The use of copper solid amalgam electrodes for determination of the pesticide thiram

The complexes formed between copper and thiram and between mercury and thiram have been electrochemically (voltammetrically) investigated in the present work. Their structure was confirmed using electrospray ionization mass spectrometry. Due to formation of the complex between copper (from copper solid amalgam electrode) and thiram, the concentration of this pesticide can be determined. The voltammetric behavior of thiram was investigated at polished (p-CuSAE) and mercury meniscus modified (m-CuSAE) copper solid amalgam electrodes (inner diameter 1.5 mm) by differential pulse voltammetry (DPV) and by direct current voltammetry (DCV). Optimum conditions for DPV determination of thiram were found in Britton–Robinson buffer. The reaction mechanism was investigated using DCV and elimination voltammetry with linear scan. DPV with optimized parameters was applied for determination of thiram in analyzed solutions. The limits of detection were calculated as 16 nmol?L^?1 (t _acc?=?100 s) for m-CuSAE and 23 nmol?L^?1 (t _acc?=?60 s) for p-CuSAE. The proposed method was successfully applied for thiram determination in real sample solutions.     

Electrochemical behavior and voltammetric determination of the herbicide metribuzin at mercury electrodes

The electrochemical behavior of the herbicide metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one) at mercury electrodes was studied in aqueous solutions by direct current (DC) and tast polarography, differential pulse (DPV) and cyclic voltammetry (CV), and controlled-potential coulometry. The electrolysis products were separated and identified by chromatographic techniques combined with mass spectrometric detection. The reduction process in acid media includes two irreversible steps. In the first four-electron step the N-NH2 and the 1,6-azomethine bonds are reduced. The second step leads to the formation of 5-tert-butyl-2,3,4,5-tetrahydroimidazol-4-one at the mercury-pool electrode. The first reduction step combined with adsorptive accumulation of the herbicide molecule at the mercury electrode surface was used for its determination by differential pulse adsorptive stripping voltammetry (DPAdSV). Calibration curves were linear in the range 1-30 microg L(-1) with a detection limit of 0.27 microg L(-1) (1 nmol L(-1)) under the conditions used (buffer pH 4.5, Eacc = -0.45 V relative to Ag/AgCl and tacc = 10 s). Preconcentration on solid-phase extraction columns (SPE-phenyl) was used for the determination of very small amounts of metribuzin in river water samples. Recovery was approximately 97%. The reproducibility of the analytical procedure including SPE treatment and DPV determination was expressed as relative standard deviations of 2.53 and 3.66% for 2 and 6 microg L(-1) metribuzin, respectively.     

The Cyclic Renewable Mercury Film Silver Based Electrode for Determination of Uranium(VI) Traces Using Adsorptive Stripping Voltammetry

The new cyclic renewable mercury film silver based electrode (Hg(Ag)FE), applied for the determination of uranium(VI) traces using differential pulse adsorptive cathodic stripping voltammetry (DP AdCSV) is presented. The Hg(Ag)FE electrode with a surface area adjustable from 1.1 to 12 mm² is characterized by very good surface reproducibility (≤2%) and long‐term stability (more than 2 thousand measurement cycles). The mechanical refreshing of mercury film is realized in the simple constructed device, in a time shorter than 1–2 seconds. The effects of various factors such as: preconcentration potential and time, pulse height, step potential and supporting electrolyte composition are optimized. The calibration graph is linear from 0.4 nM (95 ng L^?1) to 250 nM (60 μg L^?1) for an accumulation time of t_acc=20 s, with correlation coefficient of 0.9996. For a Hg(Ag)FE with a surface area of 2.7 mm² the detection limit for an accumulation time of 120 s is as low as 12 ng L^?1. The repeatability of the method at a concentration level of the analyte as low as 2.4 μg L^?1, expressed as RSD is 2.5% (n=7). The proposed method was successfully applied and validated by studying the recovery of U(VI) from spiked river water and sediment samples.     

