Indian Journal of Chemistry

Sect. A: Inorganic, Bio-inorganic, Physical, Theoretical & Analytical

 

VOLUME 42A

NUMBER 4

APRIL 2003

 

 

CONTENTS

Papers

 

Sensors/biosensors, based on screen-printing technology for biomedical applications

J P Hart*, A K Abass, K C Honeychurch, R M Pemberton, S L Ryan & R Wedge

709

Electrochemical and persulphate mediated oxidation of indole-3-ethanol

Rajendra N Goyal*, Anil Kumar &   Priyanka Gupta

719

Voltammetric behaviour of indole at carbon fibre microelectrodes in organic solvents: Application to the determination of indole in food samples

Christian Gómez-Gil, Araceli González-Cortés, Lourdes Agüí, Paloma Yáñez-Sedeño &  José M.Pingarrón*

727

Spectroelectrochemical approach for analysing the reaction kinetic of N,N-dimethyl-p-anisidine cation radical with the neutral molecule in acetonitrile

Munetaka Oyama* & Masashi Goto

733

Electroanalytical adaptation of the classical Ellman’s Assay: Determination of total thiols in incubation media from a biological sample (excised articular cartilage)

Olga Nekrassova, Nathan S Lawrence, Robert B Lee, Jill P G Urban & Richard G Compton*

739

Electroreduction of isophthalaldehyde: An example of simultaneous reduction of two identical electroactive centers

 W J Bover, D Johnson, M S Baymak & P Zuman*

    744

Electrochemical reduction of benzyl bromide in the presence of carbon dioxide

Abdirisak A Isse & Armando Gennaro*

751

Molecular imprinting of antibiotic films for electroanalysis of the dopamine/ascorbate system

Sanda Grosu & Waldemar Gorski*

758

Neural networks approach for simulation of electrochemical impedance diagrams

M Cristea, S Varvara, L Muresan & I C Popescu*

764

Electrochemical behaviour of NAD+-modified carbon paste electrodes

S B Saidman

 

769

The role of anions in the electrochemical behaviour of thick palladium oxide layers —Effect of chloride ions

A E Bolzán

774

Comparison of solid state voltammetry and membrane voltammetry: The reduction of 4,4′,4′′,4′′′-(21H,23H-porphine-5,10,15,20-tetrayl)tetrakis[1-octylpyridinium] tetrabromide immobilised as microcrystalline solid and accumulated into a mesoporous TiO2 phytate membrane

Frank Marken*, Susan M Parkhouse, Lesley A Hoe, Katy J McKenzie, Roger J Mortimer, Steve J Vickers & Natalie M Rowley

782

Determination of electrochemical properties of the adsorbed zearalanone mycotoxin by using cyclic and square wave voltammetry

Patricia Gabriela Molina, María Alicia Zón & Héctor Fernández*

789

Enhanced electrogravimetric detection of DNA hybridization on an electrochemical quartz crystal microbalance

Cheng Qiong, Peng Tuzhi*, Zhang Shenglong & Chatherine F Yang

797

Hydrodynamic chronocoulometric estimation of diffusion coefficients and saturated concentrations of dioxygen in KOH solutions

D Zhang, J F Wu, L Q Mao, T Okajima, F Kitamura, T Ohsaka* & T Sotomura

801

Dynamics of the influence of redox active conducting polymer on  corroding interface

S Shriram, S Karthikeyan, S Pitchumani* & N G Renganathan

807

Mercury selective electrochemical sensor based on a double armed crown ether as ionophore

Vinod K Gupta*, Sudeshna Chandra & Shiva Agarwal

813

Pb(II) sensor based on the membrane of 3,4,4a,5-tetrahydro-3-methylpyrimido-[1,6-a] benzimidazole-1 (2H) thione in PVC matrix

A K Jain*, S M Sondhi & Shefali Rajvanshi

819

Electrooxidation of physostigmine at different electrodes

Bengi Uslu*, İnci Biryol, Melike Kabasakaloğlu & M Levent Aksu

824

Polarographic and voltammetric reduction of some pyrazoline-5-ones in  aqueous and micellar media

