Showing papers on "Polarography published in 2012"

Fluorescence and Electrochemical Sensing of Pesticides Methomyl, Aldicarb and Prometryne by the Luminescent Europium-3-Carboxycoumarin Probe

Abstract: This work describes the application of time resolved fluorescence in microtiterplates and electrochemical methods on glassy carbon electrode for investigating the interactions of europium-3-carboxycoumarin with pesticides aldicarb, methomyl and prometryne. Stern-volmer studies at different temperatures indicate that static quenching dominates for methomyl, aldicarb and prometryne. By using Lineweaver-Burk equation binding constants were determined at 303 K, 308 K and 313 K. A thermodynamic analysis showed that the reaction is spontaneous with ΔG being negative. The enthalpy ΔH and the entropy ΔS of reactions were all determined. A time-resolved (gated) luminescence-based method for determination of pesticides in microtiterplate format using the long-lived europium-3-carboxycoumarin has been developed. The limit of detection is 4.80, 5.06 and 8.01 μmol L−1 for methomyl, prometryne and aldicarb, respectively. This is the lowest limit of detection achieved so far for luminescent lanthanide-based probes for pesticides. The interaction of the probe with the pesticides has been investigated using cyclic voltammetry (CV), differential pulse polarography (DPP), square wave voltammetry (SWV) and linear sweep voltammetry (LSV) on a glassy carbon electrode in I = 0.1 mol L−1 p-toluenesulfonate at 25 °C. The diffusion coefficients of the reduced species are calculated. The main properties of the electrode reaction occurring in a finite diffusion space are the quasireversible maximum and the splitting of the net SWV peak for Eu(III) ions in the ternary complex formed . It was observed that the increase of the cathodic peak currents using LSV is linear with the increase of pesticides concentration in the range 5 × 10−7 to 1 × 10−5 mol L−1. The detection limit (DL) were about 1.01, 2.23 and 1.89 μmolL−1 for aldicarb, methomyl and prometryne, respectively. In order to assess the analytical applicability of the method, the influence of various potentially interfering species was examined. Influence of interfering species on the recovery of 10 μmol L−1 pesticides has been investigated.

Differential pulse polarographic investigation of the antifungal drugs itraconazole, ketoconazole, fluconazole and voriconazole using a dropping mercury electrode.

Abstract: The electrochemical reactions of the antifungal drugs itraconazole, ketoconazole, fluconazole and voriconazole have been investigated by differential pulse polarography (DPP) using a dropping mercury electrode (DME). All investigations were carried out in Britton-Robinson buffer solutions and methanol with varying pH values. Ketoconazole and itraconazole both showed a reduction peak with a potential between -1.5V and -1.6 V. Stable and reproducible conditions for the determination of itraconazole (c = 1 x 10(-7) M) were found within the pH range of 6.0 to 8.0 and for the determination of ketoconazole (c = 5 x 10(-8) M) within pH 6.0 to 7.0. Voriconazole showed a reduction peak with a peak potential of -1.7 V (c = 1 x 10(-5) M) within the pH range of 8.0 to 10.0. In the case of fluconazole no electrochemical activity was found.

New Luminescent Bioprobes Eu(lll)-phloroglucinol Derivatives and Their Spectrofluorimetric, Electrochemical Interactions with Nucleotides and DNA

