Mercury meniscus on solid silver amalgam electrode as a sensitive electrochemical sensor for tetrachlorvinphos

The in-house prepared mercury meniscus modified solid silver amalgam electrode (m-AgSAE) was successfully applied for the detection of organophosphate pesticide tetrachlorvinphos in pH 7 buffer solution. The electrochemical performance of m-AgSAE for the reduction of tetrachlorvinphos was evaluated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square wave voltammetry (SWV), respectively. The surface morphology of solid silver electrode (AgE), as-amalgamated solid silver amalgam electrode (AgSAE), and polished solid silver amalgam electrode (p-AgSAE) was examined by field emission scanning electron microscopy (FESEM). Among the applied techniques, DPV and SWV analysis showed a remarkable increase in the reduction peak current and provided a simple, fast, and sensitive method for the determination of tetrachlorvinphos. The electrochemical impedance spectroscopy (EIS) was used to correlate the electrocatalytic activity of AgSAE, p-AgSAE and m-AgSAE with their interfacial charge transport capabilities. Under the optimized experimental conditions, the DPV and SWV responses were linear over the 1–9 μM and 10–50 μM concentration ranges with a detection limit of 0.06 μM for DPV and 0.04 for SWV. The estimation of tetrachlorvinphos in the ground and waste water samples with the proposed method was in good agreement with that of the added amount. The proposed electrochemical method not only extends the application of non-toxic m-AgSAE, but also offers new possibilities for fast and sensitive analysis of tetrachlorvinphos and its structural analogs in environmental samples.     

Voltammetric Determination of 4‐Nitrophenol and 5‐Nitrobenzimidazole Using Different Types of Silver Solid Amalgam Electrodes – A Comparative Study

The voltammetric behavior of two genotoxic nitro compounds (4‐nitrophenol and 5‐nitrobenzimidazole) has been investigated using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at a polished silver solid amalgam electrode (p‐AgSAE), a mercury meniscus modified silver solid amalgam electrode (m‐AgSAE), and a mercury film modified silver solid amalgam electrode (MF‐AgSAE). The optimum conditions have been evaluated for their determination in Britton‐Robinson buffer solutions. The limit of quantification (L_Q) for 5‐nitrobenzimidazole at p‐AgSAE was 0.77 µmol L^?1 (DCV) and 0.47 µmol L^?1 (DPV), at m‐AgSAE it was 0.32 µmol L^?1 (DCV) and 0.16 µmol L^?1 (DPV), and at MF‐AgSAE it was 0.97 µmol L^?1 (DCV) and 0.70 µmol L^?1 (DPV). For 4‐nitrophenol at p‐AgSAE, L_Q was 0.37 µmol L^?1 (DCV) and 0.32 µmol L^?1 (DPV), at m‐AgSAE it was 0.14 µmol L^?1 (DCV) and 0.1 µmol L^?1 (DPV), and at MF‐AgSAE, it was 0.87 µmol L^?1 (DCV) and 0.37 µmol L^?1 (DPV). Thorough comparative studies have shown that m‐AgSAE is the best sensor for voltammetric determination of the two model genotoxic compounds because it gives the lowest L_Q, is easier to prepare, and its surface can be easily renewed both chemically (by new amalgamation) and/or electrochemically (by imposition of cleaning pulses). The practical applicability of the newly developed methods was verified on model samples of drinking water.     

Detecting DNA Damage with a Silver Solid Amalgam Electrode

Mercury electrodes modified with supercoiled (sc) DNA have been used as highly sensitive tools for the detection of DNA strand breaks or as sensors for DNA cleaving substances. In this paper we show that silver solid amalgam electrode (AgSAE), in connection with alternating current voltammetry, provides similar information about DNA damage as the hanging mercury drop electrode. The AgSAE can be used for the detection of enzymatic or chemical DNA cleavage in solution or at the electrode surface. AgSAE modified with scDNA can be utilized as a sensor for DNA nicking substances.     

Voltammetric Determination of Trace Amounts of 2‐Methyl‐4,6‐Dinitrophenol at a Silver Solid Amalgam Electrode

The voltammetric behavior of 2‐methyl‐4,6‐dinitrophenol was investigated by differential pulse voltammetry (DPV) at a nontoxic mercury meniscus‐modified silver solid amalgam electrode (m‐AgSAE). Conditions have been found for its determination by DPV at m‐AgSAE in the concentration range of 0.2 to 1 μmol L^?1.     