Direct Electrochemical Determination of Glyphosate at Copper Phthalocyanine/Multiwalled Carbon Nanotube Film Electrodes

A copper phthalocyanine/multiwalled carbon nanotube film‐modified glassy carbon electrode has been used for the determination of the herbicide glyphosate (Gly) at ?50 mV vs. SCE by electrochemical oxidation using differential pulse voltammetry (DPV). Cyclic voltammetry and electrochemical impedance spectroscopy showed that Gly is adsorbed on the metallic centre of the copper phthalocyanine molecule, with formation of Gly‐copper ion complexes. An analytical method was developed using DPV in pH 7.4 phosphate buffer solution, without any pretreatment steps: Gly was determined in the concentration range of 0.83–9.90 μmol L^?1, with detection limit 12.2 nmol L^?1 (2.02 μg L^?1).     

Development of Electroanalytical Methods Using Different Electrodes for the Determination of Progesterone (P4) in Pharmaceutical Formulations and Human,Cow and Goat Milk

For the determination of progesterone (P4) electroanalytical studies were performed using mercury electrode (HMDE) and screen-printed boron-doped diamond electrode (BDD-SPE). The effects of pH, supporting electrolyte, accumulation potential and time (E_acc, t_acc) were studied in both systems. The optimum conditions were: i) HMDE: pH 7,0; E_acc: −0,1 V and t_acc: 40 s, ii) BDD-SPE: 0,5 mol L⁻¹ H₂SO₄; E_acc: 0,0 V and t_acc: 120 s. Under these conditions, the detection limit was 3.1 μg L⁻¹ for HMDE and 45.6 μg L⁻¹ for BDD-SPE. Both methods were validated and applied in the P4 determination on pharmaceutical formulations and milk samples.     

Determination of lead in the presence of morin-5′-sulfonic acid and sodium dodecyl sulfate by adsorptive stripping voltammetry

A simple and sensitive electroanalytical method is developed for the determination of lead by adsorptive stripping voltammetry (AdSV) in the presence of morin-5′-sulfonic acid (MSA) and sodium dodecyl sulfate (SDS). The Pb-MSA complex accumulates on the surface of a hanging mercury drop electrode (HMDE) and peak current is measured by square wave voltammetry (SWV). The complex is reduced at −0.48 V and peak current increases when low concentrations of SDS are added to the sample solution. The experimental variables pH, MSA concentration (C_MSA); accumulation time (t_acc); accumulation potential (E_acc), and SDS concentration (C_SDS), as well as potential interferences, are investigated. Under the optimized conditions (pH 3.2; C_MSA: 0.5 μmol L⁻¹; t_acc: 60 s; E_acc: −0.35 V, and C_SDS: 20 μmol L⁻¹), peak current is proportional to the concentration of Pb(II) over the 0.1-32.0 μg L⁻¹ range, with a detection limit of 0.04 μg L⁻¹. The relative standard deviation for a solution containing 5.0 μg L⁻¹ of Pb(II) solution was 1.5% for seven successive assays. The method was validated by determining Pb(II) in synthetic sea water (ASTM D665) spiked with ICP multi-element standard solution and in certified reference water (GBW08607). Finally, the method was successfully applied to the determination of Pb(II) in tap water and sea water after UV digestion.     

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.     

Electrochemical behaviour and determination of rimsulfuron herbicide by square wave voltammetry

The voltammeric behaviour of rimsulfuron herbicide has been studied by square wave stripping voltammetry on static hanging mercury drop electrode. It exhibited a well-defined peak within the pH range of 1.0–6.0, having a maximum peak response at ?600 mV (vs.Ag/AgCl) at pH 3.0. The factors such as accumulation potential (E_acc), accumulation time (t_acc), frequency (f), pulse amplitude (ΔE) and step potential (ΔE_s) have been optimised. The calibration plot was a straight line in the range of 4.4–134.4 μg L^?1 with a detection limit of 1.3 μg L^?1. The validity of the method was assessed from the recoveries of spiked lake water, tomato juice and agrochemical formulation of Doncep^®. The results of the experiments conducted for five recoveries were 48.8 ± 1.7 and 49.7 ± 1.0 μg L^?1, which are very close to the rimsulfuron spiked to lake water and tomato juice (50 μg L^?1), with a relative error of –2.4% and ?0.6%, respectively. The electrode reaction mechanism was also postulated.     