Wahid U Malik* & M Joseph

830

Autopolymerization of pyrrole on the silver substrates roughened by an electrochemical method

Yu-Chuan Liu* & Shung-Jim Yang

836

Voltammetric determination of thallium(I) on a prussian blue/cinder paste electrode

Jyh-Myng Zen*, Hsing Ho & Pei-Yan Chen

839

Use of voltammetric methods for the analysis of trace metals in engine oils

 P K Tamrakar & K S Pitre*

843

Electrochemical proof of the single bond character of the N-N bonds in some 1,2,4-triazines

J Ludvika & P Zuman

847

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 709-718

 

 

Sensors/biosensors, based on screen-printing technology for biomedical applications

  J P Hart*, A K Abass, K C Honeychurch, R M Pemberton, S L Ryan & R Wedge

 

This article describes three recent developments from our laboratory, in which screen-printed carbon electrodes have been modified in order to develop sensors/biosensors for analytes of biomedical importance. The analytical applications described are (i) progesterone, (ii) glucose and (iii) haemoglobin determination. For each application, the modification procedure for the base transducer and the sensor/biosensor performance characteristics are described. The potential biomedical application areas for these devices are discussed.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 719-726

 

 

Electrochemical and persulphate mediated oxidation of
indole-3-ethanol

Rajendra N Goyal*, Anil Kumar & Priyanka Gupta

 

The electrochemically driven and persulphate-mediated oxidation of indole-3 ethanol has been studied in phosphate buffers. The electrochemical oxidation is carried out at PGE and a well-defined peak is noticed. The studies reveal that no UV/ vis – absorbing intermediate is generated during electrooxidation of indole-3-ethanol (I). On the other hand, oxidation by persulphate follows pseudo-first-order kinetics having first-order with respect to substrate. This reaction takes place with a second-order rate constant of (0.25 ± 0.01) dm3 mol-1 s-1 . The redox mechanisms of electrochemical as well as chemical oxidation have been suggested and in both the oxidations the major product of oxidation is found as hydroxy dimer (VII).

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 727-732

 

 

Voltammetric behaviour of indole at carbon fibre microelectrodes in organic solvents: Application to the determination of indole in food samples

Christian Gómez-Gil, Araceli González-Cortés, Lourdes Agüí, Paloma Yáñez-Sedeño & José M.Pingarrón*

 

The electroanalytical behaviour of indole at cylindrical carbon fibre microelectrodes (CFMEs) in ethyl acetate containing tetrabutylammonium tetrafluoroborate (TBABF4) as supporting electrolyte, has been reported. Voltammetry of indole is found to be dependent on the analyte concentration, which is attributed to a change in the electrooxidation mechanism at high concentrations. The repetitive cyclic voltammograms for a 2.5´10-3 mol l-1 concentration show oxidative electropolymerization of indole and subsequent deposition of the polymer film on the CFME surface. A square wave voltammetric method for the determination of indole at low concentration levels in ethyl acetate is developed, with a linear range between 1.0´10-6 and 6.0´10-5 mol l-1 and a limit of detection of 4.0´10-7 mol l-1. Unlike Pt electrodes, no application of cleaning pretreatment to the CFME surface is needed. Interferences from 3-methylindole, L-tryptophan, histidine, tryptamine and 3-methylamine have been checked, and also the possibility of using flow-injection with amperometric detection have been evaluated. The voltammetric method at CFMEs, based on direct measurements of the analyte extract in ethyl acetate, is applied to the determination of indole in spiked shrimps and pig back fat samples.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 733-738

 

 

Spectroelectrochemical approach for analysing
the reaction kinetic of N,N-dimethyl-p-anisidine cation radical
with the neutral molecule in acetonitrile

  Munetaka Oyama* & Masashi Goto

 

