Showing papers on "Polarography published in 2008"

Electrochemical Determination of HIV Drug Abacavir Based on Its Reduction

Abstract: Abacavir (I), a drug used in the treatment of HIV, is electrochemically reduced at the dropping mercury electrode in a four-electron process, similar to structurally related adenine (III) and adenosine triphosphate (IV). To undergo the reduction, the species is protonated in the vicinity of the electrode. The protonations take place on the 6-amino group and on one of the pyrimidine ring nitrogens. The role of covalent hydration of the pyrymidine ring has been interpreted. Best suited as supporting electrolytes for analytical purposes are solutions of 0.1−1.0 M sulfuric, perchloric, or hydrochloric acids. Procedures of analyses of tablets containing I were established and validated, based on peak currents obtained by linear sweep, differential pulse, or square-wave voltammetry with a hanging mercury drop electrode as indicator electrode. The procedure proved to be more sensitive and more reliable than that based on oxidation on a glassy carbon electrode, proposed previously.

Determination of losartan and triamterene in pharmaceutical compounds and urine using cathodic adsorptive stripping voltammetry.

Abstract: A square-wave voltammetric procedure for the electroanalytical determination of losartan and triamterene in Britton-Robinson buffer (pH 3.0, 0.1 mol L-1) as a supporting electrolyte containing 30 ng mL-1 of copper ions was developed. Opposite to the case of triamterene, losartan can not be reduced at a mercury electrode alone, but a new peak appears at -0.25 V in the presence of copper due to the formation of a complex between copper(II) and losartan. An accumulation potential of -0.30 V during 80 s for the prior adsorption of losartan-copper(II) and triamterene on the electrode surface was used. The response of the system was found to be linear in the range of 30.0 - 270.0 nmol L-1 for losartan and two linear dynamic ranges containing 0.5 - 200.0 and 200.0 - 400.0 nmol L-1 of triamterene. The limits of detections were 9.7 and 0.3 nmol L-1 for losartan and triamterene, respectively. The relative standard deviations for five replicate analyses of 100.0 and 10.0 nmol L-1 losartan and triamterene were 5.5%. Applicability to assay the drugs in urine and pharmaceutical formulations was illustrated with satisfactory results. The direct-current polarography of triamterene indicates that the reduction of a related drug is strongly dependent on the pH of the solution. A linear segment was found with slope value of -63.6 mV pH-1 in the pH range of 2.0 - 6.0. The stoichiometry and complex formation constant (β) for losartan-Cu(II), number of transfer electrons (n), transfer coefficients (α) and number of proton transfers were also estimated.

Determination of etofibrate, fenofibrate, and atorvastatin in pharmaceutical preparations and plasma using differential pulse polarographic and square wave voltammetric techniques.

Abstract: Etofibrate, fenofibrate, and atorvastatin were determined in their pharmaceutical preparations and human plasma using differential pulse polarographic and square wave voltammetric techniques by reduction at a dropping-mercury working electrode versus Ag/AgCl reference electrode. The reversibility of the electrode reactions was tested using cyclic voltammetry, and they were found to be irreversible reduction reactions. Optimum conditions such as pH, scan rate, and pulse amplitude were studied, and validation of the proposed methods was performed. The proposed methods proved to be accurate, precise, robust, and specific for determination of the 3 drugs. The relative standard deviation values were <2%, indicating that these methods are precise. Limits of detection and quantitation were in the ranges of 0.037-0.21 and 0.12-0.71 microg/mL, respectively, indicating high sensitivity.

Simultaneous Determination of Trans-Cinnamaldehyde and Benzaldehyde in Different Real Samples by Differential Pulse Polarography and Study of Heat Stability of Trans-Cinnamaldehyde

Abstract: A simple, sensitive, and accurate differential pulse polarography method for simultaneous determination of trans-cinnamaldehyde and benzaldehyde in food and drug samples were developed. DC polarography, CV, and coulometric techniques were used for investigation the electrochemical behavior of both compounds. In phosphate buffer (pH = 8.2) and 10% v/v of methanol the differential pulse voltammograms of trans-cinnamaldehyde (−1.05 V) and benzaldehyde (−1.31 V) display reproducible peaks. Under these conditions a strict linearity between both analyte concentrations and their peaks height were observed. The detection limits were calculated to be 2.5 × 10−8 and 1.2 × 10−8 M for trans-cinnamaldehyde and benzaldehyde in pH = 8.2, respectively. The relative standard deviations for 1.0 × 10−6 M of both analytes were 2.04 and 1.18. The heat stability of trans-cinnamaldehyde was studied, and it was found that trans-cinnamaldehyde undergoes a heat-induced decomposition at low temperature (>70°C) to produce b...