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 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.     

Electrochemical determination of carbaryl oxidation in natural water and soil samples

An electrochemical method for the determination of carbaryl, after prior oxidation to 1,4-naphthoquinone in natural water and soils is reported. The coulometric oxidation of carbaryl at a platinum electrode was studied using 0.024 mol/L Britton-Robinson buffer (pH 7.0). The reduction of the oxidation product 1,4-naphthoquinone at a dropping mercury electrode was used for the indirect determination of carbaryl after separation on C₁₈ Sep-pak cartridges by differential pulse polarography (detection limits: 0.41 mg L^?1 of water and 0.47 mg kg^?1 of soil) and directly without separation by adsorptive stripping voltammetry (detection limits: 5 μg L^?1 of water and 7 μg kg^?1 of soil, for 75 s preconcentration time). Relative errors were lower than 3.7% and relative standard deviations smaller than 4.5%.     

Simultaneous Determination of Rosmarinic Acid and Protocatechuic Acid at Poly(o‐Phenylenediamine)/Pt Nanoparticles Modified Glassy Carbon Electrode

A system of Pt nanoparticles and poly(ortho‐phenylenediamine) film electrochemically deposited onto a glassy carbon electrode (GCE/PoPD/Pt) was fabricated. Scanning electron microscopy, Fourier‐transform infrared spectroscopy, and atomic force microscopy techniques were used to identify the surface characteristics of the composite electrode. The conductive polymers and Pt nanoparticles together resulted in a synergistic effect, and the new formed surface was highly active against polyphenolic structures. Rosmarinic acid (RA) and protocatechuic acid (PCA) are phenolic compounds found in plants, and they are used in many applications, particularly as pharmaceuticals. The GCE/PoPD/Pt was used for the simultaneous determination of RA and PCA in a pH 2.0 H₂SO₄ solution for the first time. The RA and PCA concentrations were determined using differential pulse voltammetry (DPV) and chronoamperometry. By the amperometry measurement, for RA and PCA, a linear relation was observed in the concentration ranges of 1–55 μmol L^?1 and 1–60 μmol L^?1, with detection limits of 0.5 μmol L^?1 and 0.6 μmol L^?1, respectively. In the simultaneous determination with DPV, the detection limits for both RA and PCA were calculated as 0.7 μmol L^?1. The GCE/PoPD/Pt was successfully used for the simultaneous determination of RA and PCA in a real sample, and its accuracy was verified by high‐performance liquid chromatography studies.     

Renewable Copper and Silver Amalgam Film Electrodes of Prolonged Application for the Determination of Elemental Sulfur Using Stripping Voltammetry

New, renewable copper (Hg(Cu)FE) and silver (Hg(Ag)FE) based amalgam film electrodes applied for the determination of elemental sulfur using differential pulse cathodic stripping voltammetry are presented. With surface areas adjustable from 1 to 12 mm², both electrodes are characterized by very good surface reproducibility (≤2%) and long‐term stability (a few thousand measurement cycles). The mechanical refreshing of the amalgam film takes about 1–2 seconds. The effects of various factors such as instrumental parameters and the supporting electrolyte composition were optimized. Interferences from sulfides are easily removed by the addition of acid, and bubbling with argon, for Hg(Ag)FE. In the case of Hg(Cu)FE, sulfides did not interfere. The calibration graph is linear within the studied range from 16 ng L^?1 to 4.8 μg L^?1 for Hg(Cu)FE, and up to 6.4 μg L^?1 for Hg(Ag)FE (t_acc=15 s). The correlation coefficients for the two electrodes were at least 0.997. The detection limits for a low concentration of S(0) and t_acc=60 s are as low as 14 ng L^?1 for Hg(Cu)FE and 4 ng L^?1 for Hg(Ag)FE. The proposed method was successfully applied and validated by studying the recovery of S(0) from spiked river water.     

