A Novel Voltammetric Method for the Determination of Maleic Acid Using Silver Amalgam Paste Electrode

An efficient voltammetric method was developed for the determination of maleic acid at a silver amalgam paste electrode (AgA‐PE) in Britton–Robinson buffer pH 2.0. The experimental parameters, such as pH of Britton–Robinson buffer, type of the supporting electrolyte and activation of the electrode surface were optimized. Under the optimal conditions, a linear response was observed over the 2×10^?6–1×10^?4 mol L^?1 maleic acid concentration range, determination limit being 5×10^?7 mol L^?1. A highly stable response, with a relative standard deviation (RSD) of 1.6% for 45 repetitive measurements of 1×10^?4 mol L^?1 maleic acid showed that there was no apparent surface passivation indicating the suitability of the method. The method was successfully applied for direct determination of maleic acid in drinking and river water.     

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.     

Voltammetric Determination of Acibenzolar‐S‐Methyl Using a Renewable Silver Amalgam Film Electrode

Acibenzolar‐S‐methyl (ASM) is a novel fungicide applied for crop protection. A renewable silver amalgam film electrode was used for the determination of ASM in pH 3.4 Britton? Robinson buffer using square wave adsorptive stripping voltammetry (SW AdSV). The parameters of the method were optimized. The electroanalytical procedure made possible to determine ASM in the concentration range of 5×10^?8–3×10^?7 mol L^?1 (LOD=4.86×10^?9, LOQ=1.62×10^?8 mol L^?1). The effect of common interfering pesticides and heavy metal ions was checked. The validated method was applied in ASM determination in spiked water samples.     

Electrodeposition of Silver Amalgam on Thin Gold Film Electrodes for Voltammetric Detection of 4‐Nitrophenol and DNA Labeled with Osmium Tetroxide‐Bipyridine Complex

Alternative electrode materials suitable to prepare novel working electrode applicable in detecting biopolymers such as nucleic acids, proteins or glycoproteins, represent a significant contribution to bio‐electroanalysis. Herein, electrodes made of vapor‐deposited thin gold films (vAuE) were used as an alternative substrate for the electrodeposition of silver amalgam particles (AgAPs), next to indium tin oxide and pyrolytic graphite, which are already used. The conditions and parameters of double pulse chronoamperometry were optimized for the most‐sensitive voltammetric detection of 4‐nitrophenol (4‐NP). The resulting electrodes were characterized by scanning electron microscope with energy dispersive X‐ray spectroscopy. While 4‐NP could not be detected by bare nonactivated vAuEs at all, their electrochemical activation offered a limit of detection (LoD) of 25 and 5 μmol.l^?1 by means of CV and DPV, respectively. AgAP electrodeposited on vAuE, offered 2.5‐times lower LoDs 10 μmol.l^?1 by CV and comparable LoD 5 μmol.l^?1 by DPV. Advantageously, AgAPs could be repeatedly deposited on and anodically dissolved from the vAuE with a relative standard deviation 13 % of the ten‐times repeated DPV signal of 4‐NP (100 μmol.l^?1). In comparison to vAuE, the vAuE‐AgAP offered about 400 mV broader potential window, which allowed detection of single strand DNA fragment labeled by osmium tetroxide?bipyridine complex down to 2 ng.μl^?1 by means of DPV.     

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.     

Renewable Silver‐Amalgam Film Electrode for Rapid Square‐Wave Voltammetric Determination of Thiamethoxam Insecticide in Selected Samples

The paper presents the use of a renewable silver‐amalgam film electrode (Hg(Ag)FE) for the determination of the insecticide thiamethoxam (TMO) in Britton‐Robinson buffer pH 7.0 (LOD=0.25 µg mL^?1, LOQ=0.70 µg mL^?1) by direct cathodic square‐wave voltammetry (SWV). The voltammetric response for TMO obtained at this electrode was the same as that obtained with a hanging mercury drop electrode, represented by two distinct reduction peaks. Since the electron transfer processes are coupled with chemical reactions involving protons, the SWV signals strongly depend on the pH of the supporting electrolyte. The developed Hg(Ag)FE‐SWV method was tested for the determination of TMO in spiked honey and river water samples, as well as for the determination of its content in the commercial formulation Actara 25 WG.     