Electrochemical determination of muscle relaxant drug tetrazepam in bulk form, pharmaceutical formulation, and human serum

Abstract: Tetrazepam dissolved in the Britton-Robinson universal buffer of various pH values (2.5–11.5) containing 10 vol. % of ethanol was reduced at the mercury electrode in a single 2-electron irreversible step due to reduction of the 4,5 C=N double bond of the seven-membered ring. Differential pulse polarography (DPP) and adsorptive cathodic stripping voltammetry (AdCSV) techniques (Linear sweep LS, differential pulse DP and square-wave SW modes) for quantification of tetrazepam in bulk form and in myolastan tablets are presented. Moreover, the described linear sweep, differential pulse, and square-wave adsorptive cathodic stripping voltammetry was successfully applied in quantification of tetrazepam in spiked human serum without any prior extraction of the drug. The obtained results showed an increased sensitivity of the described electro-analytical procedures for the quantification of tetrazepam in the following order DPP, DP-AdCSV, LS-AdCSV, and SW-AdCSV, since the observed limits of tetrazepam quantitation by these electroanalytical techniques were 5 × 10−6 mol L−1, 3 × 10−7 mol L−1, 1 × 10−8 mol L−1, and 3 × 10−9 mol L−1, respectively.

Chemometric determination of rabeprazole sodium in presence of its acid induced degradation products using spectrophotometry, polarography and anodic voltammetry at a glassy carbon electrode.

Abstract: Chemometric stability indicating methods are presented for the determination of rabeprazole sodium in presence of its acid induced degradation products using spectrophotometry, differential pulse polarography and differential pulse anodic voltammetry at a glassy carbon electrode. The applied chemometric techniques are multivariate ones including classical least squares (CLS), principal component regression (PCR) and partial least squares (PLS). A difference spectrophotometric (DeltaA) method has also been applied. To develop the multivariate calibrations, a training set was used, consisting of 20 mixture solutions of rabeprazole sodium and its degradation products. These mixtures show percentage degradation ranging from 0.5-65%, 0.5-95% and 0.6-75% for the spectrophotometric, polarographic and anodic voltammetric calibrations, respectively. The UV absorbances were recorded in 0.1 M NaOH within the wavelength range 220-340 nm at 2 nm intervals. The polarograms and anodic voltammograms were recorded in Britton-Robinson buffer (pH 8.0) within the potential range -500 to -1508 and 400 to 1192 mV at 6 mV intervals with a pulse amplitude of -100 and 50 mV, sweep rate of 15 and 10 mV s(-1) and pulse interval of 0.4 and 0.6 s for the polarographic and anodic voltammetric methods, respectively. All the studied methods have been validated and successfully applied to the determination of rabeprazole sodium in tablet dosage form. The results were statistically compared to those obtained using a published HPLC method. No significant difference has been found.

Study of Complex Formation Between 5,7-Diiodo-8-hydroxyquinoline and Zn2+, Cd2+, Pb2+ and Tl* Cations in Binary Non-Aqueous Solvents Using Square Wave Polarography Technique (SWP)

Abstract: The complexation reaction between Zn 2+ , Pb 2+ , Cd 2+ and T 1+ cations by 5,7-diiodo-8-hydroxyquinoline (IQN) was studied in the Dimethylformamide /Acetonitril (DMF-AN) binary system using square wave polarography technique. The stoichiometry and stability of the complexes were determined by monitoring the shifts in half-wave or peak potential of the polarographic waves of metal ions against the ligand concentration. The stoichiometry of the complexes was found to be 1:1. The results obtained show that there is an inverse relationship between the formation constant of the complexes and the donor number of solvent base on the Guttmann donocity scale. In all cases the formation constants increased with increasing amounts of AN in these binary systems. The selectivity order for IQN complexes with the cations is Zn 2+ > Pb 2+ > Cd 2+ > T1 + .

Adsorption voltammetry of the zirconium-alizarin red S complex at a multi-walled carbon nanotubes modified carbon paste electrode

Abstract: We used a carbon paste electrode modified with multi-walled carbon nanotubes as a working electrode and studied the electrochemical behavior of zirconium-alizarin red S complex on it. It was found that the modified electrode exhibited a significant catalytic effect toward the reduction of free alizarin red S and the complex. The second derivative linear scan voltammograms of the complex were recorded by a polarographic analyser from 0 to −1000 mV (vs. SCE), and it was found that the complex can be adsorbed on the surface of the modified electrode, yielding a peak at about −470 mV, corresponding to the reduction of alizarin red S in the complex. The linear range was found to be 2.0 × 10−11–8.0 × 10−7 mol L−1, and the detection limit was 1.0 × 10−11 mol L−1 (S/N = 3) for 3 min accumulation. The procedure was successfully applied to the determination of trace amounts of zirconium in the ore samples.