Abstract: Two new ligands derived from phloroglucinol 2-{[(4-methoxy benzoyl ) oxy ] } methyl benzoic acid[L1] and 2-{[(4-methyl benzoyl )oxy] methyl} benzoic acid[L2] were synthesized. The solid complex Eu(III)-L2 has been synthesised and characterized by elemental analysis ,UV and IR spectra. The reaction of Eu(III) with the two synthesized ligands has been investigated in I = 0.1 mol dm-3 p-toluene sulfonate by cyclic voltammetry and square wave voltammetry. The reaction of Eu (III)–L1 and Eu (III)–L2 binary complexes with nucleotide 5′-AMP , 5′-ADP ,5′-ATP , 5′- GMP , 5′-IMP , and 5′-CMP has been investigated using UV, fluorescence and electrochemical methods. The experimental conditions were selected such that self-association of the nucleotides and their complexes was negligibly small, that is, the monomeric complexes were studied. The interaction of the Eu(III)–L1 or L 2 solid complexes with calf-thymus DNA has been investigated by fluorescence and electrochemical methods including cyclic voltammetery(CV) ,differential pulse polarography (DPP) and square wave voltammetry (SWV) on a glassy carbon electrode. The fluorescence intensity of Eu(III)-L2 complex was enhanced with the addition of DNA. Under optimal conditions in phosphate buffer pH 7.0 at 25 °C the linear range is 3–20 μM for calf thymus DNA (CT–DNA) and the corresponding determination limit is 1.8 μM.

Combination of chemometrically assisted voltammetry, calorimetry, and circular dichroism as a new method for the study of bioinorganic substances: application to selenocystine metal complexes.

Abstract: Selenium-containing compounds play an important role in antioxidant defense systems, binding to toxic metals, preventing their uptake into cells, and thus protecting cells from metal-induced formation of reactive oxygen species. Here, we present a proposal for a relatively new method as a complement to the more usual methods used in selenium studies. A systematic study of the metal-binding properties of selenocystine (SeCyst) in the presence of divalent metal cations (Cd, Co, Hg, Ni, and Zn) is reported. Isothermal titration calorimetry provides thermodynamic parameters of the systems. Titrations produced curves that could be fit reasonably well to the one set of sites model. The data clearly demonstrate that one M2+ binds one SeCyst molecule, and the stable M(SeCyst) complex is formed under these conditions. The order of the SeCyst binding constant for the metal ions is Hg2+ > Cd2+ ~ Zn2+ > Ni2+> Co2+. Cadmium ion was selected as a modulator for the behavior of SeCyst in the presence of a nonessential metal, and zinc was selected for the case of an essential element. These interactions of SeCyst with Cd2+ and Zn2+, either individually or combined, were studied in aqueous buffered solutions at physiological pH by differential pulse polarography and circular dichroism spectroscopy. Furthermore, recently developed chemometric tools were applied to differential pulse polarography data obtained in mixtures of SeCyst and glutathione in the presence of Cd2+ at physiological pH.

Investigation of Electrochemical Behavior of 2-(5-Bromo-2-Pyridylazo)-5-[N-Propyl-N-(3-Sulfopropyl)Amino] Phenol Disodium Salt Dihydrate

Abstract: The voltammetric and polarographic behavior of 2-(5-bromo-2-pyridylazo)-5-[N-propyl-N-(3-sulfopropyl)amino]phenol disodiumsalt dihydrate (5-Br-PAPS) at a hanging mercury drop electrode (HMDE) and static mercury drop electrode (SMDE) has beenstudied by several techniques including square-wave voltammetry (SWV), differential pulse polarography (DPP), direct currentpolarography (DCP) and cyclic voltammetry (CV). Current-potential curves recorded at a HMDE and SMDE provide informationabout the electrode reaction mechanism. The electrochemical reduction mechanism of the azo compound is suggested using SWV,DPP, DCP and CV techniques in different electrolyte media.© 2012 The Electrochemical Society. [DOI: 10.1149/2.031210jes] All rights reserved.Manuscript submitted February 14, 2012; revised manuscript received July 6, 2012. Published August 29, 2012.

Polarographic reduction of curcumin at dropping mercury electrode

Abstract: The polarographic reduction of curcumin has been done in various conditions, at different temperatures, at different solvent and at different concentrations by D. C. Polarography. The electrode processes were irreversible and exhibit diffusion controlled reduction. Single well defined irreversible wave obtained. The polarographic technique was used to determine the kinetic parameters (K 0 fh , αn) and thermodynamic parameters such as enthalpy change (ΔH), free energy change (ΔG) and entropy change (ΔS) of curcumin at pH-6 in 0.5M acetate buffer. Keyword : Curcumin, D.C. Polarography, Kinetic parameters, Thermodynamic parameters.