Voltammetric Determination of Folic Acid Using a Graphite Paste Electrode

A simple differential pulse voltammetric method based on a graphite paste electrode (GPE) was developed for the quantitative determination of folic acid (FA) in tablets. The electrode exhibits a clear improvement of the current response. A linear response in the electroanalytical approach exists from 4.97×10^?6 to 2.94×10^?5 mol L^?1 with a limit of detection of about 2.67×10^?6 mol L^?1 in KCl solutions. The developed procedure was tested by recovery studies and compared with spectrophotometric and chromatographic methods. The results are described and discussed in the light of existing literature.     

Electrochemical Study of Moroxydine and its Voltammetric Determination with a Silver Amalgam Film Electrode

Moroxydine (Mor.) is an antiviral agent of biguanide structure. The paper presents a new silver amalgam film electrode (Hg(Ag)FE) for determination of Mor. in phosphate buffer, pH 6.2 (LOD=4×10^?9 mol L^?1, LOQ= 1×10^?8 mol L^?1) and in spiked urine using square wave adsorptive stripping voltammetry. It was found that the compound can act as an electrocatalyst not only at hanging mercury drop electrode but also at the Hg(Ag)FE. The electrode mechanism is connected with the hydrogen evolution reaction catalyzed by moroxydine. Adsorption of moroxydine at the mercury electrode was studied and special arrangements of molecules enabling electron transfer of the protonated form of moroxydine is suggested.     

Voltammetric Determination of Proguanil in Malarone and Spiked Urine with a Renewable Silver Amalgam Film Electrode

Electrochemical properties of proguanil were investigated by a voltammetric method (SWV) using a renewable silver amalgam film electrode. The influence of buffer pH as well as potential amplitude, frequency, and step potential was studied. The repeatability, precision and recovery of the developed method were examined. The reduction peak current was used for proguanil voltammetric determination in the range 1×10^?7–6×10^?6 mol L^?1, LOD=2.9×10^?8 mol L^?1, LOQ=9.7×10^?8 mol L^?1. The standard addition method was used to determine proguanil in a commercial formulation (Malarone) and in spiked urine.     

Voltammetric Determination of 8‐Nitroquinoline Using a Silver Solid Electrode and Its Application to Model Samples of Drinking and River Water

This work is focused on the application of a silver solid electrode (AgE) for the development of modern voltammetric methods for the determination of submicromolar concentrations of biologically active compounds present in the environment. 8‐Nitroquinoline (8‐NQ), a well‐known chemical carcinogen, was chosen as a model substance. Differential pulse voltammetry (DPV) was used to study electrochemical behavior of 8‐NQ in different aqueous matrices. The following optimal conditions for determination of 8‐NQ in the concentration ranges from 2 to 100 µmol L^?1 were used: Britton? Robinson (BR) buffer of pH 3.0, the regeneration potentials cycles (E_in=?1000 mV, E_fin=?100 mV) and constant cleaning potential ?2000 mV. Practical applicability of AgE for the determination of micromolar concentrations of 8‐NQ was verified on model samples of drinking and river water.     

Voltammetric Determination of Metronidazole Using a Sensor Based on Electropolymerization of α‐Cyclodextrin over a Carbon Paste Electrode

An electrochemical sensor for metronidazole (MTZ) was built via the surface modification of a carbon paste electrode (CPE) by a film obtained through electropolymerization of α‐cyclodextrin (CPE_α‐CD). The CPE_α‐CD was characterized by cyclic voltammetry (CV) and atomic force microscopy (AFM), by both techniques was demonstrated that the polymer film is coating the electrode surface. The electroreduction behaviour of MTZ in HClO₄ media as a supporting electrolyte was studied by differential‐pulse voltammetric (DPV) technique. The DPV electrochemical process was observed to be diffusion controlled and irreversible. Under optimal conditions, the peak current was proportional to MTZ concentration in the range of 0.5 to 103.0 μM with a detection limit of 0.28±0.02 μM. The method was successfully applied to quantify of MTZ in pharmaceutical formulations. In addition, this proposed MTZ sensor exhibited good reproducibility, long‐term stability and fast current response.     

Single-Sweep Voltammetric Determination of Tamoxifen at Carbon Paste Electrode

Abstract

A single-sweep voltammetric method was proposed for the determination of tamoxifen. The proposed method took advantage of both the accumulation of carbon paste electrode toward tamoxifen and the rapidity of single-sweep voltammetry. In HAc-NaAc (pH 4.1) buffer/methanol (85:15 v/v) mixed solution, an irreversible oxidation peak of tamoxifen was observed at 1.1 V (versus SCE). The second-order derivative peak current of tamoxifen and its concentration plots were rectilinear over the range of 7.0 × 10^?10 ～ 3.0 × 10^?8 mol · l^?1 with a detection limit of 1.0 × 10^?10 mol · l^?1 without any preconcentration. The proposed method was evaluated by analyzing tamoxifen citrate tablets, which was characterized by rapidity and higher sensitivity.     

