Static Mercury Drop Electrode Research Articles

Measuring the levels of Zn, Cu, Pb and Cd via the polarography method in fermentative pickled cucumbers purchased from Tehran market, Iran

Pickled cucumber is frequently consumed by Iranians. According to the production process, there are two forms of pickled cucumber including industrial and fermentative. There is not an appropriate monitoring system available for the production of the latter form; therefore, high levels of heavy metals might be present in this type of pickled cucumber. Accordingly, so the levels of cadmium, zinc, lead and copper were measured in fermentative pickled cucumbers obtained from the Tehran market via the polarographic method. Polarography is a subclass of voltammetry where the working electrode is a dropping mercury electrode (DME) or a static mercury drop electrode (SMDE), which are useful for their wide cathodic ranges and renewable surfaces. Fifty different samples of pickled cucumbers were purchased from the market. Of each sample, dry ashes were produced. Measurement was repeated three times and the acquired data was then analyzed. The mean levels of zinc and copper in the evaluated samples were significantly lower than the standard limits respectively presented by the EOS and Codex (P value<0.001) while the mean level of cadmium and lead was slightly higher than the standard limit established by Codex with no significant differences observed (P values=0.450 and 0.246, respectively).

Structural and electrochemical properties of two novel CdX2 (X = Br, I) picolinamide complexes

Two novel discrete cadmium(II) complexes, namely [CdBr2(pia)2] (1) and [CdI2(pia)2] (2) were prepared by reactions of aqueous solutions of CdX2 (X = Br, I) salts with picolinamide (pia) in the 2:1 ligand to metal stoichiometric ratio. Both compounds were characterized by elemental analysis, IR-spectroscopy, TG/DSC analyses and electrochemical methods. The electrochemical characteristics of both ligand (pia) and prepared complexes were studied by cyclic and (cyclic) square-wave voltammetry, on a static mercury drop electrode (SMDE), in aqueous media over a wide pH range. The molecular and crystal structure of the compounds was determined by the single crystal X-ray diffraction method. X-ray structure analysis of 1 and 2 have shown that the compounds are isostructural with minor differences in the bond angles of the coordination sphere. In both compounds the Cd(II) ion is coordinated by two halide atoms and two mutually orthogonal picolinamide ligands that act as N,O-chelators in a distorted octahedral arrangement. In the crystal structure, the molecules of 1 and 2 are primarily linked via strong head–to–head amide hydrogen bond interactions forming dimers. In 1 the adjacent dimers are connected via NH⋯Br hydrogen bonds and offset face to face π⋯π interactions that involve pyridine rings, while in the structure of 2, the dimers are connected via CH⋯O, CH⋯N and NH⋯I hydrogen bonds into the final 3D structure. The intermolecular interactions in both crystal structures were further studied by Hirshfeld surface analysis. Electrochemical analysis of 2-picolinamide indicates the irreversible nature of its electro-reduction reaction on SMDE at pH 2. To provide better insight into the redox mechanism and electrokinetic properties of 2-picolinamide, the study of the effect of signal frequency on CSWV response was carried out, too. The electrochemical reduction of complex 2 involves two electron transfer reactions at −0.55 V and −0.83 V, indicating two redox active centers in the molecule, while complex 1 appears to be apparently electro-inactive in the studied potential range.

Voltammetric Behavior and Reliable Method for the Determination of Coccidiostat Robenidine in Animal Feed and Poultry Meat

AbstractThe voltammetric behaviour of coccidiostat robenidine was investigated. The outcomes have revealed that reduction of robenidine causes an appearance of one diffusion‐controlled cathodic peak on a static mercury drop electrode (SMDE) and a silver solid amalgam electrode (p‐AgSAE). The influence of pH, a supporting electrolyte, a scan rate and accumulation parameters was evaluated. The mechanism of robenidine reduction involving two electrons and one proton was studied for the first time. The calibration curves with the wide linear concentration ranges (more than two concentration orders) were obtained under optimized experimental conditions and operating parameters. The reduction current linearly increases when increasing the concentration of coccidiostat. The methods of voltammetric determination of robenidine in feed and meat have been developed. The limits of quantitation of the methods of robenidine determination in feed are 9.5 mg/kg and 2.5 mg/kg on SMDE and p‐AgSAE, respectively. Calculated recoveries ranges of robenidine were between 88.8 % and 101.5 %.

