Showing papers on "Polarography published in 2016"

Graphene oxide-assisted synthesis of bismuth nanosheets for catalytic stripping voltammetric determination of iron in coastal waters

Abstract: The article describes the synthesis of bismuth nanosheets (BiNSs) in the presence of a small quantity of graphene oxide (GO) which is helpful for the formation of two-dimensional BiNSs and improves dispersity. The material, when placed on a glassy carbon electrode (GCE), is shown to enable catalytic stripping voltammetric determination of total dissolved iron without the need for adding a complexing agent. The average thickness and length of the BiNSs are 3 to 4 nm and 100 to 200 nm, respectively. The unique nanostructure of the BiNSs, the ability of Bi to form alloys with metal, and the current amplification of the catalytic system make the modified GCE an excellent choice for electrochemical determination of Fe(III). Under the optimal conditions, the electrode has a linear response to Fe(III) in the 0.01 to 20 μM concentrations range, with a lower detection limit of 2.3 nM. The electrode was successfully applied to the sensitive determination of Fe(III) in coastal waters.

A nanocarbon paste electrode modified with nitrogen-doped graphene for square wave anodic stripping voltammetric determination of trace lead and cadmium

Abstract: A nano-carbon paste electrode was modified with nitrogen doped graphene and applied to square wave anodic stripping voltammetric determination of lead(II) and cadmium(II). The modified electrode was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Key parameters affecting the performance of the sensor such as pH value, content of modifier, deposition potential and time were optimized. Under optimized conditions, the electrode exhibits linear response to lead (at about −0.56 V) and cadmium (at about −0.77 V) in the range between 10 pM to 1 nM, and the detection limits are 8.0 pM for cadmium(II) and 5.0 pM for lead(II), respectively. The sensitivity, selectivity and simplicity of the method are comparable to, or even better than those reported earlier.

Determination of Methyl Violet 2B using Polarographic and Voltammetric Methods at Mercury Electrodes

Abstract: Direct current tast polarography and differential pulse polarography at a dropping mercury electrode and direct current voltammetry, differential pulse voltammetry, and differential pulse adsorptive stripping voltammetry at a hanging mercury drop electrode were employed for the electrochemical characterization and determination of methyl violet 2B in buffered aqueous media and model water samples The optimum medium for all techniques was 004 mole per liter Britton-Robinson buffer at pH 40 The limits of quantification for methyl violet 2B were 17 micromole per liter (direct current tast polarography at the dropping mercury electrode), 016 micromole per liter (differential pulse polarography at the dropping mercury electrode), 65 nanomoles per liter (direct current voltammetry at the hanging mercury drop electrode), and 45 nanomoles per liter (differential pulse voltammetry at the hanging mercury drop electrode) The lowest limit of quantification of 13 nanomoles per liter was obtained using d

A highly sensitive electrochemical determination of Isoniazid in pharmaceutical preparation by differential pulse Polarography

Abstract: A simple strategy and highly sensitive electrochemical method was developed and described in Britton _ Robinson buffer for isoniazid determination by Differential Pulse Polarography (DPP). A dropping mercury electrode (DME) was used to characterize the performance of the sensor. The reduction process on the (DME) gave a rise with one peak over Ep-1.17 v (vs. Ag/AgCl/), within the studied pH range (2 – 9), 3M KNO3 as a supporting electrolyte and 4mm mercury drop size at 25°C. A standard calibration plot was conducted in the range between 0.050.40μg.ml. The monitored differential pulse current was directly proportional to the concentration of Isoniazid and it showed a linear response in the studied range (correlation coefficient (r) = 0.9997) and the detection limit was 0.05μg. ml . This method effectively applied in commercial Isoniazid pharmaceuticals.

Catalytic And Kinetic Waves In Polarography

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Polarographic and voltammetric determination of genotoxic 4-nitroindane at mercury electrodes

Abstract: Determination and electrochemical investigation of genotoxic nitrated polycyclic aromatic hydrocarbon 4-nitroindane (4-NI) were carried out using direct current tast polarography (DCTP) and differential pulse polarography (DPP) at a classical dropping mercury electrode (DME) and using direct current voltammetry (DCV), differential pulse voltammetry (DPV), and cyclic voltammetry (CV) at a hanging mercury drop minielectrode (HMDmE). The following optimal media for the determination of 4-NI were found: methanol—Britton-Robinson (BR) buffer of pH 12.0 (1:1) for DCTP and DPP, methanol—BR buffer of pH 9.0 (1:9) for DCV, and methanol—BR buffer of pH 8.0 (1:9) for DPV. For CV investigation, mixtures of methanol—BR buffer of pH 3.0, 8.0, and 12.0 (1:1) were used. The limits of quantification were: 0.65 µmol dm−3 (DCTP at the DME), 0.10 µmol dm−3 (DPP at the DME), 0.075 µmol dm−3 (DCV at the HMDmE), and 0.070 µmol dm−3 (DPV at the HMDmE). An attempt to increase the determination sensitivity using adsorptive accumulation of 4-NI on the HMDmE surface was not successful. The newly developed polarographic and voltammetric methods were successfully applied for the determination of 4-NI in model samples of drinking and river water.

