Mariola Brycht

Conditioning of renewable silver amalgam film electrode for the characterization of clothianidin and its determination in selected samples by adsorptive square-wave voltammetry.

A new square-wave adsorptive stripping voltammetric (SWAdSV) method was developed for the determination of the neonicotinoid insecticide clothianidin (Clo), based on its reduction at a renewable silver amalgam film electrode (Hg(Ag)FE). The key point of the procedure is the pretreatment of the Hg(Ag)FE by applying the appropriate conditioning potential (-1.70 V vs. Ag/AgCl reference electrode). Under the optimized voltammetric conditions, such pretreatment resulted in the peak for the Clo reduction in Britton-Robinson buffer pH 9.0 at about -0.60 V, which was used for the analytical purpose. The developed SWAdSV procedure made it possible to determine Clo in the concentration range of 6.0×10(-7)-7.0×10(-6) mol L(-1) (LOD=1.8×10(-7) mol L(-1), LOQ=6.0×10(-7) mol L(-1)) and 7.0×10(-6)-4.0×10(-5) mol L(-1) (LOD=1.3×10(-6) mol L(-1), LOQ=4.2×10(-6) mol L(-1)). The repeatability, precision, and the recovery of the method were determined. The effect of common interfering pesticides was also investigated. Standard addition method was successfully applied and validated for the determination of Clo in spiked Warta River water, corn seeds samples, and in corn seeds samples treated with the commercial formulation PONCHO 600 FS.

The Influence of Protonation on the Electroreduction of Bi (III) Ions in Chlorates (VII) Solutions of Different Water Activity

We examined the electroreduction of Bi (III) ions in chlorate (VII) solutions under varied protonation conditions of the depolariser using voltammetric and impedance methods. The results of the kinetic parameter correlation lead to the statement that the changes in the amount of chloric (VII) acid against the amount of its sodium salt in the supporting electrolytes of the low water activity have a significant influence on the rate of Bi (III) ion electroreduction. The increase of the concentration of chloric acid sodium salt, as well as the chloric (VII) acid alone within the particular concentration of the supporting electrolyte, inhibits the process of Bi (III) ion electroreduction. It should be associated with the reorganisation of the structure of the double layer connected with the slow dehydration inhibited by ClO 4− ions. The standard rate constants ks values with the increase of the chlorate (VII) concentrations for all the solutions examined of chlorates (VII) confirms the catalytic influence of the decrease of water activity on the process of Bi (III) ion electroreduction. The multistage process is confirmed by the non-rectilinear 1nkf = f(E) dependences.

β–Cyclodextrins incorporated multi-walled carbon nanotubes modified electrode for the voltammetric determination of the pesticide dichlorophen

In this work, a glassy carbon electrode modified with β-cyclodextrins and multi-walled carbon nanotubes (β-CDs/MWCNTs/GCE) was constructed and applied for the square-wave adsorptive stripping voltammetric (SWAdSV) determination of the pesticide dichlorophen (Dcp). For the first time, this compound was electrochemically investigated. The voltammetric measurements were conducted in phosphate buffer (PBS) at pH 6.5 as a supporting electrolyte, and SWAdSV technique parameters were optimized. A linear calibration curve in the wide concentration range from 5.0 × 10-8molL-1 to 2.9 × 10-6molL-1 was obtained. Excellent analytical performance in terms of limit of detection (LOD) of 1.4 × 10-8molL-1 was achieved. The utility of the proposed method was verified by the quantitative analysis of Dcp in Pilica River water samples with satisfactory results. The characterization of modified electrodes was conducted by means of atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Moreover, in this work, the dissociation constants (pKa) of Dcp using potentiometric pH titration were estimated. The stoichiometry of the Dcp-β-CDs inclusion complex formed in solution was determined by proton nuclear magnetic resonance (1H NMR) spectroscopy, and a binding constant (β2) was estimated from NMR titration studies.

Voltammetric behaviour and quantitative determination of pesticide iminoctadine

Iminoctadine (IOD) was determined in spiked river water samples by square wave voltammetry (SWV) using a cyclic renewable silver amalgam film electrode (Hg(Ag)FE). It was found that the compound can act as an electrocatalyst. In Britton–Robinson buffer at pH 6.5 a signal connected with the catalytic hydrogen evolution reaction was detected at −1.8 V versus Ag/AgCl. Validation of the method was carried out. The LOD and LOQ have been estimated to be 2.6 × 10−9 mol L−1 and 8.5 × 10−9 mol L−1, respectively.

