of the major serotonin metabolite — 5-hydroxyindole-3-acetic acid (5-HIAA) in human gastric juice by cyclic voltammetry was described. The measurement conditions were investigated. The potential window was chosen from +0.1 to +0.9 V, the supporting electrolyte was 0.025 M PBS solution (pH 2.0). The method allowed determination in the concentration range from 2.0 ×10⁻⁷ to 2.0 ×10 ⁻⁵ M and a detection limit of 80 nM. When samples of gastric juice were analyzed with the method, we obtained the mean content of 5-HIAA in the gastric juice. Meanwhile, interference from other ions and substances were examined. The experimental results indicate that the method for the determination of gastric juice samples is successful.     

Amperometric detection of hydrazine by cyclic voltammetry and flow injection analysis using ruthenium modified glassy carbon electrodes

Glassy carbon electrodes modified with (5-amino-1,10-phenanthroline)bis(bipyridine)ruthium(II) chloride hydrate, [(bpy)₂Ru(5-phenNH₂)]Cl₂·H₂O, are shown to oxidize hydrazine with excellent sensitivity. The presence of an amine group on the ruthenium complex facilitates electropolymerization onto the electrode surface. Using cyclic voltammetry, a large catalytic current is observed upon oxidation of hydrazine in phosphate buffer (pH 5.0), compared to the current obtained from the ruthenium-modified electrode with no hydrazine present. The sensitivity of cyclic voltammetry is sufficient for obtaining a linear calibration curve for hydrazine over the range of 10⁻⁵ to 10⁻² M. Hydrodynamic amperometry was used to determine the working potential for flow injection analysis. The limit of detection for hydrazine was determined to be 8.5 μM using FIA. The thickness of these films was shown to increase linearly with the number of electropolymerization cycles, in the range of 1000-2500 nm for 5-20 cycles, respectively, using Rutherford backscattering spectrometry (RBS). RBS analysis also suggests that the film is multilayered with the outermost layers containing a high ruthenium concentration, followed by layers where the concentration of ruthenium decreases linearly and approaches zero at the electrode surface.