The decay reactions of N,N-dimethyl-p-anisidine (DMA) cation radical (DMA•+) in acetonitrile (AN) have been  analysed using an electron transfer stopped-flow (ETSF) method. In the ETSF method, DMA•+ is generated by mixing acetonitrile solutions of DMA and tris(p-bromophenyl)amine cation radical (TBPA•+). While DMA•+ is fairly stable without DMA, the decay reactions of DMA•+ have been observed when DMA remained in a large excess with DMA•+ in acetonitrile. Such promotion of the decay reaction is similar to the reactions of N,N-dimethyl-p-toluidine (DMT) cation radical (DMT•+), which we have analysed previously. The rate law determined for the reaction of DMA•+ with DMA, -d[DMA•+]/dt = k [DMA•+] [DMA] (k =8.05 M –1 s-1), indicates that the reaction mechanism is similar to that of DMT•+. By analysing the reactions of DMA•+ with pyridine, it has been confirmed that the reaction mechanism proceeds via the acid-base interaction.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 739-743

 

 

Electroanalytical adaptation of the classical Ellman’s Assay: Determination of total thiols in incubation media from a biological sample (excised articular cartilage)

  Olga Nekrassova, Nathan S Lawrence, Robert B Lee, Jill P G Urban & Richard G. Compton*

 

The total thiols in a medium containing authentic biological sample (articular cartilage) has been determined electrochemically. The detection strategy utilises the electrochemical adaptation of the Ellman’s reaction process via the electrochemically initiated reaction of thiols with diethyl-p-phenylenediamine. The strategy has been examined over a biologically significant pH range and the behaviour observed rationalised. The detection of thiols within the biological sample is shown to proceed with micromolar levels of thiol determined within the sample.

 

 

 

Indian Journal of Chemistry

Vol. 41A, April 2003, pp. 744-750

 

 

Electroreduction of isophthalaldehyde: An example of simultaneous reduction of two identical electroactive centers

W J Bover, D Johnson, M S Baymak & P Zuman*

 

The diprotonated form of isophthalaldehyde is reduced by two electrons to a diradical which, reduced further by two electrons, react with two protons to form a dialcohol. The stability of the diradical is much lower than that observed for ortho- and terephthalaldehydes. In acidic media isophthalaldehyde thus behaves like a simple benzaldehyde at twice the concentration. This course of the electrode process, based on polarographic reduction, has been confirmed by cyclic voltammetry and controlled potential electrolysis using a dropping mercury electrode. The diprotonated molecules of isophthalaldehyde are oriented during the reduction process in such a way that probability of the electron transfer is the same for both groups. In the single protonated form of isophthalaldehyde, the groups protonated at the electrode is reduced in a two-electron process to alcohol. The reduction of the second carbonyl group occurs at more negative potentials. At the time of reduction the molecule is oriented with one CH=OH+ group towards the surface. Investigation of the reduction of the unprotonated form is limited by the reaction of the dicarboxaldehyde with hydroxide ions. Addition of hydroxide ions to carbonyl groups result in geminal diol anions which are oxidized in alkaline solutions in two consecutive two-electron steps. One of the CH(OH)O- groups is then oriented preferably at the electrode surface. In isophthalaldehyde dioxime both protonated oxime groupings are reduced simultaneously in a single, eight-electron step.

 

  

  

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 751-757

 

 

Electrochemical reduction of benzyl bromide in the presence of carbon dioxide

Abdirisak A Isse & Armando Gennaro*

 

The electrochemical reduction of benzyl bromide has been investigated in acetonitrile and CO2-saturated acetonitrile by cyclic voltammetry and controlled-potential electrolysis. Electroreduction of the halide in the absence of CO2 leads to a variety of products, the distribution of which depends on the electrode material, applied potential and proton availability in the medium. The electrocarboxylation processes have been carried out at Hg and graphite cathodes using both a two-compartment cell and an undivided cell with dissolving Al anode. The best results (87% phenylacetic yield) are obtained at Hg in the undivided cell. Catalysis by Co(salen) allows the process to be performed at potentials more positive than those required by direct reduction but gives only poor to moderate yields of acid. Results obtained from experiments carried out with benzyl chloride have been compared with those obtained in the case of benzyl bromide.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 758-763

 

 

Molecular imprinting of antibiotic films for electroanalysis of the dopamine/ascorbate system

Sanda Grosu & Waldemar Gorski*

   

