Showing papers on "Polarography published in 2000"

The voltammetric study and determination of ramipril in dosage forms and biological fluids.

Abstract: The voltammetric behavior of ramipril was studied using cyclic voltammetry, direct current polarography (DC t ), differential pulse polarography (DPP) and alternating current polarography (AC t ). Ramipril developed well-defined cathodic waves in Britton–Robinson buffers over the pH range 6–12. The waves were characterized as being diffusion-controlled, irreversible and partially affected by adsorption phenomenon. The diffusion–current constant ( I d ) was 1.24±0.02. The current–concentration plots were rectilinear over the range 10–50, 4–40 and 0.16–12 μg/ml in the DC t , DPP and AC t modes, respectively, with a minimum detectability ( S / N =2) of 0.02 μg/ml (4.8×10 −8 M) using the latter mode. The proposed method was successfully applied to the determination of ramipril in commercial tablets. Hydrochlorothiazide, which is frequently co-formulated with ramipril, did not interfere with the assay. Furthermore, the proposed method was applied to the determination of ramipril in urine and plasma adopting the AC t technique. The percentage recoveries were 97.12±0.56 and 94.97±0.62%, respectively. A pathway for the electrode reaction was proposed.

Analysis of heavy-metal-ions using mercury microelectrodes and a solid-state reference electrode fabricated on a Si wafer

Abstract: We have fabricated micro working electrodes and a reference electrode using semiconductor processes for electrochemical detection of heavy-metal-ions. The stripping voltammetry using mercury electrodes has been used to detect trace concentration of ions. If the applied potential to the mercury electrode is negative than the standard redox potentials of heavy-metal-ions, then the ions existing in liquid are amalgamated into the mercury electrode. After this preconcentration process for a few minutes, the potential is increased linearly in the apposite direction and the amalgamated metals are stripped out into solution. By measuring the current peaks while sweeping the voltage, we can find heavy-metal-ions and their concentrations dissolved in the liquid.

The Use of Controlled Potential Electrolysis with a Dropping Mercury Electrode in Elucidation of Organic Electroreduction Mechanisms

Abstract: Controlled potential electrolysis with the dropping mercury electrode, in which a small volume (typically 0.5 to 1.0 mL) of the electrolyzed solution is stirred by the falling off drops, enables coulometric and mechanistic studies unaffected by products formed at the electrode surface. Such electrodes allow establishment of equipotential conditions over the whole electrode surface. Electrolysis is practically complete within 8 to 12 h. When electrolysis products or stable intermediates are electroactive, recording of current–voltage curves during the electrolysis allows detection and following of relatively slow chemical reactions (with half-lives of the order of tens of minutes) which might affect results of preparative electrolyses and would otherwise remained undetected. Reactions of electrogenerated species with limited lifetimes can be followed in this way which would be difficult to detect and follow by other techniques.

Current status of polarography and voltammetry in analytical chemistry

Abstract: Even in the age of separations and atomic absorption electroanalytical methods can be methods of choice in some special cases. To decide when polarography with a dropping mercury electrode or voltammetry with other types of electrodes can be successfully used, limitations and advantages of analytical applications of these techniques are summarized. Examples of recent application to some basic problems (lack of conjugation in C=N-N=C groupings, acid-base and hydration-dehydration reactions) and applied problems (analyses of heterogeneous suspensions used in investigation of Me2+ with bile salts, adsorption of pesticides on lignin, alkaline cleavage of lignin under mild conditions) are given.

Electrochemical Reduction of Cefepime at the Mercury Electrode

Abstract: The differential pulse polarography, DC-tast polarography and cyclic voltammetry behavior of cefepime was studied in phosphate buffer solutions (pH 1.6–12.1). In acidic media, a non reversible diffusion controlled reduction process involving two electrons takes place. The reduction mechanism is discussed. The linear relationship between peak current intensity and cefepime concentration allowed the differential pulse polarographic determination of cefepime over a wide concentration range, from 10–6 to 10–4 M at pH 2.7, with a relative standard deviation of 1.7% (eleven determinations at the 4×10–5 M level). The described procedure has been applied to determination of the drug in pharmaceutical formulations and human urine samples.

