Showing papers on "Polarography published in 2002"
TL;DR: The present paper describes a procedure that formaldehyde in air was preconcentrated in a membrane cell and its content was determined by adsorptive polarography, which can be adsorbed at the mercury electrode and yields a sensitive adsorption polarographic wave.
36 citations
TL;DR: In this article, the use of this electrode in differential pulse anodic stripping voltammetry enables the direct determination of lead in natural water samples without the elimination of the presence of surface-active substances or the dissolved oxygen.
Abstract: Silver composite electrode prepared from silver and graphite powder and meth-acrylate resin presents a suitable sensor for the voltammetric measurements. Cathodic polarization of this electrode enables the determination of nitrates, nitrites, organic nitro compounds, and halide ions. The use of this electrode in differential pulse anodic stripping voltammetry enables the direct determination of lead in natural water samples without the elimination of the presence of surface-active substances or the dissolved oxygen. The effect of under potential deposition at the composite electrode differs from that effect produced by metallic silver electrode mainly at low concentrations of the deposited metal.
33 citations
TL;DR: Using differential-pulse voltammetry, the drug yielded a well-defined voltammetric response in Britton-Robinson buffer solution, pH 4.0 at -1.286 V, and the method was successfully applied for the analysis of meloxicam in the tablet dosage form.
32 citations
TL;DR: The sonogel–carbon composite electrode is stable and its response is repeatable, and the electrocatalytic oxidation process of cysteine at this new electrode has been studied by cyclic voltammetry.
Abstract: The behavior of cobalt phthalocyanine complexes incorporated inside an hydrotalcite-like clay (HT) or a sonogel–carbon composite has been investigated in order to develop chemically modified electrodes suitable for use as amperometric detectors. The electrocatalytic oxidation process of cysteine at this new electrode has been studied by cyclic voltammetry. For comparison, the oxidation of cysteine catalyzed by the cobalt phthalocyanine complex as a redox mediator, either dissolved in solution or entrapped inside the HT structure, has been followed by polarography. The sonogel–carbon composite electrode is stable and its response is repeatable. Cysteine oxidation is actually induced by the electrogenerated Co(III) complex, and the relevant anodic peak current varies linearly with cysteine concentration within the range 9.0×10–4 to 1.0×10–2 mol L–1.
28 citations
TL;DR: All benzodiazepines can act as ligands toward copper(II) ions, forming 1:1 and 1:2 complexes with similar stabilities, as well as that of the ligands, under varying experimental conditions.
25 citations
TL;DR: In this article, carbon paste electrodes modified with humic acid extracted from a peat area in the Mogi GuaAu River at Sao Paulo State in Brazil showed high reproducibility and particular stability in solution.
Abstract: Polarography at dropping mercury electrode and infrared spectroscopy were used to confirm the reaction of copper(II) ions with humic acid in solution. Polarography allowed observing the reaction to follow the concentration of the Cu(II) in solution while infrared permitted one to follow the humic acid complexation. Cyclic voltammetry experiments, at stationary carbon paste electrode, showed original properties of humic acid which adsorbs at the surface of carbon paste electrode that becomes appropriate for the preconcentration and identification of Cu(II) species. Although very promising the use of adsorption showed the disadvantage of not being reproducible therefore we developed a new preparation method for the carbon paste electrodes modified with humic acid that allow highly repeatable measurements. Humic acid was dissolved in base solution before mixing it with carbon graphite powder and freeze-drying to lead to a fine powder that allows reproducible batches of electrodes. The modification of carbon paste electrode with two different humic acids revealed that the electrochemical behavior of Cu(II) solutions depends on the nature of the humic material. The effects on the electrochemical behavior of Cu(II) of the solutions pH and the ratio of humic acid in the bulk of the electrode were also examined. Such carbon paste electrodes modified with humic acid extracted from a peat area in the Mogi GuaAu River at Sao Paulo State in Brazil showed high reproducibility and particular stability in solution (pH range of 3.0 to 5.5) entitling them to be very good candidates for analytical purposes.