Voltammetric Determination of N,N‐Dimethyl‐4‐amine‐carboxyazobenzene at a Silver Solid Amalgam Electrode

The voltammetric behavior of N,N‐dimethyl‐4‐amino‐2′‐carboxyazobenzene was investigated by differential pulse voltammetry (DPV) at a mercury meniscus‐modified silver solid amalgam electrode (m‐AgSAE). Conditions have been found for its determination by DPV at m‐AgSAE in the concentration range of 0.4 to 15 μmol L^?1.     

Voltammetric Determination of Azidothymidine Using Silver Solid Amalgam Electrodes

A new simple and direct electroanalytical method was developed for the determination of azidothymidine in commercial pharmaceutical preparations. It is based on differential pulse voltammetry at silver solid amalgam electrode with polished surface (p‐AgSAE) or surface modified by mercury meniscus (m‐AgSAE). The electroreduction of azidothymidine in basic media at these electrodes gives rise to one irreversible cathodic peak. Its potential in 0.05 mol L^?1 borate buffer, pH 9.3 at ca. ?1050 mV is comparable to that using hanging mercury drop electrode (HMDE). Achieved limits of quantitation are in the 10^?7 mol L^?1 concentration range for both amalgam electrodes. According to the procedure based on the standard addition technique, the recoveries of known amounts of azidothymidine contained in pharmaceutical preparations available in capsules were 101.4±1.8% (m‐AgSAE), 100.3±3.5% (p‐AgSAE) and 102.0±1.0% (HMDE) (n=10). There was no significant difference between the values gained by proposed voltammetric methods and the HPLC‐UV recommended by the United States Pharmacopoeia regarding the mean values and standard deviations.     

Lactofen – Electrochemical Sensing and Interaction with dsDNA

The electrochemical reduction of lactofen (LCT) at the glassy carbon (GCE) and silver amalgam film electrode (AMFE) is investigatedin detail by the means of square wave voltammetry (SWV), square wave stripping voltammetry (SWSV) and cyclic voltammetry. The influence of various factors such as supporting electrolyte composition and SW parameters were studied. The AMFE electrode showed an excellent electrochemical activity toward the electro‐reduction of LCT, leading to a significant improvement in sensitivity as compared to the glassy carbon electrode.The SWSV detection limits for GCE and AMFE were 285.0 nM and 2.0 nM, respectively. The applicability of the developed voltammetric method for analysis of tap water and river water is illustrated with spiked samples analysis. Moreover, as lactofen is highly toxic to fish and other aquatic organisms, its interaction with dsDNA isolated from salmon sperm was tested. The intercalative mode of LCT binding to dsDNA was estimated. The heterogeneous rate constants were calculated for the free LCT and the LCT‐dsDNA complex. Moreover, LCT‐dsDNA complex binding ratio and equilibrium constant were determined. The decrease in the SWV peak current of LCT in the presence of dsDNA was used for the determination of dsDNA.     

Square Wave Stripping Voltammetry of Unlabeled Single‐ and Double‐Stranded DNAs

We show that, in difference to previously applied electrochemical methods working with stationary electrodes, square wave voltammetry produces well‐developed peaks II_SW (specific for dsDNA) and III_SW yielded by ssDNA at hanging mercury drop electrode (HMDE) and solid amalgam electrodes (SAEs). Using these peaks various kinds of DNA structural transitions can be studied, including unwinding of dsDNA at negatively charged electrode surfaces. The sensitivity of the DNA analysis is much better than that obtained with guanine oxidation signals at carbon electrodes. Both carbon electrodes and SAEs appear attractive as transducers in label‐free RNA and DNA sensors.     