Molecular films of a natural antibiotic lasalocid A have been cast on the surface of glassy carbon electrodes and used for the differentiation of electrochemical signals in the model system composed of dopamine and ascorbate. The best signal resolution is obtained at the films that were prepared by evaporating solvent from a chloroform solution of lasalocid that was equilibrated with an aqueous solution of dopamine. The improved selectivity of such films is ascribed to their enhanced hydrophobicity. The latter is hypothesized to be the result of lasalocid’s compact cyclic conformation, which was imprinted in the solid films by the complexation with dopamine. When operated at a constant potential of 0.20 V, the lasalocid-based dopamine sensors are free of interferences from ascorbate and displayed low detection limits (~70 nM dopamine, S/N=3) in conjunction with fast response times (~0.4 s).

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 764-768

 

 

Neural networks approach for simulation of electrochemical impedance diagrams

M Cristea, S Varvara, L Muresan & I C Popescu*

 

A new approach of data simulation using neural networks (NN) has been proposed for electrochemical impedance spectroscopy, applied for copper electrodeposition from sulphate acidic electrolytes. The trained NN, with data obtained in different experimental conditions (electrode potential and thiourea concentrations), have been used to generate impedance spectra for new electrode potential values, within the investigated potential range, as well as to estimate the maximum frequency value on Nyquist plot, by generating supplementary output data for new frequency values, inside the investigated domain of frequencies.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 769-773

 

 

Electrochemical behaviour of NAD+-modified carbon paste electrodes

S B Saidman

 

The effects of electrochemical pretreatment time on the electrochemical response of NAD+-modified carbon paste electrodes have been analysed. Prolonged pretreatment results in an improvement in the catalysis of NADH oxidation. First, pretreatment produces a remotion of pasting liquid that increases the number of surface sites for NADH oxidation. But this surface activation reaches a limiting value and, at longer pretreatment times, activation is produced by the contribution of reduced surface functionalities.NAD+-modified carbon paste electrodes have also been fabricated by incorporating appropriate quantities of NAD+ directly into the paste mixture. Analogous to solution-phase NAD+, the electrodes constructed in this manner present true surface active groups and are able to catalyse NADH oxidation. Pretreatment does not result in a loss of their electrocatalytic properties.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 774-781

 

 

The role of anions in the electrochemical behaviour of thick
palladium oxide layers—Effect of chloride ions

A E Bolzán

 

The influence of chloride ions on the electrochemical behaviour of palladium oxide films grown at 2.00 V in 1 M H2SO4 + x M HCl (0 < x < 10-5) is investigated by means of voltammetry, rotating ring-disk and potential step techniques. Both voltammetric and current transients electroreduction data show that the presence of Cl- ions accelerate the electroreduction of palladium oxide films. The potential of the electroreduction voltammetric peak increases with the chloride concentration. Cathodic current transients show current maxima related to the presence of a nucleation and growth process. The mechanism of palladium oxide layer electroreduction can be interpreted through the formation of chloride-containing complex species which favours the electroreduction by decreasing the time needed to start the nucleation and growth of the new electroreduced phase. This effect is achieved by the breakdown of the anodic layer. The results are discussed within the frame of data previously obtained for perchlorate, phosphate and sulphate ion-containing solutions.

 

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 782-788

 

 

Comparison of solid state voltammetry and membrane voltammetry:
The reduction of 4,4′,4′′,4′′′-(21H,23H-porphine-5,10,15,20-tetrayl)
tetrakis[1-octylpyridinium] tetrabromide immobilised as microcrystalline solid and accumulated into a mesoporous TiO2 phytate membrane [CD1] 

Frank Marken*, Susan M Parkhouse, Lesley A Hoe, Katy J McKenzie & Roger J Mortimer

 