23 citations
TL;DR: Various parameters, such as the effect of the pH, volume of the aqueous phase, flow rate and the interference of a large number of metal ions and anions on the determination of uranium, have been studied in detail to optimize the conditions for its trace determination in various complex materials.
Abstract: Uranium(VI) is adsorbed as a uranium trifluoroethylxanthate (TFEX)-cetyltrimethylammonium (CTMA) ion-pair complex on microcrystalline naphthalene quantitatively in the pH range 4.2 - 7.0. Without cetyltrimethylammonium as the counter ion, the adsorption is hardly 70%. The metal has been desorbed with HCI and determined with a differential pulse polarograph. Uranium can alternatively be quantitatively adsorbed on TFEX-CTMA-naphthalene adsorbent packed in a column at a flow rate of 1 - 5 ml/min and determined similarly. A well-defined peak has been obtained in this medium at -0.20 V versus a saturated calomel electrode. Cyclic voltammetry, differential pulse polarography and D.C. polarography studies indicate that uranium has been reduced irreversibly under these conditions. The detection limit is 0.30 microg/ml at the minimum instrumental settings (signal-to-noise ratio of 2) (with a preconcentration factor of 10, the detection limit would be 30 ng/ml for uranium when the volume in the cell is 15 ml). However if the volume in the cell is 5 ml, it would have been 10 ng/ml with a preconcentration factor of 30. Linearity is maintained in a concentration range of 0.5 - 19.0 microg/ml (2.1 - 79.83 x 10(-9) M) with a correlation factor of 0.9994 and a relative standard deviation of +/-1.1% (in this case 7.5 microg may be concentrated from 150 ml of the aqueous sample where its concentration is as low as 50 ng/ml). Various parameters, such as the effect of the pH, volume of the aqueous phase, flow rate and the interference of a large number of metal ions and anions on the determination of uranium, have been studied in detail to optimize the conditions for its trace determination in various complex materials, like alloys, coal fly ash, biological, synthetic, and waste-water samples.
22 citations
TL;DR: The voltammetric behavior of trazodone (TRZ) HCl was studied using direct current, differential pulse (DPP) and alternating current (AC(t)) polarography and the proposed method was applied to the determination of TRZ in spiked human urine and plasma adopting the DPP technique.
17 citations
TL;DR: A sensitive method for the quantitative determination of acrivastine was developed based on the reduction of the drug at the dropping mercury electrode and the mechanism for the reduction was suggested and the number of electrons involved in the electrode reduction was established.
17 citations
TL;DR: In this paper, a description of determination of Ni, Co, Sb, and As in a mining aqueous sample with complex chemical composition by differential pulse voltammetry (DPV) at a static mercury drop electrode (SMDE) was made.
Abstract: A description is made of determination of Ni (II), Co (II), Sb (III), and As (V) in a mining aqueous sample with complex chemical composition by differential pulse voltammetry (DPV) at a static mercury drop electrode (SMDE). The analyzed sample contained a high concentration of alkaline earth cations (M2−) and pH buffer, thus direct determination was not possible and M2− had to be eliminated. The content of the species could be determined after this sample treatment. The versatility of the polarographic technique for detecting and quantifying major and minor components in the same sample was demonstrated, despite the near peak potentials of the analyzed species.
14 citations
TL;DR: The electrochemical behavior of 2'-halogeno-N,N-dimethyl-4-aminoazobenzene derivatives was investigated using various polarographic and voltammetric methods and a mechanism for the electrode reaction is proposed.