Characterization and Use of Copper Solid Amalgam Electrode for Electroanalytical Determination of Triazines‐Based Herbicides

This paper reports the construction, characterization and use of copper solid amalgam electrode in the study of the electrochemical behavior of atrazine and ametryne herbicides by square‐wave voltammetry. This study was used as basis for the development of sensitive analytical methods for the determination of these herbicides in natural water, avoiding the use of mercury, by means of a solid electrode that presents high sensitivity and minimizes any environment contamination with mercury residues. The experimental and voltammetric conditions were evaluated and the results showed a reduction peak for atrazine at ?0.98 and at ?1.1 V vs. Ag/AgCl 3.0 mol L^?1 for ametryne, both with characteristic of an irreversible electrode reaction in an electrochemical diffusion controlled process, involving two electrons for each herbicide reduction. Based on voltammetric studies, it has been demonstrated that the most possible mechanism for the reduction of herbicides involved reduction of bond carbon‐chloride for atrazine and the reduction of bond carbon–SCH₃ for ametryne. The detection limit of herbicides obtained in pure water (laboratory samples) was shown to be lower than the maximum limit of residue established for natural water by the Brazilian Environmental Agency, demonstrating that this methodology is very suitable for determining any contamination by atrazine and ametryne residues in different samples, proving a good substitute for mercury electrodes.     

Reference Electrodes Based on Solid Amalgams

A reference saturated calomel electrode based on the non‐toxic silver solid amalgam (SCE‐AgSA) as a substitute for liquid mercury is described. Long‐term as well as short‐term tests made during a period of one year confirmed the SCE‐AgSA potential to be equal to that of SCE within the limits of ±1 mV (the difference ΔE_SCE‐AgSA=+1.08±0.24 mV (vs. SCE); SD=0.87; N=51). The voltammograms of four selected metal ions registered vs. SCE‐AgSA and vs. SCE could practically overlap each other. None of the mentioned electrodes were polarized to a significant degree even if the electric current applied reached 2 mA. On the basis of the obtained results the SCE‐AgSA could be considered as equivalent substitute for SCE. Owing to practically identical electrode potential of both types of the mentioned electrodes the results obtained using SCE‐AgSA are completely comparable to those measured vs. SCE, without any correction of peak potentials.     

Brdicka-type processes of cysteine and cysteine-containing peptides on silver amalgam electrodes

Silver solid amalgam electrode (AgSAE) was used for differential pulse voltammetric (DPV) measurements of cysteine and cysteine-containing peptides, glutathione, gamma-Glu-Cys-Gly and phytochelatin (gamma-Glu-Cys)(3)-Gly (PC3), in the presence of Co(II) ions. It had been established earlier that cysteine-containing peptides and proteins catalyze hydrogen evolution at mercury electrodes in presence of cobalt salts; these processes are known as the Brdicka reaction. DPV signals measured with the AgSAE, the surfaces of which had been modified by mercury meniscus or mercury film, were qualitatively the same as those obtained with the hanging mercury drop electrode (HMDE). With these electrodes the number and the intensity of Brdicka signals of cysteine, glutathione and PC3 differed, making a distinction among them possible. On the other hand, with the polished silver solid amalgam electrode (the surface of which was completely free of liquid mercury) all three compounds produced only one but strikingly intense peak in the region of Brdicka reaction. Using this signal, cysteine, glutathione as well as PC3 could be determined at 10(-8)M level, representing sensitivity up to 2 orders of magnitude better than attained with the mercury-modified AgSAEs or HMDE.     

Electrodes of Nontoxic Solid Amalgams for Electrochemical Measurements

The preparation, activation and electrochemical pretreatment of electrodes based on nontoxic solid amalgams were described. Testing of metal solid amalgam electrodes (MeSAEs) proved their broad applicability in many respects, e.g., as to the range of working potentials and the level of background currents, well comparable with those of the hanging mercury drop electrode (HMDE). A regeneration of their surfaces before each measurements could be simply automatized using a PC‐controlled system providing a reasonable repeatability of voltammetric measurements down to 3% RSD. Combination with stripping techniques at accumulation times t_ac=300 s the detection limit amounted to the concentration level of 1 ppb Cu(II), Pb(II), Cd(II), Zn(II), etc. Best electrochemical properties were exhibited by the silver solid amalgam electrode (AgSAE). For example, polished AgSAE (p‐AgSAE), completely free of liquid mercury, proved satisfactory even at more negative potentials enabling the determination of Zn(II), Mn(II), IO , etc. Moreover, even better repeatability of mercury meniscus modified AgSAE (m‐AgSAE) was due to better quality and renewability of its surface. In many cases further testing confirmed that under appropriate conditions MeSAEs represent good, often cheaper and more users‐friendly alternatives to HMDE.     