The acid\u2013base and redox properties of menaquinone MK-4, MK-7, and MK-9 (vitamin K2) in DMPC monolayers on mercury

The acid–base and redox properties of the menaquinones MK-4, MK-7, and MK-9 (vitamin K2) have been studied in DMPC monolayers on mercury electrodes. The monolayers were prepared by adhesion-spreading of menaquinone-spiked DMPC liposomes on a stationary mercury drop electrode. All three menaquinones possess {text{p}}K_{{text{a}}} constants outside the experimentally accessible range, i.e., they are higher than about 12. The standard potentials of MK-4, MK-7, and MK-9 in the DMPC monolayers are very similar, i.e., 0.351, 0.326, and 0.330 V (corresponding to the biochemical standard potentials − 0.063, − 0.088, and − 0.085 V).Graphic abstract

Determination of Methimazole in Pharmaceutical Preparation and Human Serum by Square Wave and Differential Pulse Polarographic Methods

Objectives: In this study, the polarographic behaviour of methimazole was studied using cyclic, square wave and differential pulse polarographic methods. Methods: The influence of several variables (including nature of the buffer, concentration, scan rate, drop size, etc.) was examined in square wave and differential pulse polarographic methods for methimazole. The best square wave and differential pulse polarographic responses were obtained in 0.1 M sulfuric acid. The peak currents were measured with a static mercury drop electrode at 0.10 V versus Ag/AgCl. Results: The linearity was established over the concentration range of 5-80 mg/mLfor both methods in supporting electrolyte and human serum. The methods were validated and applied to the determination of methimazole in a commercial tablet. There was no significant differences between the results obtained by square wave and differential pulse polarographic methods. Square wave and differential pulse polarographic methods are also available and applicable for the determination of mentioned substance in human serum. No electroactive interferences from the endogenous substances were found in the serum samples. Mean recovery was 99.9%. Conclusion: They were concluded that the developed methods were accurate, sensitive, precise, reproducible and useful for the quality control of methimazole in pharmaceuticals and spiked serum.

Differential Pulse Polarographic Behavior and Quantification of the Flucloxacillin in Pure and Pharmaceutical Dosage Forms Using a Static Mercury Drop Electrode

Differential pulse polarographic analysis (DPPA) by using static mercury drop electrode (SMDE) for quantification of flucloxacillin (FLUX) in pure and pharmaceutical dosage forms was studied. The optimum conditions for the polarographic signal were determined and a study was made of the different parameters affecting the electrochemical process. The best definition of the analytical signals was found in Britton–Robinson buffer (0.06 M) at pH 4.0 . Under the optimum conditions, liner calibration graph, Ip=f(CFLUX) was obtained in the concentration ranges of 0.1 mM (0.0494 ?g.mL-1) to 26 mM (12.8414 ?g.mL-1) at -940 to -1000 mV (versus Ag/AgCl) with relative standard deviations (RSD) did not exceed 2.4% for the concentrations of FLUX (0.0494 ?g.mL-1). Regression analysis showed a good correlation coefficient (R2=9998) between Ip and concentration over the mentioned range. The limit of detection (LOD) and the limit of quantification (LOQ) were to be 0.0040 and 0.0120 ?g.mL-1, respectively. The proposed method was validated for linearity, precision and accuracy, repeatability, sensitivity (LOD and LOQ), robustness and specificity. The developed method is applicable for the determination of FLUX in pure and different dosage forms in presence a same amount of amoxicillin (AMOX) with average recovery of 99.4 to 102.2 % and the results are in good agreement with those obtained by the HPLC reference method.
  

Polarographic determination of benzotriazoles and their sorption behavior on granular activated carbon

Because of their persistence and unknown environmental risks, the widespread occurrence of benzotriazoles has been gaining increased attention. A highly selective, rapid, and economical method—differential pulse polarography—was developed and applied for the quantitation of commercially significant methylbenzotriazole isomers in environmental samples of relevance to wastewater treatment, non-point source pollution and acid mine drainage. Differential pulse polarography was able to accurately measure aqueous methylbenzotriazole, as well as the methylbenzotriazole fraction that sorbed to activated sludge biomass, subsurface sediments, and activated carbon. Granular activated carbons were characterized for their ability to sequester benzotriazoles from aqueous environments using differential pulse polarography and high-performance liquid chromatography. Langmuir, Freundlich, Toth and Redlich–Peterson isotherm models were compared for their ability to describe benzotriazole partitioning to granular activated carbons under a relatively wide range of water quality conditions. Sorption behavior of 5-methylbenzotriazole was best-described by a Redlich–Peterson isotherm model, where water quality parameters were varied in the following range pH (1 < pH < 5), temperature (5 °C < T < 25 °C), and in the following ranges of an ionic strength (0.005 < M < 0.02). 4- and 5-methylbenzotriazole concentrations determined by differential pulse polarography correlated well with those concentrations measured by high-performance liquid chromatography through an environmentally significant range (0.4–30 mg/L). Using a static mercury drop electrode, the method detection limit was 50 and 40 μg/L for 4- and 5-methylbenzotriazole, respectively. The developed DPP polarographic method was found to be simple, rapid, and it can be applied directly to environmental samples without filtration, extraction, and centrifugation.