Electrochemical Behavior of Quinoxalin-2-one Derivatives at Mercury Electrodes and Its Analytical Use

Abstract: Derivatives of quinoxalin-2-one are interesting compounds with potential pharmacological activity. From this point of view, understanding of their electrochemical behavior is of great importance. In the present paper, a mechanism of electrochemical reduction of quinoxalin-2-one derivatives at mercury dropping electrode was proposed. Pyrazine ring was found to be the main electroactive center undergoing a pH-dependent two-electron reduction process. The molecule protonization of nitrogen in the position 4 precedes the electron acceptance forming a semiquinone radical intermediate which is relatively stable in acidic solutions. Its further reduction is manifested by separated current signal. A positive mesomeric effect of the nonprotonized amino group in the position 7 of the derivative III accelerates the semiquinone reduction yielding a single current wave. The suggested reaction mechanism was verified by means of direct current polarography, differential pulse, cyclic and elimination voltammetry, and coulometry with subsequent GC/MS analysis. The understanding of the mechanism was applied in developing of analytical method for the determination of the studied compounds.

Application of different chemometric strategies to voltammetric and UV-vis spectroscopic data to obtain a complexation model: study of the Cu(II) binding with the phytohormone 6-benzylaminopurine.

Abstract: The complexation processes of Cu(II) by the phytohormone and the possible antitumoral agent 6-benzylaminopurine (BAP) were studied by Differential Pulse Polarography (DPP) and ultraviolet-visible spectroscopy (UV-vis) in combination with chemometric programs such as Multivariate Curve Resolution by Alternating Least-Squares (MCR-ALS) and Gaussian Peak Adjustment (GPA). All data confirm the formation of the predominant 1:1 and 1:2 Cu2+:BAP complexes. The corroboration of the presented stoichiometries was performed by ElectroSpray Ionization-Mass Spectrometric (ESI-MS) experiments of the Cu(II)–BAP system at different ratios.

Review of the catalytic voltammetric determination of titanium traces.

Abstract: Catalytic and catalytic adsorptive stripping voltammetry are some of the most sensitive analytical methods. A review of various catalytic and catalytic adsorptive systems of titanium and their use in voltammetric analysis is presented. The mechanisms of catalytic reactions are discussed in detail. In addition to a survey of literature (91 references), catalytic polarographic, voltammetric and catalytic adsorptive stripping voltammetric determination of titanium traces at liquid mercury and metallic films electrodes are discussed briefly. Moreover, the application of the redox systems Ti(IV)/Ti(III) for the indirect determination of voltammetrically inactive oxidizers participating in catalytic reactions (e.g. chlorates) and voltammetrically inactive ligands (e.g. organic acids and thiocyanates) is also presented.

J. Heyrovský, Japan, and Organic Polarography

Abstract: Polarography is an electroanalytical technique based on recording current-voltage curves using a dropping mercury as the working electrode. It can be used for investigations of both reductions and oxidations of inorganic and organic species. Before WWII the developments of this technique linked Prague (in the then Czechoslovakia) with Kyoto (in Japan, where reductions of organic compounds were first observed). After WWII wide use of this technique has developed, so that in the 1950s and 1960 it became the fifth most frequently used analytical technique. More recently the analytical applications were limited to those of heterogeneous solutions and analyses of some drugs. Its applications in physical organic chemistry involve studies of structure-reactivity relationships and applications to investigations of equilibria and kinetics of rapidly or slowly established processes. DOI 10.1002/tcr.201100042

Synthesis and electrochemical behaviour of 3-(4'-(substituted) sulphonamoylphenyl) azomethine indoles