The tetra-cationic free base porphyrin 4,4′,4′′,4′′′-(21H,23H-porphine-5,10,15,20-tetrayl) tetrakis[1-octylpyridinium]4+ (PTTO4+) shares the properties of both a long alkyl chain containing molecule with hydrophobic shell and a highly charged water soluble molecule with hydrophilic core. As a result, PTTO4+ is only very sparingly water soluble and tends to aggregate on suitable surfaces. It is shown here that the electrochemical reduction of PTTO4+ in aqueous media can be studied either by ‘solid state voltammetry’ or by ‘membrane voltammetry’ methodology with complementary results. When immobilised by adhering the microcrystalline powder to the surface of a basal plane pyrolytic graphite electrode, PTTO4+ exhibits two separate one electron-one proton reduction responses, which are both coupled to chemical follow-up processes (assumed here is a H-shift reaction). Both reduction responses become reversible at sufficiently high scan rates. In contrast, when accumulated into a TiO2 phytate membrane, PTTO4+ exhibits a chemically reversible 2 electron-2 proton reduction response. Upon increasing of the concentration of PTTO4+ in the membrane or upon increasing the thickness of the membrane more complex voltammetric responses are detected. High local ‘concentration’ conditions during solid state voltammetry experiments may be regarded as a limiting case of high concentration membrane voltammetry at very thin membranes.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 789-796

 

 

Determination of electrochemical properties of the adsorbed zearalanone mycotoxin by using cyclic and
square wave voltammetry

Patricia Gabriela Molina, María Alicia Zón & Héctor Fernández*

 

The electro-oxidation of zearalanone adsorbed on glassy carbon electrodes in 20% acetonitrile (ACN) + 80% 1 M HClO4 aqueous solution has been studied for the first time by using cyclic and square wave voltammetry. Experimental results clearly demonstrate the surface nature of the electrochemical reaction. The optimum accumulation potential (Eacc) and optimum accumulation time (tacc) are 0 V and 2 min, respectively. Quantitative determination of zearalone has been performed by Square Wave Voltammetry. Linear calibration curves have been obtained from the net peak current (Ip,n) versus c*ZEA in the concentration range from 2 x 10-7 – 1.5 x 10-5 M with a detection limit of 2 x 10-7 M at a signal to noise ratio of 2:1. Cyclic and square wave voltammograms show an ECirrev mechanism to be the most probable mechanism to describe the surface electrochemical reaction. The dependence between Ip,n and Ep,n on the logarithm of acid bulk concentration indicates a deprotonation reaction to should be the fast follow-up chemical reaction coupled to the initial electron transfer reaction.

 

 

 

Indian Journal of Chemistry

Vol. 41A, April 2003, pp. 797-800

 

 

Enhanced electrogravimetric detection of DNA hybridization on an electrochemical quartz crystal microbalance

Cheng Qionga,b, Peng Tuzhia*, Zhang Shenglonga & Chatherine F Yangc

 

Electrogravimetric amplification with an intercalator Hoechst 33258 on an electrochemical quartz crystal microbalance (EQCM) has been reported  for detecting DNA hybridization. The self-assembled monolayer of a-thioctic acid with carboxy group is first self-assembled on a gold film of the resonator on an EQCM. The probe molecules of ssDNA have then been immobilized onto its surface. Processes of immobilization and hybridization have been examined by a quartz crystal microbalance. When the resonator is reacted with Hoechst 33258, masses of Hoechst molecules intercalate in DNA hybrids and enhance the gravimetric signal. Both electrogravimetric and electrochemical signals of the EQCM are linear with the concentration of target DNA in the range of 10-9 mol L-1.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 801-806

 

 

Hydrodynamic chronocoulometric estimation of diffusion coefficients and saturated concentrations of
dioxygen in KOH solutions

D Zhang, J F Wu, L Q Mao, T Okajima, F Kitamura , T Ohsaka* & T Sotomura

 

Hydrodynamic chronocoulometry has been applied to determine diffusion coefficients and saturated concentrations of dioxygen in 0.1 to 15 M potassium hydroxide solutions. The values of diffusion coefficient and saturated concentration of dioxygen decrease with increasing concentration and kinematic viscosity of KOH solutions. Furthermore various physicochemical quantities of KOH solutions have been estimated at 25.5°C. The product of diffusion coefficient of dioxygen and viscosity of KOH solution shows a constant value, i.e., (1.4 ± 0.3) × 10-7 g cm s-2, within the experimental error for 1 to 8 M KOH solutions. The conductivity of KOH solutions show a quartic relation with respect to KOH concentration, and its highest value is obtained at the 8 M KOH solution.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 807-812