Utilization of a Copper Solid Amalgam Electrode for the Analytical Determination of Atrazine

A copper solid amalgam electrode was prepared and used for the voltammetric determination of atrazine in natural water samples by square wave voltammetry. This electrode is a convenient substitute for the hanging mercury electrode since it is selective, sensitive, reliable and inexpensive and presents low toxicity characteristic. The detection limit of atrazine obtained in pure water (laboratory samples) was shown to be lower than the maximum limit of residue established for natural water by the Brazilian Environmental Agency. The relative standard deviation for 10 different measurements was found to be only 3.98% in solutions containing 8.16×10^?6 mol L^?1 of atrazine. In polluted stream water samples, the recovery measurements were approximately 70.00%, sustaining the applicability of the proposed methodology to the analysis of atrazine in such matrices.     

Copper Solid Amalgam Electrodes

This work describes the behavior of copper solid amalgam electrodes (CuSAE). The applied potential range has been compared with that of the silver solid amalgam electrode (AgSAE) and the hanging mercury drop electrode (HMDE). In 0.05 M tetraborate buffer the applicable potential range of CuSAE is+0.945 V to ?1.75 V excluding ?0.2 V to ?0.5 V, where the anodic oxidation of copper occurs. CuSAE does not need other than electrochemical pre‐treatment, which has been documented by the evaluated repeatability of eleven voltammetric curves of Cd²⁺ (0.1 ppm), Pb²⁺ (0.1 ppm) and Mn²⁺ (0.5 ppm). The obtained results showed that CuSAE could substitute the solid copper, amalgamed copper or liquid copper amalgam electrodes, and can be applied for the study of systems needing an addition of Cu²⁺ ions into the measured solution.     

Determination of As(III) by anodic stripping voltammetry using a lateral gold electrode: experimental conditions, electron transfer and monitoring of electrode surface

The aim of this work is to evaluate the efficiency of the determination of As(III) by anodic stripping voltammetry (ASV) using a lateral gold electrode and to study the modifications of the electrode surface during use. Potential waveforms (differential pulse and square wave), potential scan parameters, deposition time, deposition potential and surface cleaning procedure were examined for they effect on arsenic peak intensity and shape. The best responses were obtained with differential pulse potential wave form and diluted 0.25 M HCl as supporting electrolyte. The repeatability, linearity, accuracy and detection limit of the procedure and the interferences of cations and anions in solution were evaluated. The applicability of the procedure for As(III) determination in drinking waters was tested. Cyclic voltammetry (CV) was used to study the electrochemical behaviour of As(III) and for the daily monitoring of electrode surface. Also scanning electron microscopy (SEM) analysis was used to control the electron surface. Finally we evaluated the possibility to apply the equations valid for flow systems also to a stirred system, in order to calculate the number of electrons transferred per molecule during the stripping step.     

A new voltammetric sensor for the determination of sulfite in water and wastewater using modified-multiwall carbon nanotubes paste electrode

The electrochemical response of a modified-carbon nanotubes paste electrode with p-aminophenol was investigated as an electrochemical sensor for sulfite determination. The electrochemical behaviour of sulfite was studied at the surface of the modified electrode in aqueous media using cyclic voltammetry and square wave voltammetry. It has been found that under the optimum condition (pH 7.0) in cyclic voltammetry, the oxidation of sulfite occurs at a potential about 680?mV less positive than that of an unmodified-carbon nanotubes paste electrode. Under the optimized conditions, the electrocatalytic peak current showed linear relationship with sulfite concentration in the range of 2.0?×?10^?7–2.8?×?10^?4?mol?L^?1 with a detection limit of 9.0?×?10^?8?mol?L^?1 sulfite. The relative standard deviations for ten successive assays of 1.0 and 50.0?µmol?L^?1 sulfite were 2.5% and 2.1%, respectively. Finally, the modified electrode was examined as a selective, simple and precise new electrochemical sensor for the determination of sulfite in water and wastewater samples.     

Voltammetric determination of phytochelatins using copper solid amalgam electrode

Voltammetric determination of synthetically prepared phytochelatins (γ-Glu-Cys)₂Gly (PC₂) and (γ-Glu-Cys)₃Gly (PC₃) has been studied using new type of copper solid amalgam electrode. The determination, based on the formation of cuprous complexes in buffer pH 8.1, is suitable for concentrations of PC in the range 10–100 nmol l⁻¹. Reproducibility, employing electrochemical cleaning of the electrode surface, was statistically evaluated. The achieved limit of detection (2.1–2.6×10⁻⁹ mol l⁻¹ for DCV measurement) together with the robust character of the electrode offer its use for detection of PCs in separated extracts of real samples.     