Abstract: This study presents synthesis of 3-[4'-(substituted) sulphonamoylphenyl] azomethine indoles (SPAI) by refluxing indole3-carboxaldehyde with sulfonamide derivatives. Electrochemical behaviour of SPAI was studied in Britton-Robinson (BR) buffer solution (pH 2.5-12.0) at dropping mercury electrode (DME) and glassy carbon electrode (GCE). Cathodic differential pulse polarographic peak was obtained at DME in pH range 2.5-6.5. Cyclic voltammogram exhibited a well defined, irreversible cathodic and anodic peak at GCE. At pH 6.5 and above, reduction peak exhibited a tendency to split into two peaks, indicating that 1H + /2e reduction of 2-[4’-sulphonamoylphenyl]hydrazono-1,3-indanediones occurs in one 1H + and one 2e steps. A product of CPE was characterized by elemental and spectral analyses.

Current Minimum in Differential Pulse Polarography

Abstract: Current minimum, which sometimes appears as a part of the net response in differential pulse polarography (DPP), was studied in systems characterized by a pronounced IR drop or reactant adsorption. Experimental results obtained on a static mercury drop electrode (SMDE) clearly indicate that this effect is highly influenced not only by solution resistance (or intentionally added resistors) and reactant concentration, but also by both timing parameters (drop time, pulse duration) and electrode surface area. Presentation of the net response along with its components, demonstrates that the current minimum originates from the maximum on dc component, minimum on pulse component or both. In practice, DPP minimum, obtained in measurements with a SMDE, can be treated as an additional diagnostic parameter for the recognition of reactant adsorption or poor experimental conditions (i.e. high resistance within electrode system or low conductivity of the electrolyte medium)

Study of electrode kinetics and thermodynamic parameters of antituberculosis drug isoniazid at d.m.e.

Abstract: The polarographic study of Antituberculosis drug Isoniazid was carried out at dropping mercury electrode (DME). Study of the drug included the effect of different pH, different temperature of medium and different concentration of drug. Isoniazid showed two irreversible waves depending upon the pH. In acidic media it showed two waves while in neutral and alkaline media only one wave was observed. The diffusion current (i d) showed a linear dependence with the drug concentration over the range of 2.9×10 -4 – 2.9×10 -3. The reduction of Isoniazid was found to be irreversible so kinetic parameters (K ofh , αn) were evaluated using Meites-Israel and Gaur-Bhargava’s methods. Thermodynamic parameters such as ∆Hp ≠, ∆Hv ≠, ∆G ≠ and ∆S ≠ were also evaluated.

Studies on the Kinetic Parameters of Thallium(I) â 50%Methanol-Water Mixture at DME by Faradaic Impedance Technique

Abstract: In this study the kinetic parameters of the system Thallium(I) – 50%Methanol-Water Mixture have been determined by impedance technique using dropping mercury electrode. DC polarographic studies are basic for the plane polarographic analysis and so the system has been studied by that technique also and the transfer coefficient has been determined from this. For analysis of impedance parameters, simple Randles equivalent circuit was used. The investigation was carried out in three different supporting electrolytes, sodium perchlorate, potassium nitrate and potassium chloride and for four different concentrations of the depolariser. The double layer capacity was obtained by extrapolation method for all the systems. The reactant adsorption was not observed in sodium perchlorate and potassium nitrate but it was confirmed in potassium chloride. In the case of sodium perchlorate and potassium nitrate an intermediate nominal adsorption was observed. The standard rate constant Ksh was determined from the charge transfer resistance, which was determined from impedance plots. In all the systems, the reduction of Thallium (I) proceeds in a reversible manner and the values of Ksh were found to be less than one.