Abstract: The electrochemical behavior of 2′-halogeno-N,N-dimethyl-4-aminoazobenzene derivatives was investigated using various polarographic and voltammetric methods The peak potentials of these derivatives were observed to shift towards negative values along with an increase in the pH A reduction of the azo linkage took place via two electrons at pH > 4, but four electrons at pH < 4 in aqueous-ethanol mixtures The standard rate constants were determined with (Laviron technique) or without (Nicholson technique) taking the adsorption phenomena into account The diffusion coefficients were calculated from the cyclic voltammetric data using a method developed by Garrido The amount of adsorbed substances and transfer coefficients for the electron transfer were also determined A mechanism for the electrode reaction is proposed These compounds can be quantitatively determined between 1 × 10-5 M and 1 × 10-7 with DPP and CV
TL;DR: In this paper, the differential pulse polarography, DC-tast polarography and cyclic voltammetry behavior of acrivastine was studied in pH 2.7 buffer solutions.
TL;DR: In this paper, a theoretical treatment is presented to predict the kinetic behavior of azithromycin at the surface of hanging mercury drop electrode using cyclic voltammetry and a model is developed to incorporate the occurrence of adsorption of the oxidized and reduced species of Azithimeric acid at surface of mercury drop electrodes.
Abstract: A theoretical treatment is presented to predict the kinetic behaviour of azithromycin at the surface of hanging mercury drop electrode using cyclic voltammetry. A model is developed to incorporate the occurrence of adsorption of the oxidized and reduced species of azithromycin at the surface of mercury drop electrode. An analytical solution was obtained using MATHEMATICA (V-3, Wolfram Research, Inc.) to predict the cyclic voltammetric profiles by calculating the currents resulting after applying variable potentials ranging -1.9 to -1.3 V versus Ag/AgCl. Simulation runs at different initial concentrations of azithromycin and different scan rates showed good agreement with experimental findings. However, this model should be modified to describe a multilayer adsorption with irreversible electrochemical reaction.
TL;DR: In this article, Nitrite and nitrate, two prominent anionic forms of nitrogen have been determined at trace levels in natural waters by differential pulse polarization, achieving a limit of determination of 0.10 µg/ml and 0.003 µg /ml, respectively.
Abstract: Nitrite and nitrate, the two prominent anionic forms of nitrogen have been determined at trace levels in natural waters by differential pulse polarography. Limit of determination of 0.10 µg/ml and 0.003 µg/ml were achieved for nitrate and nitrite, respectively.
TL;DR: A fully validated sensitive procedure based on controlled adsorptive accumulation of the drug onto a HMDE was developed for its direct determination without derivatization and applied successfully for determination of praziquantel in its pharmaceutical formulations and human plasma.
TL;DR: In this article, the movement of the mercury surface and the streaming of solution that accompany the current oscillation in the redox reaction of the O 2 /O 2 - (superoxide ion) couple on a hanging mercury drop electrode (HMDE) have been investigated using a combined system of two laser interferometric techniques.
Abstract: The movement of the mercury electrode surface and the streaming of solution that accompany the current oscillation in the redox reaction of the O 2 /O 2 - (superoxide ion) couple on a hanging mercury drop electrode (HMDE) have been investigated using a combined system of two laser interferometric techniques. That is, the simultaneous observation of both of these phenomena could be carried out. The movement of the mercury electrode surface during the oscillation was observed by the Michelson interferometric technique, and at the same time, the streaming of solution around the electrode was done by the Mach-Zehnder interferometric technique. These observations confirm that the electrochemical oscillatory phenomena of the O 2 /O 2 - redox couple are caused by the streaming phenomena, that is, the movement of a mercury electrode surface and adjoining solution resulting from an inhomogeneous polarization of the electrode.
TL;DR: In this paper, the effect of tetraethylammonium perchlorate on the standard electrode reaction rate constants for the one-electron reduction of Eu(CF 3 SO 3 ) 3 on mercury in dimethylsulfoxide has been measured.
TL;DR: In this paper, the electroreduction of the s-triazine derivative 2,4-diamino-1,3,5-Triazine on mercury electrodes was performed in the acidity range 2.25 M H 2 SO 4 to pH 11.