Voltammetric Characterisation of Anticancer Drug Irinotecan

AbstractElectrochemical reduction of irinotecan was investigated on a static mercury drop electrode using square‐wave voltammetry. The mechanism of irinotecan electroreduction is a complex, pH‐dependent, quasireversible process and includes the transfer of two electrons and two protons. In acidic medium, the first electron transfer reaction is followed by the chemical reaction, and the product of this chemical reaction undergoes further electrochemical reduction at more negative potentials. Both irinotecan and the product of its reduction adsorb on the mercury electrode surface. Based on the adsorptive character of irinotecan, a new adsorptive stripping square‐wave voltammetric method for its electroanalytical determination has been proposed. The voltammetric response could be used to determine irinotecan in the concentration range from 1×10−7 mol/L to 1.5×10−6 mol/L and from 5×10−9 mol/L to 1.2×10−7 mol/L, if the accumulation time is 20 s and 300 s, respectively. The calculated limit of detection for irinotecan was found to be 8.7×10−9 mol/L (if tacc=300 s).

Development and evaluation of a glassy carbon electrode modified with silver and mercury nanoparticles for quantification of cysteine rich peptides

A glassy carbon electrode,covered with a Nafion film, on which nano-structured bimetallic particles of Ag-Hg were deposited; from now on “the AgHgNpNf/GC electrode”, was used for the indirect determination of cysteine, glutathione and metallothioneins by measuring the catalytic hydrogen evolution signal according to the Brdička reaction using cobalt as a catalyst. Upon successful formation and deposition of the Ag-Hg bimetallic nanoparticles cyclic voltammetry (CV), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the electrode for that specific task. The results showed the electrode to be mechanically resistant even under sonication, stable in its performance, porous, sensitive in its response and of low cost to be built. Differential pulse voltammetry signals for cysteine and glutathione obtained using the AgHgNpNf/GC electrode were qualitatively similar to those reported using a hanging mercury drop electrode, (HMDE), dropping mercury electrode (DME) and static mercury drop electrode (SMDE). Detection limits based on the variability of a blank solution, (3s criterion) calculated for those tests were 0.463μgL−1 and 0.064μgL−1, for cysteine and glutathione, respectively. Based on the Brdička procedure and considering the particular characteristics of the new electrode, some analytical tests were carried out for the indirect determination of the metallothioneins content of samples of blood serum of rats exposed to lead by measuring the evolution of the catalytic hydrogen signal. An average accuracy value around 102%, n=6, and a precision of 0.87%±0.09 were obtained for these tests.

Electrochemical Characteristics of 4‐oxo‐4H‐pyran‐dicarboxylic Acid (Chelidonic Acid) and some of its Metal Complexes

AbstractA few novel metal complexes of chelidonic acid (chelH2), namely [Ca(chel)(H2O)3] (1), [Cu(chel)(H2O)5] ⋅ 2H2O (2) and [VO(chel)(H2O)3] ⋅ 2H2O (3) were prepared, identified by elemental analysis and characterized by electrochemical methods. IR‐spectra and thermal stability in solid state are discussed as well. The electrochemical characteristics of the free chelidonic acid and its complexes 1–3 were studied by (cyclic) square‐wave voltammetry, on static mercury drop electrode (SMDE) and paraffin‐impregnated graphite electrode (PIGE), in aqueous media over a wide pH range. The reduction of chelidonic acid on SMDE is a kinetically controlled electrode reaction, occurring with the transfer of one electron and two protons for 1&lt;pH&lt;6, whereas in very alkaline media the electron transfer is pH independent, i.e. the mechanism of electro‐reduction of chelH2 is proposed. The experimental parameters of the electroanalytical procedure were optimized and the method was applied for the investigation of the metal ion coordination preferences toward chelidonic acid. For the direct determination of solid complexes 1–3, SW voltammetry of microparticles was used.

