Pulse Polarograms Research Articles

Polarograpy of Zn (II)-Tolbutamide complex and its Pharmacological Study

The formation of complexes of tolbutamide and Zn(II) was studied in aqueous media at pH 3.4±0.1 by polarography and spectroscopy. The polarogram indicated formation of complexes between tolbutamide and Zn (II). Tolbutamide produces a well-defined direct current polarogram and differential pulse polarogram in 1M KCl (supporting electrolyte) at pH 3.4±0.1. The stoichiometry of the Zn (II)-tolbutamide complex is 1:1. Antidiabetic studies on the drug and its metal complex have been performed in albino mice. Revealing the complex to be more potent in antidiabetic activity compared to the parent drug.

Simulation of differential pulse polarography of irreversible EC mechanism

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.

Center of Gravity (COG) Method as a Tool in Processing of Voltammetric Signals

AbstractThe center of gravity method (COG) was applied (for the first time) in voltammetry (polarography) as a tool for very precise determination of peak potentials, and signal shifts. Basically, the adjustment of the method consists of finding the optimal fraction of the peak that contains information about peak position, either of original signal or of its 1st or 2nd derivatives, along with optimal selection of parameters for SavitzkyGolay smoothing of original curves and elimination of baseline influence. The principle of the method and its validation were demonstrated and checked on simulated differential pulse polarograms (DPP) representing a series of curves for the determination of stability constants of labile metal complexes (DeFord‐Hume method). It was shown that COG outperforms the classical “one‐point” method (OPM) in precision and accuracy, providing excellent results even if a very large step potential (e.g. 10 mV) was used. The problems of reduced accuracy and precision in case of curved (non‐ideal) baseline and asymmetric peaks were successfully overcome by applying COG on curves transformed by 1st and/or 2nd derivatives. The method was additionally examined in details on a simple experimental dataset of cadmium chloride complexes in 4 mol dm−3 ionic strength solution and on a more complex dataset of uranyl selenate complexes in 3 mol dm−3 ionic strength solution. Stability constants obtained by COG agree well with those in the literature with much better precision than the classical one‐point method (checked by standard error of the fit).

Determination of free metal ion concentrations with AGNES in low ionic strength media

The determination of free metal ion concentrations of heavy metals, like Zn2+ or Cd2+, with AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) requires an adequate selection of parameters such as deposition potential (linked to the gain, [M0]/[M2+]) and deposition time. In systems with low ionic strength, the peak potential of the Differential Pulse Polarogram (DPP) measured with low supporting electrolyte is not always suitable for the computation of the gain with existing expressions. The application of AGNES with a constant potential (regardless of the ionic strength) provides a direct measurement of the metal ion activity. When working with low ionic strength solutions, the selection of appropriate instrumentation is important to avoid changes in liquid junction potentials or leakages from the employed electrodes. The deposition times (for a given gain) have not been found to be greatly affected by the probed ionic strengths when working with just metal. A new strategy for the practical implementation of AGNES to measure free metal ion concentrations in samples with low KNO3 or Ca(NO3)2 concentrations consists in the computation of the deposition potential (to reach a certain gain) from the DPP peak potential at a sufficiently high ionic strength using a new expression. A speciation experiment with Zn2+ and glycine at pHs between 4 and 7.5, where [KNO3]=0.001M, shows that this methodology works well and also proves that it is possible to perform AGNES in systems with very low ionic strength.

Resolving of Voltammetric Data for the Ni–Glycine and Cu–Glycine Complexation Systems with Reversible and Irreversible Electrochemical Response Using MCR-ALS

The Ni–glycine and Cu–glycine systems, which form successive complexes, were studied by differential pulse polarography. The Ni–glycine complexes were inert while the Cu–glycine system showed labile behavior. An irreversible electrochemical response was found for the Cu–glycine system. The data were analyzed both by conventional methods (hard modeling) and the multivariate curve resolution method with alternating least-squares optimization (MCR-ALS, soft modeling approach). Resolving titration data for Cu2+ and Ni2+ with glycine as the complexing ligand shows that this method is a powerful tool for the determination of stability constants of metal complexes, especially when the conventional methods involve complicated and time consuming approaches such as for systems with an irreversible reduction process. Although for labile complexes the current is not always linear with respect to the concentrations, the results obtained by the two approaches are similar, so the variation from linearity of the signals is small and can be neglected. Also, the analysis of the labile complex data by a Gaussian peak adjustment (GPA) algorithm showed that this system has a small deviation from bilinearity. Thus, the MCR method provided good estimations of the complexation parameters, and is suitable for use as a complementary tool for studying systems with successive labile or inert complexes with both reversible and irreversible responses. Differential pulse polarograms were measured at room temperature for buffer solutions with pH = 7.5 and 0.1 mol⋅L−1 ionic strength.