Abstract: This paper presents polarographic (dc and differential pulse) and voltammetric (linear-sweep cyclic voltammetry) studies of the electroreduction of the s-triazine derivative 2,4-diamino-1,3,5-triazine on mercury electrodes. The studies are performed in the acidity range 2.25 M H 2 SO 4 to pH 11. Above this last pH value no signals were obtained. In both dc DP polarography, two reduction waves/ peaks were observed. The overall process corresponded to a two-electron irreversible reduction. For the first wave, the proposed reduction mechanism consists of the two-electron reduction of the reactant protonated in the heterocyclic N3 nitrogen, with reversible electron transfers. The rate-determining step (rds) is a protonation placed after such transfers. At pH values lower than the protonation pK, the protonation reaction takes place prior to the reduction. For the second wave, the unprotonated reactant is reduced and the rds is a protonation placed between the two reversible one-electron transfers. At high pH values, dissociation of the amino group causes the disappearance of the wave.
TL;DR: Polarographic (direct current, dc, and differential pulse, DP) studies of the electroreduction of the s-triazine derivatives ametryn (2-methylthio-4-ethylamino-6-isopropylamino)-1,3,5-tripazine), dimethametryn(2-methylaminamide-6-(1,2-dimethylpropyl) amino-1, 3, 5-tripazine) and simetryn as discussed by the authors were made in the acidity range from 2.25 M H
TL;DR: The proposed method is simple, precise and it was applied successfully for the determination of the miconazole in pure form and in commercial formulations, showing mean recoveries of 99.7-98.4%.
Abstract: Miconazole is reduced at mercury electrode above pH 6 involving organometallic compound formation, responsible for an anomalous polarographic behavior. The electrodic process presents a large contribution of the adsorption effects. The drug can be determined by cathodic stripping voltammetry from 8.0 × 10 −8 to 1, 5 × 10 −6 mol L −1 in Britton-Robinson buffer pH 8.0, when pre-accumulated for 30 s at an accumulation potential of 0 V. A relative standard deviation of 3.8% was obtained for ten measurements of 1.0 × 10 −7 mol L −1 miconazole in B-R buffer pH 8.0 and a limit detection of 1, 7 × 10 −8 mol L −1 was determined using 60 s of deposition time and scan rate of 100 mV s −1 . The proposed method is simple, precise and it was applied successfully for the determination of the miconazole in pure form and in commercial formulations, showing mean recoveries of 99.7–98.4%.
TL;DR: The azo compounds produce a very sensitive polarographic wave at -0.70 V and the method was used to determine nitrite in sausage and the results agree well with those obtained by spectrophotometry.
Abstract: In an acid medium, nitrite diazotized with p-rosani-line and then coupled with 8-hydroxyquinoline in a weak alkaline medium produces azo compounds. The azo compounds produce a very sensitive polarographic wave at -0.70 V (versus the saturated calomel electrode). The height of the peak is linear with the concentration of nitrite in the range of 5 x 10 -9 to 5 × 10 -7 g/mL. The detection limit is 3 x 10 -9 g/mL. The electrochemical characteristics of the polarographic wave are also discussed. The method was used to determine nitrite in sausage. The results agree well with those obtained by spectrophotometry.
TL;DR: In this article, a highly selective, sensitive, rapid and economic adsorptive stripping voltammetric method has been developed for the determination of ultra trace amount of scandium at a carbon paste electrode (CPE) in the current paper.
Abstract: A highly selective, sensitive, rapid and economic adsorptive stripping voltammetric method has been developed for the determination of ultra trace amount of scandium at a carbon paste electrode (CPE) in the current paper. The Sc(III)−alizarin complexan (ALC) complex is adsorbed at the electrode in a mixed buffer solution (pH 5.4) containing 0.04 M acetate and 0.016 M biphthalate, yielding one peak corresponding to the reduction of ALC in the complex at −0.60 V (vs. SCE). The second-order derivative linear scan voltammograms of the complex are recorded by use of model JP−303 polarographic analyzer from −0.10 to −1.10 V. A linear relationship between the second order derivative peak current and Sc(III) concentration in the range of 1.0 × 10−9 to 6.0 × 10−7 M is observed. The detection limit for Sc(III) is 6.0 × 10−10 M. A relative standard deviation of 4.34% is given for ten determinations of 6.0 × 10−8 M Sc(III). The method has been applied to the determination of the trace Sc(III) in the mineral ...