From mercury to nanosensors: Past, present and the future perspective of electrochemistry in pharmaceutical and biomedical analysis

Polarography was the first developed automated method of voltage-controlled electrolysis with dropping mercury electrode (DME). Then, hanging mercury drop and static mercury drop electrodes were added as an alternative indicator electrode. In this way, polarography turned formally into voltammetry with mercury electrodes in the electroreduction way. Solid electrodes such as noble metal and carbon based electrodes can be used for the investigation of the compounds for both oxidation and reduction directions, which is called voltammetry. The voltammetric and polarographic techniques are more sensitive, reproducible, and easily used electroanalytical methods that can be alternative to more frequently used separation and spectrometric methods. Furthermore, in some cases there is a relationship between voltammetry and pharmaceutical samples, and the knowledge of the mechanism of their electrode reactions can give a useful clue in elucidation of the mechanism of their interaction with living cells. The voltammetric and polarographic analysis of drugs in pharmaceutical preparations are by far the most common use of electrochemistry for analytical pharmaceutical problems. Recent trends and challenges in the electrochemical methods for the detection of DNA hybridization and pathogens are available. Low cost, small sample requirement and possibility of miniaturization justifies their increasing development.

Simultaneous square-wave voltammetric determination of acetazolamide and theophylline in pharmaceutical formulations

Simple, rapid, sensitive and low cost voltammetric method for simultaneous determination of acetazolamide and theophylline in pharmaceutical formulations, was developed using a static mercury drop electrode (SMDE). Well-defined voltammetric peaks were obtained at–0.87 and–1.33 V for acetazolamide and–0.21 V (vs. Ag/AgCl) for theophylline in Britton–Robinson (B–R) buffer (pH 2.4). The reduction peak currents are found to be linearly dependent on the concentration for the both drugs. Calibration graphs were obtained over the concentration range 1.98 × 10–6 to 5.94 × 10–5 M and 2.0 × 10–5 to 5.6 × 10–4 M for acetazolamide and theophylline, respectively. The limits of detection (LOD) and quantitation (LOQ) of the procedure were also presented. Factors such as, pH of supporting electrolyte, equilibrium time, frequency, scan rate and pulse height were optimized. The validated voltammetric method was successfully applied for simultaneous determinations of the two drugs. The procedure does not require any sample pretreatment or timeconsuming separation steps.

Square‐Wave Voltammetry of Electroinactive Surfactants

AbstractUnder the influence of previously published and some new theoretical results, potential‐ dependent adsorption and desorption of model electroinactive surfactants Triton X‐100 (T‐X‐100 or polyethylene glycol p‐(1,1,3,3‐tetramethylbutyl)‐phenyl ether) and sodium dodecyl sulfate (SDS) on the static mercury drop electrode (SMDE) were studied by square‐wave voltammetry (SWV). Although (according to the theory) the resulting current – potential curve should consist of two highly separated peaks, only desorption signal could be seen on each experimentally obtained voltammogram, most probably because of the limitations concerning the available potential range. Different properties of the recorded peak are in good agreement with the theory indicating that square‐wave voltammetry could be treated as a potential tool for tensammetric studies of electroinactive surface active substances.

On reduction of the drug diflunisal in non-aqueous media

The electrochemical reduction of diflunisal was studied in dimethyl sulfoxide on static mercury drop electrode. Diflunisal yields one irreversible wave at −1.2 V (vs. Ag | AgCl | 1 M LiCl electrode) due to the reduction of the carboxylic functional group in the molecule. The electrochemical properties of the drug were compared with the ones of the chlorinated analogue. The study is based on cyclic voltammetry, tast polarography, and constant potential electrolysis. The experimental findings are supported by molecular orbital calculations. The mechanism of reduction of the carboxylic moiety was found to involve two electrons and two protons. The reduction pathway leads to formation of an aldehyde derivative.

Speciation of biochemically important iron complexes with amino acids: L-aspartic acid and L-aspartic acid - glycine mixture

Speciation of iron(III) (cFe=(0.5 - 40)×10−5mol dm−3) and indirectly of iron(II), in aqueous solution of L-aspartic acid and aspartic acid - glycine mixture was investigated by square-wave voltammetry on a static mercury drop electrode. A reversible, one-electron reduction process of iron(III)-aspartate complexes with peak potential between +0.04 and -0.17V was recorded, depending on the solution pH (4.5–8.6) and concentration of aspartic acid (cAsp=0.01 - 0.4mol dm−3). Cumulative stability constants of iron(III)-aspartate complexes: FeAsp+ (log K=13.16±0.01), FeAspOH0 (log β=20.76±0.02), FeAsp(OH)2− (log β=27.77±0.12) and Fe(Asp)2− (log β=17.62±0.10); and iron(II)-aspartate complexes: FeAsp0 (log K=4.17±0.11) and Fe(Asp)22− (log β=6.53±0.11), were determined at Ic=0.5mol dm−3 and 25±1°C. In the solution with mixture of amino acids, aspartic acid and glycine, a formation of mixed (Fe(III)-aspartate-glycine) complexes occurred. The reduction process was also shown to be reversible, so stability constants of mixed complexes (iron(III): FeAspGly0 (log β=17.35±0.02), FeAspGly(OH)− (log β=23.87±0.33), and iron(II): FeAspGly− (log β=6.83±0.23)) were calculated, as well.