 

 

Dynamics of the influence of redox active conducting polymer
on corroding interface

S Shriram, S Karthikeyan, S Pitchumani* & N G Renganathan

 

A study of Al/Al2O3/polyaniline interface in a corrosive medium, using which an equivalent circuit model has been evolved, based on electroanalytical measurements, has been reported. The model evolved has been used to simulate interfacial parameters such as Cdl, Rct, Q, Rs for different experimental conditions, and these have been used to diagonise the nature and type of protective role the polyaniline coating offers. Synergization of experimentally observed parameters and simulated parameters from equivalent circuit models has been demonstrated as a protocol to evaluate the protective nature of polyaniline coating.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 813-818

 

 

Mercury selective electrochemical sensor based on
a double armed crown ether as ionophore

Vinod K Gupta*, Sudeshna Chandra & Shiva Agarwal

 

PVC based membranes of a double armed crown ether, N, N’-dibenzyl, 1,4,10,13-tetraoxa-7, 16-diaza cyclooctadecane (I) as ionophore with sodium tetra phenyl borate (NaTPB) as anion excluder and with many plasticizing solvent mediators have been prepared and used for Hg(II) ion determination. The membrane with DBBP (dibutyl butyl phosphonate ) as plasticizer with various ingredients in the ratio PVC: I: NaTPB: DBBP (150: 12: 2: 100) shows the best results in terms of working concentration range (3.1×10-5-1.0 ×10-1M) with a Nernstian slope (29.0± 0.5 mV/decade of activity). The electrode works in the pH range 2.1-4.5. The response time of the sensor is 15s and it can be used for about 4 months in aqueous as well as in non-aqueous medium. It has good stability and reproducibility. The potentiometric selectivity coefficient values for mono-, di-, and trivalent cations are tabulated. The sensor is highly selective for Hg2+ in the presence of normal interferents like cadmium, silver, sodium and iron.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 819-823

 

 

Pb(II) sensor based on the membrane of 3,4,4a,5-tetrahydro-3-methylpyrimido-[1,6-a] benzimidazole-1 (2H) thione in PVC matrix

A K Jain*, S M Sondhi & Shefali Rajvanshi

 

3,4,4a,5-Tetrahydro-3-methylpyrimido [1,6-a] benzimidazole-1 (2H) thione (TMPB) has been synthesized and investigated as electroactive phase of membranes for use as Pb2+ selective electrode. PVC based membranes of TMPB have been prepared without plasticizer and with a number of plasticizers and investigated. Of the various plasticizers used, tris (2-ethylhexyl)phosphate (TEP) has been found to improve the performance of the membrane significantly. The membrane having the composition of TMPB:PVC:TEP as 1:40:10 has been found to perform best . The electrode having such a membrane responds linearly to Pb2+ over a wide concentration range, 1.9´10-5-1.0´10-1M, with a slope of 28.5 mV/decade of concentration and small response time of 20 s. The electrode can work over a pH range of 2 to 5.7 and also in partially non-aqueous media. Selectivity coefficient values revealed that the electrode is sufficiently selective over a large number of mono, bi- and trivalent metal cations. It is found to have a life time of one month and could also be used as indicator electrode in the potentiometric titration of Pb2+ with EDTA.

 

 

   

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 824-829

 

 

Electrooxidation of physostigmine at different electrodes

Bengi Uslu*, İnci Biryol, Melike Kabasakaloğlu & M Levent Aksu

 

The electrooxidation of physostigmine (PHY) has been investigated at different pH values at platinum, ruthenium, carbon paste and glassy carbon electrodes. It has been found that Ru and Pt electrodes played an important role in the oxidation. The nature of the curves are strongly dependent upon the scan rate, supporting electrolyte and the pH values of the solutions. With glassy carbon electrode, the results are highly dependent upon the activation process of the electrode. Activated glassy carbon and oxidized Pt and Ru electrodes give the best results. Suitable mechanisms for oxidation of PHY in both acidic and basic media have been proposed.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 830-835