TL;DR: In this paper, the half-wave potentials of electroreduction of ammonia complexes of Pd(II) and Ni(II), as well as other complexes are investigated.
Abstract: Kinetics and mechanism of electroreduction of complexes Pd(NH3)42+ on a dropping mercury electrode (DME) and a Pd electrode, as well as ammonia complexes of Co(II), Ni(II), and Zn(II) and hydroxyammonia complexes of Zn(II) on DME at different concentrations of ammonia and supporting electrolytes and different pH values are discussed. The half-wave potentials of electroreduction of ammonia complexes of Pd(II) and Ni(II) on DME in the absence of a polarographic maximum obey an equation that takes into account the effect the EDL structure has on the rate of a slow outer-sphere electrochemical stage. As opposed to Pd(II) complexes, the reduction of the other complexes involves preceding reversible chemical stages, which yield diammonia complexes undergoing a direct reduction on DME. The reasons for the emergence of a polarographic maximum upon an increase in the concentration of reduced complexes and the time of recording an instant current are discussed.
TL;DR: In this article, the optimum conditions for sample preparation and electrolysis in detecting the electrochemical peak of nifedipine reduction were found, and a procedure for determining 10 −9 to 5 × 10 −7 M of this preparation by differential pulse stripping polarography at a stationary mercury electrode using accumulation for 5 min was proposed.
Abstract: The optimum conditions for sample preparation and electrolysis in detecting the electrochemical peak of nifedipine reduction were found. A procedure for determining 10–9 to 5 × 10–7 M of this preparation by differential pulse stripping polarography at a stationary mercury electrode using accumulation for 5 min was proposed.
Journal Article•
TL;DR: In this article, the electrochemical reduction of four 4'-halogene-4-aminoazobenzene derivatives was studied in water/ethyl alcohol mixtures at various pH values using cyclic voltammetry (CV), sampled d.c. polarography (SCP), differentialpulse polarography(DPP), chronoamperometry (CA) and constant potential coulometry (BE).
Abstract: The electrochemical reduction of four 4'-halogene-4-aminoazobenzene derivatives was studied in water/ethyl alcohol mixtures at various pH values using cyclic voltammetry (CV), sampled d.c. polarography (SCP), differentialpulse polarography (DPP), chronoamperometry (CA) and constant potential coulometry (BE). The diffusion coefficients and the number of electrons transferred were determined using chronoamperometric Cottrell slope and ultramicroelectrode (UME) steady-state current. The transfer coefficient, heterogeneous rate constant and free energy of reduction of azobenzene derivatives were determined by Koutecky approach. Transfers of four-electron in acidic and two-electrons in basic media were established. Under the conditions employed, the reduction reaction was diffusion-controlled. Also the substituent effect of halogens was examined.
Journal Article•
TL;DR: In this article, the electrochemical behavior of benzo[c]cinnoline and some of its bromo derivatives was studied and two discrete 2-electron reduction waves in acidic and only one wave in basic media in ethyl alcohol-BR buffer system (l:5 v/v).
Abstract: The electrochemical behavior of benzo[c]cinnoline and some of its bromo derivatives was studied. Two discrete 2-electron reduction waves in acidic and only one wave in basic media in ethyl alcohol-BR buffer system (l:5 v/v) were observed. A mechanism for the electrode reaction is proposed. Diffusion coefficients, formal potentials for and the derivatives, the number of electrons transferred were determined by using sampled current polarography, cyclic voltammetry, chronoamperometry, chronocoulometry and constant potential coulometry. Adsorption of the molecules on the surface of the mercury drop was analyzed and this phenomena was exploited to calculate the formal potentials and the diffusion coefficients of benzo[c]cinnolines.