Interaction between Monoaza-, Diaza-, or Polyazacrown Ethers and Alkali Metal Ions in Acetonitrile by Polarography

Abstract: The complex formation constants between alkali metal ions and monoaza- or diazacrown ethers (L) in acetonitrile have been obtained by the analytical method of d.c. polarography, in which a positive shift in E1/2 of the mercury-dissolution wave of L in the presence of a large excess of M+ is utilized. By the conventional method using a negative potential shift of the reduction of ML+ in the presence of a large excess of L, similar values of the complex formation constants were given for the 1:1 interaction (ML+ formation) between M+ and L. Concerning the stability of the Li+ and Na+ complexs of 12-crown-4, 15-crown-5, and 18-crown-6, the effects of the NH groups in the crown ethers have been discussed. The interaction between alkaline earth metal ions and L was too strong to obtain the formation constant, except for the BaL2+ species of 1-aza-12-crown-4. The anodic processes of L on DME were clarified: the diaza-12-crown-4 as well as the monoazacrown ethers caused an anodic wave of one-electron for L (i.e., the formation of 1/2[HgL2]2+), whereas 1,7-diaza-15-crown-5 gave successive two anodic waves. The formation of the monomeric mercurous ion (Hg+) seemed to be stabilized by the diaza-15-crown-5 in the course of the anodic process into [HgL]2+.

The Source of the Anomalous Cathodic Peak During ASV with In Situ Mercury Film Formation in Chloride Solutions

Abstract: In situ mercury film depositions at a glassy carbon electrode at various concentrations of sodium chloride or hydrochloric acid were performed. In the chloride concentration range of 0.001 to 0.5 M, an anomalous cathodic peak is observed during the anodic scan when performing square wave voltammetry. This phenomenon has previously been attributed to the formation of mercury(I) chloride (calomel) on the electrode surface. Cyclic voltammetry indicated that electrochemically generated calomel, which forms due to the oxidation of the mercury film in solutions with greater than 0.00 1 M Cl ˇ , is reversible and is reduced to elemental mercury during cathodic polarization of the electrode. It is proposed that the cathodic peak is a result of the calomel which forms after Hg(O) is oxidized to Hg(I) by Hg(II) ions and subsequent reaction of Hg(I) with chloride ions. This insoluble nonelectrochemically generated calomel is formed under open circuit conditions and, not being reduced during the cathodic polarization, is reduced at more anodic potentials. The most stable and reproducible responses of this system for ASV of Cd 2a and Pb 2a is obtained when the mercury is removed from the electrode surface by electrochemical oxidation at the end of each anodic scan.

Determination of trace elemental sulfur and hydrogen sulfide in petroleum and its distillates by preliminary extraction with voltammetric detection

Abstract: Determination of elemental sulfur and hydrogen sulfide at sub-ppm levels in petroleum and its distillates was individually investigated using two convenient, accurate and sensitive procedures. These involved preliminary extraction of sample species, which were then detected by differential pulse polarography (DPP) and square wave voltammetry (SWV) on dropping mercury and static mercury drop electrodes, respectively. In one procedure, the required amount of sample was diluted with isopropyl alcohol–toluene (2 + 1 v/v) and was heated to 80 °C. Hydrogen sulfide available in the sample was then delivered through a designed system to an absorber cell by a controlled flow of helium gas in order for its concentration to be determined by SWV detection. In another procedure, an appropriate amount of sample was shaken with a recommended volume of extraction solution. The mixture was filtered in two steps and was then ready for its elemental sulfur content to be measured by DPP detection. The effects of extraction parameters such as volume ratio of extraction solution to sample, type of extraction solution and extraction time were studied in order to achieve a high recovery of sulfur. Various instrumental factors such as scan rate, pulse height, initial and final potential and purge time were optimized. The method was free from interferences from organic sulfides, disulfides and thiophene. The 3ς detection limits were 10 and 100 ng g−1 for H2S (by use of SWV) and S0 (by use of DPP), respectively. At a 1 μg g−1 level in samples, the relative standard deviations (n = 4) were 1.7 and 3.3% for SWV and DPP, respectively

Study of Complex Formation Between 18-Crown-6 and Pb2+, Tl+ and Cd2+ Cations in Binary Aqueous/Non-aqueous Solvents Using Polarographic Techniques (DPP and SWP)