Voltammetry as the First Method for Direct Determination of a Novel Antagonist of A2A Adenosine Receptors

In this article, for the first time, the analytical method for determination of a novel antagonist of A_2A adenosine receptors (8‐(4‐methoxyphenyl)‐4‐oxo‐4,6,7,8‐tetrahydroimidazo[2,1‐c][1,2,4]triazine‐3‐carbohydrazide, namely IMT), which can be used as a drug for liver diseases, was presented. For this purpose a commercially available boron‐doped diamond electrode (BDDE) in combination with differential pulse voltammetry (DPV) was applied. It was found by cyclic voltammetry (CV) that IMT displays at BDDE, as a sensor, two well‐defined oxidation peaks at potentials of 0.81 and 1.18 V and one reduction peak at 1.1 V vs. Ag/AgCl in 0.1 mol L^?1 acetate buffer (pH 4.5±0.1). The oxidation and reduction mechanism of IMT was proposed. The developed DPV method allowed the successful determination of IMT in the range of 0.05–50 μmol L^?1 with detection limit equal to 0.0094 μmol L^?1 and without any chemical modifications and electrochemical pretreatment of the electrode surface. The proposed procedure allows the determination of IMT in vitro directly from urine samples.     

Redox Speciation of Inorganic Arsenic in Water and Saline Samples by Adsorptive Cathodic Stripping Voltammetry in the Presence of Sodium Diethyl Dithiocarbamate

This paper describes a new voltammetric procedure for the inorganic speciation of As(III) and As(V) in water samples. The procedure is based on the chemical reduction of arsenate [As(V)] to arsenite [As(III)] followed by the voltammetric determination of total arsenic as As(III) at the hanging mercury drop electrode (HMDE) by adsorptive cathodic stripping voltammetry (AdCSV) in the presence of sodium diethyl dithiocarbamate (SDDC). The reduction step involved the reaction with a mixture of Na₂S₂O₅ and Na₂S₂O₃ in the concentrations 2.5 and 0.5 mg mL^?1, respectively, and the sample heating at 80 °C for 45 min. The linear range for the determination of total arsenic as As(III) in the presence of SDDC was between 5 and 150 μg L^?1 for a deposition time of 60 s (r=0.992). A detection limit of 1.05 μg L^?1 for total As was calculated for the method in water samples using a deposition time of 60 s. The detection limits of 4.2 μg L^?1 and 15.0 μg L^?1 for total As in seawater and dialysis concentrates, respectively, were calculated using a deposition time of 60 s. The relative standard deviations calculated were 2.5 and 4.0% for five measurements of 20 μg L^?1 As(V) as As(III) in water and dialysis concentrates, respectively, after chemical reduction under optimized conditions. The method was applied for the determination of As(III) and total As in samples of dialysis water, mineral water, seawater and dialysis concentrates. Recovery values between 86.0 and 104.0% for As(III) and As(V) added to the samples prove the satisfactory accuracy and applicability of the procedure for the arsenic monitoring.     

Electrode Modified with Langmuir–Blodgett (LB) Film of Calixarenes for Preconcentration and Stripping Analysis of Hg(II)

A new type of current sensor, Langmuir–Blodgett (LB) film of calixarene on the surface of glassy carbon electrode (GCE) was prepared for determination of mercury by anodic stripping voltammetry (ASV). An anodic stripping peak was obtained at 0.15 V (vs. SCE) by scanning the potential from ?0.6 to +0.6 V. Compared with a bare GCE, the LB film coated electrode greatly improves the sensitivity of measuring mercury ion. The fabricated electrode in a 0.1 M H₂SO₄+0.01 M HCl solution shows a linear voltammetric response in the range of 0.07–40 μg L^?1 and detection limit of 0.04 μg L^?1 (ca. 2×10^?10 M). The high sensitivity, selectivity, and stability of this LB film modified electrode demonstrates its practical application for a simple, rapid and economical determination of Hg²⁺ in a water sample.     