01 Jan 2002
TL;DR: The present work reports on the conditions found suitable to perform such an analysis in the same matrix by slow sweep differential pulse polarography on a controlled-growth mercury electrode (CGME) in the concentration range of 10 -4 to 10 -5 M for both species.
Abstract: Spent nickel-cadmium batteries have become an environmental inconvenience, and many efforts have been undertaken to treat or dispose of them in a safe way. 1,2 Research has been performed for the selective electrodeposition of nickel and cadmium from simulated waste solutions. 3 Work is being carried out in our laboratory with a similar objective. There is an obvious need to analyze both metal concentrations simultaneously and continuously with a fast and precise analytical method in the concentration range of interest. Whereas cadmium is not normally an analytical problem, many different analytical techniques have been proposed for the analysis of Ni, such as spectrophotometry, 4-9 9 atomic absorption, 10,11 flame emission, 12,13 and ion exchange. 14 However, most of these require pieces of somewhat expensive equipment and time-consuming sample preparation procedures. The electrochemical analysis of small amounts of nickel requires relatively inexpensive equipment but presents certain difficulties due to its irreversible reduction behavior. 15,16 In spite of this, it has been successfully accomplished using a variety of techniques such as stripping and voltammetric analysis, 17-22 polarography, 16,23-27 and potentiometry, 28 To the best of our knowledge, the simultaneous analysis of Ni and Cd by differential pulse polarography has not been reported yet. The present work reports on the conditions found suitable to perform such an analysis in the same matrix by slow sweep differential pulse polarography on a controlled-growth mercury electrode (CGME) in the concentration range of 10 -4 to 10 -5 M for both species. In addition to the simplicity of the analytical procedure, the transfer of the analyte to the polarographic cell is straightforward and does not require a special preparation protocol. The precision obtained in the Ni analysis is similar to, or even higher than, that of most of the procedures mentioned earlier, and that of Cd is also found to be very high.
Patent•
06 Mar 2002
TL;DR: An oscilloscopic polarography for measuring S in petroleum fraction and product features that its supporting electrolyte is the mixture of sulfuric acid, methanol and toluene, and its start potential for scanning is 0.116 V as mentioned in this paper.
Abstract: An oscilloscopic polarography for measuring S in petroleum fraction and product features that its supporting electrolyte is the mixture of sulfuric acid, methanol and toluene, and its start potentialfor scanning is 0.116 V. Its advantages include wide linear range and broad spectrum.
Journal Article•
TL;DR: In this article, the reduction of 3-(4'-methyl) phenylazo-8-aldehydo-4-methyl coumarin takes place in a single two electron transfer, a diffusion controlled irreversible wave in a B.R. buffer at d.m.
Abstract: The reduction of 3-(4'-methyl) phenylazo-8-aldehydo-4-methyl coumarin takes place in a single two electron transfer, a diffusion controlled, irreversible wave in a B.R. buffer at d.m.e. and glassy carbon electrodes owing to the reduction of azo group. Based on cyclic voltammetry, polarography, coulometry, product identification, a reaction mechanism is suggested to account for the reduction mechanism. Kinetic parameters, i.e. Charge transfer coefficient (α n ) and forward rate constant (K 0 f , h ) have also been calculated.
TL;DR: In this paper, the electrochemical reduction behavior of two dinitroaniline herbicides, Butralin (BN) and Isopropalin (IN), at a mercury electrode is described based on different voltammetric techniques in various buffer solutions at different pH values.
Abstract: The electrochemical reduction behavior of two dinitroaniline herbicides, Butralin (BN) and Isopropalin (IN), at a mercury electrode is described based on different voltammetric techniques in various buffer solutions at different pH values. The nature of the electrode process has been examined. A reduction mechanism was proposed. Britton–Robinson (BR) buffer of pH 4.0 was found to be best media for the analysis of the compounds. Both standard addition and calibration methods were used for analysis. The detection limits were found to be 6 × 10−8 M (M = mol dm−3) for BN and for 1.5 × 10−8 M for IN. A differential pulse polarographic method was developed for the determination of the herbicides in grains and soils as well as water samples.