Abstract: The complexation of Pb2+, Tl+ and Cd2+ cationsby 18-crown-6 was studied in water/propanol (H2O/PrOH),water/acetonitrile (H2O/AN) and water/dimethylformamide(H2O/DMF) binary systems at 20 °C using squarewave polarography (SWP) and differential pulse polarography (DPP).It was confirmed that the stoichiometry of each of the complexes formed between 18C6 and the respective cations is 1 : 1. The formation constants of the complexes were found to increase with increasing concentration of the non-aqueous solvent. In all cases, a stability order of Pb2+ > Tl+ > Cd2+ was observed. In general,the stabilities of individual complexes were found to decrease as the binary solvent mixture varied from H2O/AN to H2O/PrOH to H2O/DMF.

Electrochemical study of cefetamet-Na and its polarographic determination.

Abstract: Polarographic behavior of cephalosporin cefetamet–Na (Cef–Na) in aqueous solutions of pH ranging from 1.7 to 12.5 was investigated by applying direct current (dc) polarography, differential pulse polarography (dpp), alternating current (ac) polarography, cyclic voltammetry and electrolysis at constant potential. The characteristics of the corresponding electrode reaction are presented and discussed. The electrode reaction was found to be affected by strong adsorption, strongly and slightly pronounced in acidic and alkaline media, respectively. The methoxyimino group electroreduction was carried out and the mechanistic scheme was suggested. In addition, a sensitive dpp method was proposed for analytical determination of a very low concentrations of Cef–Na.

Electrochemical determination of rate constants and product yields for the spontaneous dediazoniation ofp-nitrobenzenediazonium tetrafluoroborate in acidic aqueous solution

Abstract: We have examined the kinetics and mechanisms of the dediazoniation of p-nitrobenzenediazonium tetrafluoroborate in acidic aqueous solutions by employing differential pulse polarography (DPP) and differential pulse voltammetry (DPV) on a glassy carbon electrode combined with the use of a coupling reaction to quench unreacted p-nitrobenzenediazonium ion. These electrochemical techniques show an effective sensitivity and selectivity for detecting arenediazonium ions and arenedediazoniation products under the appropriate experimental conditions (pH, solvent, electrolyte), which allows simultaneous monitoring of the rates of arenediazonium ion loss and product formation and determination of product yields. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 419–430, 2000

Polarographic Behavior and Determination of Pendimethalin in Formulations, and Environmental Samples

Abstract: A differential pulse polarographic (DPP) method for the determination of pendimethalin is described based on the reduction of a nitro group at a dropping mercury electrode in BR buffers of pH 2.0 to 12.0 using 25% acetone-water mixtures as a solvent. Also, a cyclic voltammetry (CV) technique has been used to study the behavior of pendimethalin at a hanging mercury drop electrode. The differential pulse polarographic method described here has been applied to the determination of pendimethalin in formulations, grains, soils and spiked water samples. Both standard addition and calibration methods were used for the analytical measurements. The lower detection limit was found to be 1.87 × 10-8 M (M = mol dm-3).

Adsorption and Reduction of Berberine at a Mercury Electrode

Abstract: Adsorption and reduction of berberine are investigated by alternating current polarography and square-wave voltammetry in electrolytes of various pH. Both berberine and the product of its reduction canadine form condensed films on the mercury electrode surface. These processes limit the analytical application of square-wave voltammetry combined with adsorptive accumulation of berberine. Reduction of berberine is totally irreversible and occurs between - 0.95 V and - 1.35 V, depending on berberine concentration and pH of solution. Canadine is electroinactive and can not be reoxidized on mercury electrode. Its condensed film is very stable, even at - 0.5 V, and may prevent adsorption of berberine. The properties of square-wave voltammetric responses of berberine in acidic, neutral and basic electrolytes are reported and the conditions for their electroanalytical application are discussed.

Electroreduction of Nitroaryl‐1,4‐dihydropyridines on a Mercury Pool Electrode in Mixed Media Analysis of the Reaction Products and Their Reactivity with Biomolecules

Abstract: The electroreduction of a series of nitroaryl-1,4-dihydropyridines has been studied in mixed media. Controlled potential electrolyses using a mercury pool electrode at three different reduction potentials were carried out. Voltammetric (polarography and cyclic voltammetry) and chromatographic studies, showed that these nitro compounds were transformed into their corresponding hydroxylamine derivatives at the end of the electrolysis. On the other hand, early in the electrolysis it was possible to detect the formation of the nitro radical anion in the bulk solution which through a dismutation reaction produces the nitroso compound which is reduced to the final product, a hydroxylamine derivative. When different biomolecules like glutathione, cysteamine, adenine, and uracil were added, a direct reaction with the nitro radical anion derivative was detected. The parent nitro compound and the final product, the hydroxylamine derivative, did not react with the biomolecules.