Alternating current anodic stripping voltammetry in the study of cadmium complexation by a reference Suwannee river fulvic acid: a model case with strong electrode adsorption and weak binding

Abstract: The possibilities of anodic stripping voltammetry (ASV) using an alternating current (AC) scan in the stripping step have been checked through the study of the complexation of cadmium by Suwannee river fulvic acid (SRFA), a reference fulvic acid from the International Humic Substances Society. Because of the strong electrode adsorption of SRFA, AC mode appears to be a good approach to the study when proper selection of the phase angle is made. The goodness of AC mode in ASV has been demonstrated, and the complexation constant of 3.71 ± 0.04 determined is in good agreement with the value of the constant obtained by the reference technique of reverse pulse polarography. Some particularities of SRFA have been observed, among them its homofunctional and strongly heterogeneous behaviour in cadmium complexation and the impossibility of avoiding electrode adsorption problems in ASV measurements at very low metal concentrations.

Analytical Voltammetry and Polarography

Abstract: The article contains sections titled: 1. Introduction 2. Techniques 2.1. Direct Current Polarography 2.2. Pulse Techniques 2.3. Alternating Current Polarography 2.4. Linear-Sweep and Cyclic Voltammetry 2.5. Chronopotentiometry 2.6. Stripping Techniques 3. Instrumentation 4. Evaluation and Calculation 5. Sample Preparation 6. Supporting Electrolyte Solution 7. Application to Inorganic and Organic TraceAnalysis

Comparison of differential pulse and alternating current polarography in the soft-modelling study of the complexation of Cd(II) by the fragment Cys-Gly and by the phytochelatin (γ-Glu-Cys)2Gly

Abstract: A comparison of a differential pulse polarographic with a phase sensitive alternating current polarographic study of the Cd-Cys-Gly and Cd-PC2 systems [PC2 being a phytochelatin of general structure (γ-Glu-Cys) n -Gly, with n = 2] has been performed. The chemometric multivariate curve resolution method with alternating least squares was applied in the experimental data analysis. The results obtained by both polarographic techniques have made it possible to find out the formation sequences of the complexes and their final stoichiometries. The alternating current polarograms compared with the differential pulse ones show some differences (a new signal and an important shift of peak potentials), which anyway are consistent with some of the conclusions obtained by differential pulse polarography. This fact implies that although the alternating current polarography results need some corrections before data treatment, they provide extra information that complements the conclusions achieved by differential pulse polarography.

A Contribution to the Elucidation of the Reduction Mechanism of 2-Chloroisonicotinic Acid on Mercury Electrodes

Abstract: This paper presents polarographic (dc and differential pulse) and voltammetric (linear-sweep cyclic voltammetric) studies of the electroreduction of 2-chloroisonicotinic acid (2-chloro-4-pyridinecarboxylic acid), 2-CISO, at mercury electrodes The dissociation constants of 2-CISO were obtained from the UV-visible absorption spectra (pK of 05 ± 003 corresponding to the -COOH group) and by potentiometric titration (pK of 346 corresponding to the protonation-dissociation of the heterocyclic nitrogen) The electrochemical studies were performed in the acidity range 27 M H 2 SO 4 to pH 7 Above the last pH value no signals were observed The overall reduction process involves the uptake of four electrons Kinetics parameters such as Tafel slopes and electrochemical reaction orders have been determined at potentials corresponding to the foot of the waves From the results a reaction mechanism can be proposed, consisting of an electrochemical-chemical process having two reversible electron transfers preceding a chemical step At the scan rates used in cyclic voltammetry, the rate-determining step is the second irreversible electron transfer At pH > 05 the recombination of the carboxylate anion with the H + ion takes place prior to the reduction process

Electrochemical desulfurization of (1-adamantyl)(alkylsulfonyl)pyridines

Abstract: The electroreduction of 4-(1-adamantyl)-2-(alkylsulfonyl)pyridines and 2-(1-adamantyl)-4-(tert-butylsulfonyl)pyridine was studied by polarography and preparative electrolysis on the mercury cathode at various compositions of the supporting electrolyte. Under the preparative electrolysis conditions, the CPy-S bond is predominantly cleaved to form the corresponding adamantylpyridines. The conditions for selective electrochemical desulfurization were found.

Spectral and polarographic determination of eprosartan. Kinetic studies of the oxidation of eprosartan using a platinum electrode.