 

 

Polarographic and voltammetric reduction of some
pyrazoline-5-ones in aqueous and micellar media

Wahid U Malik*a & M Joseph

 

Polarographic and voltammetric reduction of several benzylsulphonyl pyrazolines have been studied. The reduction is found to occur at the exocyclic hydrazono group. The effect of surfactants, ionic strength, cations and anions and solvent composition has been studied. The effect of substituents has been evaluated and a tentative mechanism for the reduction of hydrazono group in micellar medium is presented.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 836-838

 

 

Autopolymerization of pyrrole on the silver substrates roughened by an electrochemical method

Yu-Chuan Liu* & Shung-Jim Yang

 

Silver substrates have been roughened by a triangular-wave oxidation-reduction cycle (ORC) for 10 scans in an aqueous solution containing 0.1 N KCl The AgCl4- complexes with grain sizes smaller than 100 nm are formed on the roughened Ag substrates. The pyrrole (Py) monomers are found to be autopolymerized on the roughened Ag substrates due to the electrochemical activity of the complexes. The polymerized polypyrrole (PPy) film has been confirmed by the characteristic bipolaron bands at ca 923 and 1203 cm-1 shown in the FTIR spectrum.

 

 

    

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 839-842

 

 

Voltammetric determination of thallium(I) on a prussian
blue/cinder paste electrode

Jyh-Myng Zen*, Hsing Ho & Pei-Yan Chen

 

The effective utilization of industrially waste cinder for electroanalytical applications by trapping the hexacyanometallate (HCF) units from Fe3+, Ni2+, Co3+, etc into the interlayer galleries of cinder has been reported. Prussian blue (PB) is an Fe(III)-HCF with mixed valence and zeolite type properties. In the present investigation, the intercalation property of Tl+ with PB/cinder paste electrode (designated as PBCPE) has been utilized for the analytical purpose. Basic cyclic voltammetric experiments with Tl+ in 0.1 M KNO3 results in a continuous insertion of Tl+ ions inside the PB gallery with the ejection of K+ ions. The insertion rate of Tl+ ions in the PBCPE was much faster as compared to that in traditional PB-modified electrodes. The PBCPE has alse been utilized for sensitive determination of Tl+ ions in real samples.

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 843-846

 

 

Use of voltammetric methods for the analysis of
trace metals in engine oils

P K Tamrakar & K S Pitre*

 

Accurate and convenient analytical procedures have been developed for the trace determination of metal ions in unused engine oil using advanced voltammetric methods viz. direct current polarography (DCP), differential pulse polarography (DPP) and differential pulse anodic stripping voltammetry (DPASV). The analysis has been carried out after ashing the samples and converting it to aqueous solution. Trace metals have been determined at different pH values in 0.1M (NH4)2 tartrate, 0.1M KCl and 0.01M EDTA as supporting electrolyte with 0.001% gelatin as a maximum suppressor. The results reveal that Cr, Pb, Cd, Zn, Co, Fe and Cu are present in the sample in significant amounts. The observed voltammetric results have been compared with those obtained using AAS. Statistical treatment of the observed voltammetric data reveal high accuracy and good precision of determination.

 

 

 

 

Indian Journal of Chemistry

Vol. 42A, April 2003, pp. 847-848

 

 

SEQ CHAPTER \h \r 1Electrochemical proof of the single bond character of the N-N bonds in some 1,2,4-triazines

J Ludvik & P Zuman*

 

Whereas in molecules containing grouping X=C-C=Y (X, Y = C, 0, N, S) delocalization of electrons takes place, in compounds containing the grouping C=N-N=C the central N-N bond has a single bond character and conjugation does not play a role. The single bond character of the N(1)-N(2) bond in 1,2,4-triazin-5-ones has been confirmed based on identity of reduction potential of the 1,6-azomethine bond in the parent compound and of the 1,6-C=N bond in the corresponding 2,3-dihydroderivative. Lack of delocalization has also been proved for acyclic azines. Comparison of half-wave or peak potentials is a simple and efficient way to prove or disprove the role of the delocalization of electrons over the studied molecule.