Glycine adsorption on a mercury electrode modified by neodymium

Abstract: Ranges of neodymium reduction potentials in aqueous solutions of potassium chloride at pH = 2 and in solutions containing glycine were determined by differential pulse polarography. The glycine complex with neodymium is not formed in the range of the amino acid concentration 0.001–0.12 M. Glycine adsorption on a mercury electrode and on an electrode modified with neodymium was studied by the cyclic voltammetry method.

Techniques Of Oscillographic Polarography

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Redox behavior, chromatographic and spectroscopic characterization of some reactive π-conjugated 4′-tricyanovinylhydrazone dyes

Abstract: A series of π-conjugated nonlinear 4′-tricyanovinylhydrazone (TCH) dyes was synthesized and characterized. The redox behaviors of the TCH dyes were studied by direct current (DC), and derivative polarography (DP), cyclic voltammetry (CV) and controlled potential coulometry (CPC). Excluding the nitro derivatives, the DC and DP polarograms of the compounds at pH < 5 showed two irreversible waves (peaks) corresponding to reduction of the CC– and the hydrazone (CN–) groups. The DC and DP polarography of the nitro derivatives at pH < 5 showed three waves (peaks). Plots of cathodic peak current (ip,c) vs. square root of scan rate (ν1/2) and log ip,c vs. log ν at −0.59 and −0.93 V at pH 4.46 were linear. The kinetic parameters (log kof,h, ΔG* and D) of the compounds were determined. Poor correlations for substituents on the E1/2 of the dyes with the Hammett substituent constants were noticed. Based on the chromatographic separation, spectroscopic characterization and molecular weight determination of the end products of the electrolyzed species of 4′-nitrotricyanovinylhydrazone, an electrochemical reduction mechanism is proposed.

Polarographic Study of Meta-Hydroxyacetanilide and its Determination

Abstract: Present paper deals with polarographic study of effect of maxima suppressors and supporting electrolytes on anodic waves of meta-hydroxyacetanilide and polarographic determination of meta-hydroxyacetanilide under optimum concentration of maxima suppressors and supporting electrolytes. The polarographic method has been developed to study qualitatively the effect of maxima suppressor (fuchsin) and supporting electrolyte (nitric acid) on oxidation wave of meta-hydroxyacetanilide. Polarograms of system were recorded between 500 to 1300 mV by using Rotating Platinum micro Electrode as anode and Saturated Calomel Electrode as cathode on D.C. Recording Polarograph using Omniscribe recorder. It shows a similar behavior to that observed for paracetamol. It produces anodic wave at rotating platinum electrode. The oxidation yields the 3-N-acetylaminosemiquinone and represents a reversible reaction. Polarographically a value of 900 mV is found for decomposition potential of meta-hydroxyacetanilide. Wave analysis point to 1-electron step for each wave. Waves of meta-hydroxyacetanilide are only proportional to concentration at low concentrations.

Development and validation of differential pulse polarographic analysis of fenofibrate in pure and pharmaceutical dosage forms using dropping mercury electrode

Abstract: Objective: An easy, fast, accurate and sensitive differential pulse polarographic analysis for determination of fenofibrate (FEN) in pure and pharmaceutical dosage forms using dropping mercury electrode (DME) was applied. Methods: The method involves the electrochemical reduction of fenofibrate at DME by differential pulse polarographic analysis (DPPA). Different buffer solutions were used over a wide pH range (1.0–10.0). The best definition of the analytical signals was found in lithium perchlorate trihydrate buffer at pH 6.0 containing 24% (v/v) acetonitrile at-994 to-1025mV (versus Ag/AgCl). Results: Under optimized conditions the peak current (I p ) is linear over the range 0.0361-3.608 μg/ml. The DPPA was used successfully for the determination of FEN in pure and pharmaceutical dosage forms. The relative standard deviation did not exceed 2.1% for the concentration of FEN 0.0361 μg/ml. Regression analysis showed a good correlation coefficient (R 2 = 0.9994) between Ip and concentration at the mentioned range. The limit of detection (LOD) and the limit of quantification (LOQ) was to be 0.0025 and 0.0076 μg/ml, respectively. The proposed method was validated for linearity, precision and accuracy, repeatability, sensitivity (LOD and LOQ), robustness and specificity with an average recovery of 99.8-100.6%. Conclusion: The developed method is applicable for the determination of FEN in pure and different dosage forms with the assay of marketed formulations 99.8-104.0% and the results are in good agreement with those obtained by square-wave voltammetry (SWV) reference method. Keywords: Differential pulse polarographic analysis, Fenofibrate, Pharmaceutical formulations