Abstract: Two simple and sensitive methods are presented for the determination of eprosartan in pharmaceutical preparations. The first method, spectrophotometry, was based on the oxidation of this drug by ammonium cerium (IV) nitrate in the presence of perchloric acid with subsequent measurement of the absorbance at 326 nm; this principle was adopted to develop a kinetic method for the determination of eprosartan in dosage forms. The second method, differential pulse polarography, was based on measuring the peak height at -1300 mV, corresponding to the reduction of the drug in Britton-Robinson buffer (pH 3). The proposed methods proved to be accurate and precise and can be applied for the routine analysis of this drug in commercial dosage forms, without interference from the excipients. The work was extended to study the electrochemical oxidation of eprosartan at different electrolysis currents (10-40 mA). The electrochemical decomposition products were characterized by UV/visible spectroscopy; the decomposition rates follow first order reactions and increase with raising the current. The degradation was found to be faster in basic than acidic medium. The thermodynamics for electrochemical decomposition were also evaluated at different pH values.

Theory of polarographic currents

Abstract: INTRODUCTION Since the invention of the polarographic method in 1922 attention has been paid primarily to theoretical aspects of the method. Heyrovsk and coworkers were interested in the problems of hydrogen evolution at the dropping mercury electrode (DME), in the reduction of oxygen-containing anions, in anodic reactions of anions connected with insoluble salt formation, etc. Shikata, Tachi and coworkers investigated mainly electrode processes of organic compounds with particular reference to the structural aspects. At present the theory of classical d.c. polarography is in many ways a closed subject. Rapid developments are taking place only with regard to processes influenced in some part by adsorption, either of electro-inactive species or reactants and products of electrode reactions. With this in mind I intend to present first a brief review of those fields. Later I shall be concerned in more detail with the adsorption processes in polarography.

Voltammetry of Potassium Octyl Xanthate at Mercury Electrode

Abstract: Electrochemical studies of potassium octyl xanthate at the mercury electrode reveal that the product of the anodic reaction is strongly adsorbed at the mercury surface as indicated by a prewave. Th...

Trace determination of zirconium using anodic adsorptive voltammetry at a carbon paste electrode modified with multi-walled carbon nanotubes

Abstract: A carbon paste electrode modified with multi-walled carbon nanotubes (MWCNT) was prepared and the determination of ultra trace amount of zirconium based on the anodic adsorptive voltammetry of the zirconium-calcium-alizarin red S mix-polynuclear complex is described in this paper for the first time. The results showed that the sensitivity and the selectivity of the method are excellent. The second derivative linear scan voltammograms of the complex were recorded by polarographic analyzer from 200 to 1200 mV (vs. SCE) and it was found that the complex can be adsorbed on the surface of the electrode, yielding a peak at about 840 mV, corresponding to the oxidation of ARS in the complex. The peak current increases linearly with Zr (IV) concentration in the range of 6.0×10−12-6.0×10−11 mol·L−1 (accumulation time 120 s), 6.0×10−11-2.0×10−9 mol·L−1 (accumulation time 90 s) and 2.0×10−9-1.0×10−7 mol·L−1 (accumulation time 60 s) and the detection limit (S/N = 3) is 2.0×10−12 mol·L−1 (accumulation time 180 s). The procedure has been successfully applied to the determination of zirconium in the ore samples.

Xanthates as selective ligands for voltammetric study of Cu(II) in environmental samples

Abstract: Copper(II) in the presence of potassium n-propyl xanthate (Kpxan) and potassium cyclo hexyl xanthate (Kchxan) in ammonium chloride-ammoniumhydroxidemediumin the pH range 9.2 to 10.6 gives catalytic hydrogen waves at mercury electrode and the peak height is proportional to concentration of metal ion. The method developed is simple, rapid and sensitive without interferences of many metal ions and applicable to the analysis of alloys and agriculture materials.An electrode reaction mechanism based on d.c. polarographic and cyclic voltammetric results of the system is also suggested.

Polarographic study and electrode kinetics of [Zn(II)-antibiotics-cephaloglycin] system vis a vis kinetics of electrode reactions

Abstract: Electrode kinetics and complex formation of Zn(II) using doxycycline, chlortetracycline, oxytetracycline, tetracycline, minocycline, amoxicillin, chloramphenicol and cephaloglycin were reported at pH = 7.30 ± 0.01 in = 1.0 molL-1 NaClO4 used as supporting electrolyte at 25.0°C. Kinetic parameters viz. transfer coefficient (α), degree of irreversibility (λ) and rate constant (k) were determined. The study showed that 'Transition state' behaves between reactant (O) and product (R) response to applied potential. The stability constants varied from 2.14 to 10.31 showing that these drugs or their complexes could be used against Zn toxicity.