Fabrication of a nanostructure-based electrochemical sensor for simultaneous determination of N-acetylcysteine and acetaminophen

A carbon-paste electrode modified with 2,7-bis(ferrocenyl ethyl)fluoren-9-one (2,7-BF) and carbon nanotubes (CNTs) was used for the sensitive and selective voltammetric determination of N-acetylcysteine (NAC). The mediated oxidation of NAC at the modified electrode was investigated by cyclic voltammetry (CV). Also, the values of catalytic rate constant (k), and diffusion coefficient (D) for NAC were calculated. Differential pulse voltammetry (DPV) of NAC at the modified electrode exhibited two linear dynamic ranges with a detection limit (3σ) of 52.0 nmol L⁻¹. DPV was used for simultaneous determination of NAC and acetaminophen (AC) at the modified electrode, and quantitation of NAC and AC in some real samples by the standard addition method.     

Simultaneous Determination of Nickel and Cadmium by Adsorptive Stripping Voltammetry

A sensitive and fast method for the simultaneous determination of trace amounts of nickel and cadmium in real samples has been described using differential pulse adsorptive stripping voltammetry (DPASV) by adsorptive accumulation of the N,N′‐bis(salicylaldehydo)4‐carboxyphenylenediamine (BSCPDA)–complex on the hanging mercury drop electrode (HMDE). As supporting electrolyte 0.02 mol L^?1 ammonia buffers containing ligand has been used. Optimal analytical conditions were found to be: BSCPDA concentration of 42 μM, pH 9.6 and adsorption potential at ?50 mV versus Ag/AgCl. With an accumulation time of 20 s, the peaks current are proportional to the concentration of nickel and cadmium over the 1–180, and 0.5–200 ng mL^?1 with detection limits of 0.06 and 0.03 ng mL^?1 respectively. The sensitivity of method for determination of nickel and cadmium were obtained 0.54 and 0.98 nA mL ng^?1, respectively. The procedure was applied to simultaneous determination of nickel and cadmium in some real and synthetic artificial samples with satisfactory results.     

Square-wave adsorptive stripping voltammetric determination of antihypertensive agent telmisartan in tablets and its application to human plasma

The adsorptive stripping voltammetry of telmisartan was investigated with a hanging mercury drop electrode. This compound produced a catalytic hydrogen wave at ?1.5 V in Britton Robinson buffer of pH 10.38, and the peak current increased with adsorptive accumulation at the electrode. Adsorptive stripping voltammetry with the catalytic hydrogen wave could provide a sensitive novel method for the determination of telmisartan. Various chemical and instrumental parameters affecting the monitored electroanalytical response were investigated and optimized for telmisartan determination. Under these optimized conditions the square-wave adsorptive stripping voltammetric (SW-AdSV) peak current showed a linear dependence on drug concentration over the range 0.05–3.00 μg/mL (1 × 10^?7?6 × 10^?6 M) (r = 0.999) with accumulation for 120 s at ?1.0 V vs. Ag/AgCl. The proposed electrochemical procedure was successfully applied for the determination of telmisartan in pharmaceutical tablets and human plasma. The results of the developed SW-AdSV method were comparable with those obtained by reported analytical procedures.     

Voltammetric Determination of Cymoxanil and Famoxadone at Different Types of Carbon Electrodes

Differential pulse voltammetry (DPV) at a carbon fibre rod electrode (CFRE) and a capillary carbon paste electrode (CPE) have been used for the determination of pesticides cymoxanil and famoxadone, respectively. In the cathodic potential range, optimum conditions were found for the determination of cymoxanil by DPV at CFRE at pH 4 with limit of quantification (L_Q) of 5.9×10^?7 mol L^?1. In the anodic area, determination of famoxadone by DPV at CPE was performed at optimum pH 2 with L_Q=1.4×10^?7 mol L^?1. Practical applicability of the newly developed methods was verified on spiked samples of river water and soil.