Study of Zn(II)-coumarin complex by electrochemical method with increased anticoagulant potency

The formation of complexes of coumarin and Zn(II) was studied in aqueous media at pH 8.2±0.1 by polarography and spectroscopy. The polarogram indicated formation of complexes between coumarin and Zn(II). Coumarin produces a well-defined direct current polarogram and differential pulse polarogram in 1 m ammonium tartrate (supporting electrolyte) at pH 8.2±0.1. The stoichiometry of the Zn(II)-coumarin complex is 1:1. Anticoagulant studies on the drug and its metal complex have been performed in albino mice, revealing the complex to be more potent in anticoagulation activity compared to the parent drug.

English

Curcumin has anti-oxidative and anticarcinogenic activities. This study shows the electrochemical behaviour of curcumin using polarography, i.e., DC polarography and differential pulse polarography (DPP) methods. In ammonium tartrate as supporting electrolyte, the differential pulse polarogram of curcumin shows two conjugated peaks with peak potential ( Ep ) -1125 mV and -1275 mV vs SCE. However, the direct current polarogram shows only one polarographic wave with E1/2 which was -1275 mV. The developed electrochemical methods have been standardised for the determination of curcumin in extracted sample of natural origin and its pharmaceutical formulation. The electrochemical analysis has been supplemented by ultraviolet and infrared spectral analyses of the samples. Defence Science Journal, 2010, 60(3), pp.255-258 , DOI:http://dx.doi.org/10.14429/dsj.60.351

Polarographic reduction of pralidoxime and obidoxime at hanging mercury drop electrode

The polarographic reduction behavior of Pralidoxime (PRL) and Obidoxime (OBD) at a Hanging Mercury Drop Electrode (HMDE) was exploited for their determination in different samples. Based on the obtained differential pulse polarograms, standard addition method was used to determine these drugs in pharmaceutical formulations and biological fluid samples. Linearity in the peak currents was achieved in the concentration ranges of 5.4 x 10 -8

The role of Fe(II) in the increased medicinal potency of curcumin analyzed by electrochemical methods

The formation of complexes of curcumin and Fe(II) was studied in aqueous media at pH 5.7 ± 0.1 by polarography, amperometry and spectrophotometry. The polarogram indicated formation of complexes between curcumin and Fe(II). Curcumin produces a well-defined direct current polarogram and differential pulse polarogram in 0.1 M ammonium tartrate (supporting electrolyte) at pH 5.7 ± 0.1. The stoichiometry of the Fe(II)-curcumin complex is 1 : 1. Anticancer studies on the drug and its metal complex have been performed against sarcoma cells (in-vitro), revealing the complex to be more potent in anticancer activity compared to the parent drug.

Target transform fitting in a voltammetric study of metal complexation

In this work target transform fitting (TTF) is proposed as a hard-model based data analysis method to analyze differential pulse polarograms recorded in a successive metal complexation system. In such cases, equations for both complexation equilibria and shape of the differential pulse polarogram for individual species are available. Utilizing TTF to fit these models in separate stages, stability constants and E 1/2 values of species were estimated. In the first stage, E 1/2 values of all species were acquired using the shape-equation of voltamograms and projection of a test vector into the row space of data matrix. In the second stage, using equations derived from relationships among species’ concentrations in complexation equilibria and a non-linear parameter fitting algorithm, the optimum values of overall formation constants were estimated. Finally, rank annihilation (RA) method was employed for calculation of diffusion coefficients. In spite of the fact that proposed method is a hard-model based approach, obtained results show that analysis can be performed correctly even in presence of unknown species. The reliability of the method was tested analyzing simulated data and also polarograms obtained from Cd(II) and 1, 10-phenanthroline complexation system. This experimental system yields three successive complexes which are relatively inert from electrochemical point of view. The results were in a good agreement with reported results in the literature.