Polarographic determination of Cr (VI) in Environmental samples using Catalytic hydrogen currents

Abstract: A sensitive polarographic method for the determination of Chromium is proposed, based on the catalytic hydrogen wave of Cr (VI) - xanthate complexes in the presence of NH4Cl at mercury electrode. The Cr(VI)-xanthate complexes produce a catalytic hydrogen wave at -1.48 V vs SCE with potassium octyl xanthate (Koxan) and at -1.60 V vs SCE with potassium secondary butyl xanthate (Ksbxan) in NH4Cl-NH4OH medium(pH 9.0 for Koxan and 8.5 for Ksbxan). The peak height is proportional to metal ion concentration. The proposed method is free of interference from other metal ions except for Mo (VI), and is evaluated to micro level Cr (VI) down to 0.2 ppm by the determination of Chromium content in drinking water samples, industrial effluents, tannery waste water and agricultural materials.

Chemistry KEYWORDS :Reduction; Mephedrone; Dropping Mercury Electrode (DME);Differential Pulse Voltammetry. Electrochemical Reduction Behavior Of Mephedrone Drug At A Dropping Mercury Electrode And Its Pharmaceutical Determination In Spiked Human Urine Samples

Abstract: The designer drug 1-(4-methylphenyl)-2-methylaminopropan-1-one (4-methylmethcathinone or mephed- rone) is reported to possess psychostimulant, entactogenic and hallucinogenic effects. From the structural point of view mephedrone drug has keto (-C=O) functional group. In the present paper, we have reported the reduction behavior of mephe- drone was studied on the surface of the dropping mercury electrode (DME) as working electrode in universal buffer of pH range from 2.0 to 12.0 by direct current polarography, differential pulse polarography, cyclic voltammetry and controlled potential electrolysis. Mephedrone showed one reduction peak and the results indicated that the reduction processes of mephedrone is irreversible and was diffusion controlled as evidence from linear plots of id against h1/2. Millicoulometric experiment was performed successfully in estimating the number of electrons and protons involved in the reduction processes and to understand reduction mechanism. Kinetic parameters such as diffusion co-efficient (D) and heterogeneous forward rate constant (Kof, h) are evaluated and reported. Quantita- tive measurements were successful in the concentration range 1.0 × 10-5 to 1.5 × 10-9 M with lower detection limit 1.25 × 10-8 M.

Study of Fe 2+ -Curcumin Complex by Polarogaphy

Abstract: The interaction between Curcumin and Fe 2+ was investigated using direct current polarography. The polarographic technique was used to determine the Kinetic parameter (K 0 fh) and thermodynamic parameters such as enthalpy change (ΔH), free energy change (ΔG) and entropy change (ΔS) of Fe 2+ complexes with Curcumin at pH-6 in 0.1M acetate buffer. The electrode processes were irreversible and diffusion controlled.

Electro Chemical Reduction Behavior and Analysis of Cefdinir in Pharmaceutical formulations and Biological media

Abstract: The electrochemical behavior and determination of Cefdinir were studied by different voltammetric techniques such as d.c.polarography, cyclic voltammetry and differential pulse polarography at dropping mercury electrode. Cefdinir exhibits well defined cathodic waves in an universal buffers over a pH range of 2.0 to 12.0.The azomethine group gets reduced to the saturated amine compound by a four electron processes and the reduction mechanism was proposed. The kinetic parameters like Diffusion coefficient (D), transfer coefficient (αna), and heterogeneous forward rate constant (Kf,h.) were evaluated and reported. DPP was used to estimate the title compound in Pharmaceutical formulations and biological media. The relative standard deviation and correlation coefficient values were found to be 0.489 and 0.65% respectively. The proposed method is simple, less time consuming, accurate and even applied for color / excipient solutions without prior separation.