Stoichiometry and Stability of Complexes Formed between 18-Crown-6 as well as Digenzo-18-Crown-6 Ligands and a Few Metal Ions in Some Non-aqueous Binary Systems Using Square Wave Polarography

Abstract: The complexation reaction between Pb2+,TI and Cd2+ions and macrocyclic ligands, 18-crown-6 ( 18C6) and dibenzo- 18-crown-6 (DB 18C6), was studied in dimethylsulfoxide (DMSO)-nitromethane (NM) and dimethyl-formamide (DMF)-nitromethane binary system s by square wave polarography (SWP) technique. The stoichiometry and stability of the complexes were determined by monitoring the shifts in half-waves or peak potentials of the polarographic waves of metal ions against the Iigand concentration. In most cases, the stability constants of complexes increase with increasing amounts of the nitromethane in mixed binary solvents used in this study. The complexes formed between 18C6 and DB18C6 and these metal cations in all cases had a stoichiometry of 1 : 1. The results obtained show that there is an inverse relationship between the formation constant of complexes and the donor number of solvents based on a Gatmann donocity scale and the stability constants show a high sensitivity to the composition of the mixed solvent systems. A linear behavior was observed for variation of log Kf of I8C6 complexes vs the composition of the mixed solvent systems in NM/DMSO and NM/DMF,but a non-linear behavior was observed in the case of DB 18C6 complexes in these binary systems. In most of the systems investigated, the Pb2+ cation forms a more stable complex with the 18C6 than other two cations and the order of selectivity of this Iigand for cations is: Pb2+ > TI+,Cd2+.

Electrochemical Behavior of Benzo[c]cinnoline-N-oxide at Mercury Electrode

Abstract: Electrochemical behavior of benzo[c]cinnoline-N-oxide was studied. Two discrete 2 and 4 electron reduction waves in acidic media but only one wave in basic media were observed in ethanol-BR buffer system (1:5 v/v). The number of electrons transferred and the difussion coefficient were determined by using various voltammetric techniques, such as sampled current polarography, cyclic voltammetry, chronoamperometry, chronocoulometry and constant potential coulometry. Adsorption of the molecule on the surface of the mercury drop was analyzed and this phenomenon was exploited to calculate the diffusion coeffcient of benzo[c]cinnoline-N-oxide. A mechanism for the electrode reaction is proposed.

Voltammetric behaviour of clonixin and its differential pulse polarographic determination in tablets

Abstract: Clonixin, a non-steroid analgesic, can be both reduced at the mercury electrode and oxidised at the glassy carbon electrode. The anodic response shows well-defined waves in a pH range between pH 2-12. The polarographic response shows two irreversible waves or peaks in the range between pH 1-6 shifting cathodically when pH increases. Above pH 7.0 all the signals disappeared. The first signal in the dpp mode at pH 1.8 was selected for analytical use. The polarographic

An electrochemical approach to the determination of dinobuton: a study of water samples

Abstract: The electrochemical reduction behaviour of dinobuton was studied by employing advanced electrochemical techniques such as dc polarography, cyclic voltammetry, differential pulse polarography (DPP), controlled potential electrolysis and millicoulometry in universal buffers of pH ranging from 2.0 to 12.0. Polarographic and cyclic voltammetric studies of dinobuton showed that it is reduced in two six-electron steps in acidic medium and in two four-electron steps in basic medium. Polarographic waves are irreversible and diffusion controlled in nature and are precisely proportional to the concentration of dinobuton. A reduction mechanism is proposed on the basis of voltammetric results and reduction product analysis. The dependence of the DPP peak on various parameters was studied and the optimum conditions for the determination of dinobuton were found. Finally, the developed DPP method was applied to the determination of dinobuton in agricultural formulations and in spiked water samples. Evaluation by the standard addition method confirmed the accuracy of the analytical procedure.