A Simple Differential Pulse Polarographic Method for the Determination of Artemisinin in Artemisia Annua

A reliable and simple differential pulse polarographic method is presented for the determination of the antimalarial artemisinin in Artemisia annua. The polarographic behaviour of artemisinin was examined in various buffer systems over the pH range 2–10. Artemisinin was irreversibly reduced at the dropping mercury electrode. In 0.1 M KH2PO4, pH 5.5, mixed with methanol (7:3; v/v), the differential pulse polarograms exhibited reproducible peaks at 0.0 V vs. Ag/AgCl and a plot of peak height against concentration of artemisinin was found to be linear over the range 6.4 × 10−7 - 3.2 × 10−5 mol/L (R = 0.9998). The detection limit was calculated to be 58 ng/mL. The polarographic method was applied to the determination of the content of artemisinin in the traditional Chinese herbal drug Artemisia annua L. by using the standard addition method. The proposed DPP method is sensitive, precise and time-efficient and is, therefore, suitable for quantitative analysis of artemisinin in plant extracts.

Determination of the antimalaria drug artemether in pharmaceutical preparations by differential pulse polarography

A differential pulse polarographic method has been developed for the determination of artemether in its pharmaceutical formulations. The polarographic behaviour of artemether was examined in various buffer systems over the pH range 3.0–10.0. In phosphate buffer pH 5.5/methanol solution (7:3, v/v) the differential pulse polarograms displayed reproducible peaks at E p – 0.01 V versus Ag/AgCl. Under these conditions strict linearity between artemether concentration and peak height was observed in 3.4 × 10 −7–3.0 × 10 −5 mol/L concentration range ( R = 0.9998). The detection limit was calculated to be 32 ng/mL. The polarographic method was applied to the determination of the content of artemether in tablets and capsules by using the standard addition method. The analysis of tablets containing 20 mg artemether showed a mean value of 19.73 mg with a relative standard deviation (R.S.D.) of ±1.01%. A content of 39.74 mg artemether was found in 40 mg capsules with a relative standard deviation of ±0.53%. The polarographic method is characterised to be cheap, precise and not time-consuming and can therefore be used for routine analysis of artemether in its pharmaceutical preparations.

Polarographically Active Structural Fragments of Lignin. II. Dimeric Model Compounds and Lignins

Lignin model dimers representing all typical interunit linkages in lignin (β‐O‐4, α‐O‐4, α‐O‐γ, β–5, 5–5, β–β, stilbene, enol ether) were characterized by differential pulse polarography (DPP) and cyclic voltammetry (CV) in DMSO. Polarographic activity was registered for α‐(C˭O)‐β‐O‐4 structures and conjugated double bonds in stilbene and enol ether structures. A structure–chemical reactivity correlation diagram is drawn based on the studies of one‐ and two‐unit model structures of lignin. Peaks in differential pulse polarograms of lignin were assigned to certain functional groups and bond types based on the comparison between the data obtained on model compounds and selectively chemically modified [NaBH4, LiAlH4, CH2N2, (CH3O)2SO2] lignin samples.

Accurate determination of oosporein in fungal culture broth by differential pulse polarography.

A simple and accurate differential pulse polarographic method has been developed for the determination of oosporein in the culture broth of the fungus Beauveria brongniartii. This hydroxybenzoquinone derivative is the only major secondary metabolite secreted by this entomopathogenic fungus, which is used as biological pest control agent (BCA) against Melolontha melolontha larvae. It can be found in the host organism as well as in the formulated product. The polarographic behavior of oosporein was examined in various buffer systems over the pH range 3-10. In Britton-Robinson buffer/methanol solution (3:7 v/v, pH 5.5) the differential pulse polarograms exhibited reproducible peaks at E(p) = -0.18 V vs silver/silver chloride/potassium chloride (3 M). Under these conditions, a plot of peak height vs concentration of oosporein was found to be linear over the range 5.9 x 10(-)(7) to 2.5 x 10(-)(5) M (0.18-7.74 microg mL(-)(1); r = 0.9998). The detection limit was calculated to be 54 ng mL(-)(1). To evaluate the concentration of oosporein, the standard addition method was applied. The analysis of oosporein in the culture broth led to a mean value of 524.9 microg mL(-)(1) broth with a relative standard deviation (S(rel)) of +/-2.6%. The proposed polarographic method is accurate, not time-consuming, and it is of low cost because no separation steps are necessary.

A simple differential pulse polarographic method for the determination of thymoquinone in black seed oil.