掺杂硒修饰碳糊电极伏安法测定对乙酰氨基酚

采用循环伏安法制备了掺杂硒修饰碳糊电极,用循环伏安法和差分脉冲伏安法研究了对乙酰氨基酚在掺杂硒修饰碳糊电极上的电化学行为,建立了掺杂硒修饰碳糊电极测定对乙酰氨基酚的电化学方法。在pH 4.6的0.1mol·L-1乙酸-乙酸钠缓冲溶液中,对乙酰氨基酚在+0.61V呈现一个灵敏的氧化峰。对乙酰氨基酚的浓度在6.0×10-7~1.5×10-4 mol·L-1范围内与其氧化峰电流呈线性关系,检出限(3s/k)为2.8×10-7 mol·L-1。方法用于药品中对乙酰氨基酚的测定,测定结果与药典法测定值相符,测定值的相对标准偏差(n=5)在2.1%~2.5%之间。     

Sensitive Voltammetric Determination of Methyl Parathion Using a Carbon Paste Electrode Modified with Mesoporous Zirconia

A mesoporous zirconia modified carbon paste electrode was developed for electrochemical investigations of methyl parathion (MP, Phen‐NO₂). The significant increase of the peak currents and the improvement of the redox peak potential indicate that mesoporous zirconia facilitates the electronic transfer of MP. The oxidation peak current was proportional to the MP concentration in the range from 1.0×10⁻⁸ to 1.0×10⁻⁵ mol L⁻¹ with a detection limit of 4.6×10⁻⁹ mol L⁻¹ (S/N=3) after accumulation under open‐circuit for 210 s. The proposed method was successfully applied to the determination of MP in apple samples.     

Silver Amalgam Film Electrode of Prolonged Application in Stripping Chronopotentiometry

The utility of the cylindrical silver‐based mercury film electrode of prolonged analytical application in stripping chronopotentiometry (SCP) was examined. This electrode allowed us to obtain good reproducibility of results owing to the special electrode design, which enables regeneration of the thin layer before each measurement cycle. The accessible potential window in KNO₃ (pH 2), acetate and ammonia buffers was defined, and the optimal conditions (i.e., stripping current, deposition potential and deposition time) for the determination of Cd and Pb traces were selected. The detection limits, obtained for an accumulation time of 60 s, were 0.023 μg/L for Cd and 0.075 μg/L for Pb. The response increases linearly with Cd, Pb and Zn concentration, up to at least 100 μg/L. It was also shown that the proposed procedure ensures excellent separation of the In and Tl, Pb and Tl or the In and Cd signals. The method was tested with dolomite and lake sediment samples, and good agreement with reference values was achieved. The obtained results showed good reproducibility (RSD=5–6%) and reliability.     

Voltammetric Determination of Methimazole Using a Carbon Paste Electrode Modified with a Schiff Base Complex of Cobalt

The electrochemical behavior of methimazole, as an antithyroid agent, is investigated on the surface of a carbon‐paste electrode modified with a newly synthesized Schiff base complex of cobalt. The prepared modified electrode showed an efficient catalytic role in the electrochemical oxidation of methimazole, leading to remarkable decrease in oxidation overpotential and enhancement of the kinetics of the electrode reaction. The mechanism of the electrocatalytic process on the surface of the modified electrode is analyzed by obtaining the cyclic voltammograms in various potential sweep rates and pHs of the buffer solutions. The differential pulse voltammetry is applied as a very sensitive analytical method for the determination of sub‐micromolar amounts of methimazole. A linear dynamic range of 1×10^?6 to 1×10^?4 M with a detection limit of 5×10^?7 M is resulted for methimazole. The modified electrode is successfully applied for the accurate determination of methimazole in pharmaceutical and clinical preparations. The linear range in calibration curves remains constant in addition to tablet preparations of methimazole and also in spiking to the synthetic human serum samples. In comparison to calibration curves in background buffer solution, the slope of the curves showed a variation less than 3% in determinations in background solutions of tablet and human synthetic serum samples. These results showed high efficiency of the Voltammetric procedure for accurate determination of methimazole in drug and clinical preparations. The modified electrode can be prepared very easy and renewed in its surface by simple polishing. The reproducibility of the electrode response, based on ten measurements during two month, was 3.2% for the slope of the calibration curve.