Electrochemical Determination of Melamine on Static Mercury Drop Electrode and on Gold Nano Particle Modified Carbon Paste Electrode

An electrochemical method was developed for the determination of melamine (2,4,6 triamino- 1,3,5-triazine) on static mercury drop electrode (SMDE) and on gold nano particle modified carbon paste electrode. Interaction of melamine with Cu2﹢ ion was investigated and the decrease of Cu stripping peak was measured for the determination of melamine using SMDE. Oxidation property of melamine was improved using gold nano particle modified carbon paste electrode. Direct determination of melamine was proposed from the oxidation peak with three sigma detection limit of 0.43 μML﹣1. Recovery in milk powder sample has shown good recovery of melamine using the modified carbon paste electrode.

Theory of square wave voltammetry of amalgam forming ions at spherical electrodes

A theoretical model of reversible reduction of amalgam forming ion on stationary mercury drop electrode is developed for square wave voltammetry. The dependence of dimensionless net peak current on the dimensionless inverse electrode radius is investigated. This relationship is not linear, but it is a curve with two asymptotes. These results apply to electroanalytical measurements at spherical microelectrodes.

Quantifying Reduced Glutathione by Square-wave Voltammetry

This study examines the use of square wave voltammetry (SWV) to quantify reduced glutathione (GSH) dissolved in phosphate buffer (pH 7.5) using a static mercury drop electrode (working), Ag/AgCl electrode (standard) and a platinum wire (auxiliary). The applied voltage ranged from -0.7 to -0.2 V. Increasing concentrations of GSH (13-188 μmol/L) correlated with the voltammogram peak area (R2=0.99) and with the current at peak potential (Ip) (R=0.99). The reaction of GSH with diamide was monitored for validation of the method. Addition of increasing concentrations of diamide (13.3-50.8 μmol/L) to a fixed concentration of GSH (120 μmol/L) decreased the Ip, and the results obtained presented a relative deviation (RD) ≤ 14.5% (compared with expected concentrations by stoichiometry) for GSH concentrations above 33.8 μmol/L, whereas the spectrophotometric method (Elman’s reagent) presented RD ≤ 25.6%. These data indicate that SWV method is more accurate and presented equal precision (SD<8%) as compared to the commonly used spectrophotometric method. This method seems suitable for measuring GSH concentrations at room temperature and pH 7.5 (near biological conditions). Other advantages of this method that make it highly desirable for rapid diagnostic purposes include low cost, simplicity, sensitivity, rapid response and no prior sample preparation.

Electrochemical Behavior of Ni(II)-Salen at the Mercury Electrode

The complex Ni(II)-salen has been studied using cyclic and square-wave cathodic stripping voltammetry at the static mercury drop electrode in an aqueous media of phosphate and Hepes buffers (at pH 7.0). The resulting voltammograms consist of a totally irreversible one-electron transfer attributable to the coupling of Ni(II) salen/Ni(I) salen via an EC mechanism. The mean value for the transfer coefficientαin both supporting electrolytes was calculated as 0.35 ± 0.05. The amount of reactant adsorbed after 60 s of accumulation at −700 mV was calculated to be 2.8 × 10−8 mol·cm−2. The detection limit for nickel determination was found to be 3.4 × 10−9 mol L−1.

Trace and selective determination of cobalt(II) in water and salt samples using cathodic adsorptive stripping voltammetry in the presence of pyrogallol red

A sensitive and selective procedure is presented for voltammetric determination of cobalt. The procedure involves an adsorptive accumulation of cobalt pyrogallol red (PGR) complex on stationary mercury drop electrode, followed by cathodic stripping voltammetry measurement of reduction current of adsorbed complex at -1.17 V (vs. Ag/AgCl). The optimum conditions for determination of cobalt include pH 11.0, 35 ?M pyrogallol red, an accumulation potential of -0.9 V (vs. Ag/AgCl) and scan rate 80 mVs-1. The peak current is proportional to the concentration of cobalt over the concentration range of 5.0 to 280 ng mL-1 with a detection limit of 1 ng mL-1 with an accumulation time of 140 s. The method was applied for the determination of cobalt in analytical grade NaCl and water samples.