Temporal Instabilities in Cathodic Processes at Liquid and Solid Electrodes

Abstract: Experimental examples and theoretical models of the oscillatory and mutistable behavior in cathodic processes of various species, studied at both liquid (mercury) and solid electrodes, are described. The following processes with the N-NDR characteristics are analyzed: (1) electroreduction of S2O 8 2− ions on mercury and solid (polycrystalline and single crystal) metal electrodes, under conditions when the Frumkin effect of the electric double layer is (or is not) operating; (2) electroreduction of IO 3 − ions on polycrystalline Ag electrode, considered as an HN-NDR type oscillator due to the existence of an additional current carrier; (3) polarographic reduction of In(III)–SCN− complexes; (4) electroreduction of the Ni(II)–SCN− complexes at mercury electrodes, including novel application of the streaming Hg electrode; (5) electroreduction of the Ni(II)–N 3 − complexes at a streaming mercury electrode, exhibiting rarely reported phenomenon of tristability; (6) polarographic electroreduction of Cu2+ in the presence of adsorbed inhibitor (“the inhibitor oscillator”); (7) electroreduction of H2O2 on metal (Ag, Au, Pt) polycrystalline and single-crystal electrodes, including suggestions for a new type of electrochemical oscillator (coupled NDR, CNDR), extending the classification scheme given in Sect. 3.5; (8) electroreduction of H2O2 on Cu-based and GaAs semiconductor electrodes, indicating the specific role of semiconducting phase played only in the latter case. Experimental and model results include both dc and ac (impedance) characteristics.

90 years of polarography: back to the future.

Abstract: It is my great pleasure to present this special issue to celebrate 90 years of polarography. It is certainly appropriate to mention here that polarography has had a major impact on the development of the entire field of electrochemistry and its application. It is not an overstatement to say that without the discovery of polarography and the developments that followed our understanding of electrochemical mechanisms would be much poorer and, consequently, we might not have been able to develop the fuel cells, batteries, solar cells, etc. that we have now. We invited the top contemporary electrochemists to provide their views on current cutting-edge topics of electrochemistry as well as their views on its historical development in the field. We open this special issue with a historical note by Dr. Michael Heyrovský. Consequently, we have reproduced Jaroslav Heyrovský’s original contribution on polarography from Chem. Listy 1922 (in Czech; with kind permission from the Czech Chemical Society) and the first page of the English version of the same article, which appeared in Philosophical Magazine in 1923 (the publisher’s permission did not allow us to publish the full article). Personal Accounts and a Record Review follow. My personal motivation to help organize this special issue was threefold. i) I realize that in the rush for future developments, many young electrochemists are not aware of the roots of their field. As a tree without deep roots cannot grow to great heights, I feel that for electrochemists to achieve their full potential, knowledge of the history of polarography is a key element. Indeed, we are looking to the future for the investigation of new electrode materials (carbon nanotubes, graphene, etc.), but it is very helpful to look back and realize that at one time, there was a material which had an atomically smooth surface, provided excellent reproducibility of measurements, and was even recyclable: mercury. There is much for current research to learn from the history of polarography. ii) I feel that many electrochemists have not had the opportunity to read the original articles. We were able to obtain and reprint the original article from Chemické Listy 1922 (we gratefully acknowledge permission from the Czech Chemical Society). Even though we put forth our maximum effort to obtain permission to reprint the full English version of this article from Philosophical Magazine 1923 from its publisher, we were not successful. Therefore, we are able to present at least the first page. However, it should be mentioned that these articles are available on the Internet. iii) When reading these articles, it is of great interest to look at not only the scientific content, but also at the historical and personal context. When looking at the affiliation of Jaroslav Heyrovský in the key article published in Philosophical Magazine (1923), one can also notice the position held by Jaroslav Heyrovský at the time of publication: “Assistant Professor” (see below).

Spectral and electrochemical studies of fluvoxamine

Abstract: The spectral and voltammetric behavior of fluvoxamine (1) in aqueous buffers of varied pH is presented. Spectrophotometry, cyclic voltammetry, differential pulse polarography and coulometry were utilized to study its proton and electron transfer characteristics. Relevant thermodynamic and electrochemical data such as charge transfer co- efficient (α na ), heterogeneous forward rate constant (k 0 f,h ), etc, have been evaluated. An excellent electroanalytical assaying of 1 has been developed in differential pulse polarography at pH = 3. Molecular modeling on various acid-base conjugates of 1 and their several conformers has been carried out to arrive at the thermodynamic and conformational issues to correlate to the spectral and electrochemical observations.