Single Pulse Voltammetry: Reversible Electrochemical Reactions

Abstract: In a single potential step voltammetric technique, several constant potentials (of increasing amplitude) are applied with a time length t 1 When stationary electrodes are used, the time interval between two consecutive potentials must be much greater than t 1, for the initial conditions to be restored (Scheme 21) If a Static Mercury Drop Electrode (SMDE) is used, the initial conditions are simply restored by making the drop fall The measured current at a fixed time value \( t={t}_1 \) is plotted versus the corresponding potential steps discretely [1–3] The resulting current–potential curve has a sigmoidal shape whose position and slope depend on the reversibility of the electrode process and the wave height is independent of the electron transfer rate At each fixed potential value, the current–time variation (which has a typical cottrellian behavior for reversible processes at planar electrodes when considering diffusive transport only) can be registered If the length time is in the range 2–200 ms, the electrochemical technique is called Normal Pulse Voltammetry (NPV), originally known as Normal Pulse Polarography (NPP) This technique was introduced by Barker [5–7] and it was originally designed for the Dropping Mercury Electrode (DME), in which the potential pulse is applied at the end of the life of the drop, with the current being dependent on the relation between the pulse time and the drop lifetime The main reason for measuring the current at the end of short time intervals is to eliminate the capacitative component (see Sect 19) in order to optimize the sensitivity Today the DME electrode is scarcely used and most electrochemical techniques are used at stationary electrodes

Simulation of differential pulse polarography of irreversible EC mechanism

Abstract: A reversible electrode reaction that is followed by totally irreversible chemical reaction is investigated theoretically. The influence of chemical reaction on two components of the net response of differential pulse polarogram is analyzed. It is demonstrated that this EC mechanism depends on two kinetic parameters and that their critical values can be used for the measurement of the rate constant of chemical reaction.

Polarography of Te (IV) Anions in Neutral Solutions in Presence of 2,2'- Dipyridyl and Fe(dipy)3 2+ - Complexes

Abstract: The electroreduction of Te (IV) ions in neutral non-buffer solutions containing 2,2'-dipyridyl (4⋅10 -5 - 4⋅10 -3 M) or tris-dipyridyl iron (II) complexes is studied by the polarographic method. NaF (0.01-0.5 M) or NaNO 3 (0.1-1 M) are used as supporting electrolytes. The mechanism of electrochemical reactions of Te (IV) anions on mercury electrodes in the presence of the additives is discussed. The electroreduction of Te (IV) anions is shown to proceed through electron transfer and proton addition. The obtained results point to a considerable influence of electric double layer structure on electrochemical reactions of Te (IV) ions in the presence of inorganic and specifically adsorbed organic compounds in the electrolyte. It is shown, that 2,2'-dipyridyl does not form complexes with Te (IV) anions. Having been adsorbed on the surface of mercury electrode, 2,2'-dipyridyl complexes increase negative Ψ '-potential that results in a shift of Te (IV) electroreduction wave to more negative potentials and decrease in the current of Te (IV) wave and peak at -1.19 V. It is shown that 2,2'-dipyridyl molecules at ε > 0, ( ε – charge of an electrode) are adsorbed in plane orientation, and at ε < 0, plane or vertical. Vertically adsorbed molecules cause a significant decrease in the double layer capacitance. At negative potentials orientation of 2,2'-dipyridyl molecules changes from plane to vertical with the increasing 2,2'-dipyridyl concentration. This change of orientation results in a typical maximum capacitance emerging in the potential range of -0.7 to -1.2 V. It is shown that the supporting electrolyte, 2,2'-dipyridyl and Fe(dipy) 3 2+  have influence on the electroreduction of Te (IV) anions in neutral non-buffer solutions through a change in the Ψ '-potential of mercury electrode.