磺胺甲恶唑在二硫化钼纳米片修饰电极上的电化学行为

采用了研磨后超声和离心分离方法制备了二硫化钼纳米片,通过原子力显微镜(AFM)和扫描电子显微镜(SEM)对不同离心速度分离的二硫化钼纳米片进行了表征。使用循环伏安法(CV)和差分脉冲伏安法(DPV)在磺胺甲恶唑溶液中对二硫化钼纳米片修饰的玻碳电极进行了电化学行为研究。结果显示,磺胺甲恶唑在二硫化钼修饰电极的循环伏安图上有一对氧化还原峰。其峰电流值与扫描速度的平方根成正比,是扩散控制过程。DPV扫描结果显示,磺胺甲恶唑的峰电流与其浓度之间存在着明显的线性关系。研磨超声方法制备出的二硫化钼纳米片层材料在电极上能够加速电子的转移和传输,从而有效提高峰电流值,为进一步研制准确测定磺胺甲恶唑电化学传感器提供了一种可选择的材料和电化学分析方法。     

Highly Sensitive Determination of Tenofovir in Pharmaceutical Formulations and Patients Urine—Comparative Electroanalytical Studies Using Different Sensing Methods

This paper discusses the electrochemical behavior of antiviral drug Tenofovir (TFV) and its possible applicability towards electroanalytical determination with diverse detection strategies using square-wave voltammetry. Namely, oxidation processes were investigated using glassy carbon electrode with graphene oxide surface modification (GO/GCE), while the reduction processes, related to the studied analyte, were analyzed at a renewable silver amalgam electrode (Hg(Ag)FE). Scanning electron microscopy imaging confirmed the successful deposition of GO at the electrode surface. Catalytic properties of graphene oxide were exposed while being compared with those of bare GCE. The resultant modification of GCE with GO enhanced the electroactive surface area by 50% in comparison to the bare one. At both electrodes, i.e., GO/GCE and Hg(Ag)FE, the TFV response was used to examine and optimize the influence of square-wave excitation parameters, i.e., square wave frequency, step potential and amplitude, and supporting electrolyte composition and its pH. Broad selectivity studies were performed with miscellaneous interfering agents influence, including ascorbic acid, selected saccharides and aminoacids, metal ions, non-opioid analgesic metamizole, non-steroidal anti-inflammatory drug omeprazole, and several drugs used along with TFV treatment. The linear concentration range for TFV determination at GO/GCE and Hg(Ag)FE was found to be 0.3–30.0 µmol L^–1 and 0.5–7.0 µmol L^–1, respectively. The lowest LOD was calculated for GO/GCE and was equal to 48.6 nmol L^–1. The developed procedure was used to detect TFV in pharmaceutical formulations and patient urine samples and has referenced utilization in HPLC studies.     

A Highly Sensitive Method for Determination of Monobutyltin in Aqueous Media by Stripping Voltammetry at a Renewable Silver Amalgam Annular Band Electrode

An adsorptive stripping voltammetric (AdSV) procedure for the determination of monobutyltin in aqueous media at a silver liquid amalgam film‐modified silver solid amalgam annular band electrode (AgLAF? AgSAE) is described. Determination of monobutyltin proceeds in two steps. At the beginning monobutyltin ions (BuSn³⁺) are accumulated from 0.1 M NH₄NO₃ and 10 % ethanol solution at a potential of ?0.2 V, than the BuSn⁰ film is preconcentrated at the working electrode surface at a potential of ?0.7 V. After this step the DP AdSV voltammogram is recorded. The analytical parameters and the procedure of the electrode regeneration and activation were optimized. The calibration curve of monobutyltin in the range 0.02–0.30 mg L^?1 is linear (r=0.9973). The detection limit for 5 s of preconcentration, calculated as 3σ of the blank was equal to 0.004 mg L^?1, repeatability of the peak current was 1.8 % (n=5). Repeatability and sensitivity of monobutyltin determination depends strongly on the analyzed solution properties, measurement conditions and the working electrode quality. The proposed procedure was tested by means of monobutyltin determination in tap waters.