A reliable and simple differential pulse polarographic method is described for the determination of thymoquinone in black seed oil. The polarographic behaviour of thymoquinone was examined in various buffer systems over the pH range 5.0-10.0. Thymoquinone is reduced in a single, reversible peak at the dropping mercury electrode. The differential pulse polarogram showed a distinct peak in Sörensen buffer:methanol (3:7, v/v; pH 8.5) at a peak potential of -0.095 V (vs. silver/silver chloride electrode), and a plot of peak height against concentration was found to be linear over the range 0.2-15.0 microg/mL (R = 0.9998). The limit of detection was calculated to be 0.054 microg/mL. The polarographic method has been applied to determine thymoquinone in two black seed oil preparations available on the Austrian pharmaceutical market.

Binding Curve from Normalized Limiting Currents of Labile Heterogeneous Metal‐Macromolecular Systems. The Case of Cd/Humic Acid

AbstractA set of titrations of different amounts of humic acid with cadmium are performed at pH 6.0 and fixed ionic strength (0.1 M KNO3). Both reverse pulse polarograms, which minimize the electrodic adsorption effects on the limiting current, and potentiometric measurements with an ion selective electrode are recorded along the titrations. The free metal concentration is determined from the polarographic measurement by means of an iterative numerical method recently developed. The resulting binding curve is found to agree very well with the one obtained through the potentiometric data obtained along the same titration. After application of the Donnan model to correct for polyelectrolytic effects, different complexation isotherms have been used to fit the specific binding. Complexation parameters for the Cd/HA system obtained with a Langmuir‐Freundlich and Gaussian isotherms are briefly discussed.

Chemical Properties of Co(II) Compound Containing Endocrine Disrupter, Bis-Phenol A

The chemical behavior and properties on the redox state of environmental pollutant has been investigated by electrochemical methods. We carried out to measure the variations in the redox reaction of differential pulse polarogram and cyclic voltammogram. The results observed the influences on redox potential and current of various factors with temperature and pH. These were established factors as the effect of the redox reaction. It can be clearly recognized that the electrode reaction are from qusi-reversible to irreversible processes. Also, it was mixing with reaction current controlled. The bits-phenol A in the waste water was made to compound with cobalt ion and it take away from the separation into compound. The <TEX>$Co(BPA)_2$</TEX> compound was not found to be dissociation in waste water. However, this compound is avery unstable(K=1.02) and for a while, it was to be a dissociation. Therefore, we believed that it was likely to a toxic substance.

Analyses of Adsorption Waves and Digital Simulation on Pulse Polarograms of Benzyl Viologen

Analyses of Adsorption Waves and Digital Simulation on Pulse Polarograms of Benzyl Viologen

Theoretical Analysis of Pulse and Differential Pulse Polarography of Reversible Redox Reaction Complicated by Reactant Adsorption

Pulse and differential pulse polarograms of redox reactions complicated by reactant adsorption with and without lateral attractions in the monolayer are analysed theoretically by using a stationary spherical diffusion model. The continuous shift of the post-peak potential to lower values and the decrease in its half-peak width with increasing bulk concentration of reactant indicate attractions between adsorbed ions or molecules.

Determination of metal ion binding parameters for humic substances

In Part 1 of this series, a straightforward calculation method was applied to the extraction of metal ion binding parameters from reverse pulse polarograms for fulvic substances. In this paper we extend this approach to include ASV pseudo-polarograms. Pseudo-polarography allows measurements to be made at low (environmentally relevant) concentrations and overcomes problems associated with processes occurring during the stripping step. Data presented for simple systems (the labile Pb(II)–pyridine-2,6-dicarboxylic acid, and the inert Pb(II)– and Cu(II)–EDTA systems) establish the validity of the pseudo-polarographic approach. Application of this methodology to Pb(II) and Cu(II) complexation by Suwannee River fulvic acid (SRFA) reveals that the complexation of Pb(II) is less heterogeneous than that of Cu(II). As compared to reverse pulse polarography (RPP), the lability of the complexes was reduced under ASV conditions (greater ligand excess). Pb(II)–SRFA behaviour approached non-lability, and although binding parameters could be determined, the values are probably influenced by loss of lability. For Cu(II)–SRFA, considerable loss of lability occurred and binding parameters could not be calculated. For adequate sensitivity, minimisation of adsorption interferences, and elimination of stripping step effects, we recommend the use of pseudo-polarograms constructed from plots of DC-ASV peak area as a function of deposition potential.