Electrochemical study of the fungicide acibenzolar-s-methyl and its voltammetric determination in environmental samples

The electrochemical behavior of new generation fungicide acibenzolar-s-methyl (S-methyl 1,2,3-benzothiadiazole-7-carbothioate, ASM) on the hanging mercury drop electrode (HMDE) was investigated using square wave adsorptive stripping voltammetry. This method of determination is based on the irreversible reduction of ASM at the HMDE. The well-defined ASM peak was observed at −0.4 V (vs. Ag/AgCl) in BR buffer at pH 2.2. The reduction peak current was proportional to concentration of ASM from 1.0 × 10−8 to 6.0 × 10−8 mol L−1 with detection and quantification limit 3.0 × 10−9 and 1.0 × 10−8 mol L−1, respectively. The applicability of the developed method for analysis of spiked samples of tap water, river water, and soil is illustrated. The effect of adsorption on the mercury electrode was studied in detail using the AC impedance method. Possible interferences with other common pesticides and heavy metal ions were examined. Clarification of the electrode mechanism was made using cyclic voltammetry (CV) technique.

Differential pulse voltammetric determination of an immunosuppressive drug teriflunomide on an edge plane pyrolytic graphite electrode

In the present work, sensitive and selective determination of teriflunomide (Trf) on an edge plane pyrolytic graphite electrode (EPPGE) using differential pulse voltammetry (DPV) is presented for the first time. It was found that Trf gives a single well-defined oxidation peak at ca. +1.0 V vs. Ag/AgCl (3 mol L−1 KCl) in Britton–Robinson buffer solution (BRBS) at pH 3.0. The optimization of pH and DPV parameters was performed. A linear response of Trf was obtained in the range of 2.5 × 10−6 to 5.0 × 10−5 mol L−1 for EPPGE. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 6.2 × 10−7 mol L−1 and 2.1 × 10−6 mol L−1, respectively. Furthermore, the proposed method was validated and successfully applied for the determination of Trf in the spiked samples of human urine with satisfactory recoveries in the range of 95.2–103.5% (RSD = 4.2%). The influence of potential interfering agents on the peak current response of Trf was also studied. Moreover, to understand the electrooxidation process of Trf on EPPGE, cyclic voltammetry (CV) was employed. Additionally, the surface topography and morphology of the EPPGE were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The surface area of EPPGE was calculated based on the Randles–Sevcik equation.

The effect of homocysteine and homocystine protonation on double-layer parameters at the electrode/chlorates(VII) interface:

In this study, a comparison of the properties of homocysteine and homocystine adsorption at mercury/chlorate(VII) interface was done. The adsorption of homocysteine and homocystine is in fact the adsorption of mercury(II) cysteine thiolate and mercury(I) cysteine thiolate. The differences in the capacity curves result probably from the formation of mercurous thiolate at the mercury surface. It seems that the changes in Ez and γ z values accompanying the change in the amino acid protonation in the basic electrolyte solution, confirm the altered arrangement of the cysteine mercury thiolates on the electrode surface.

Improved electroanalytical characteristics for the determination of pesticide metobromuron in the presence of nanomaterials

In the present work, bare ultra trace graphite electrode (UTGE), UTGE modified with multi-walled carbon nanotubes (UTGE-MWCNTs), and UTGE modified with graphene nanoplatelets (UTGE-GNPs) were considered as working electrodes. For the first time, the UTGEs were modified with MWCNTs and GNPs by simple and fast drop-casting approach (the whole procedures take no more times than ca. 30 min). The comprehensive microscopic and electrochemical characterization of the unmodified and the modified UTGEs was conducted by means of atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques. The prepared electrodes were further applied for the analytical purposes, and the procedures for the square-wave voltammetric (SWV) determination of pesticide metobromuron (Mbn) using the bare UTGE, the UTGE-MWCNTs, and the UTGE-GNPs were developed. For the first time, this compound was electrochemically investigated. The SWV measurements were performed in Britton-Robinson buffer (B-R) solution at pH 2.0 as a supporting electrolyte. SWV parameters, i.e. amplitude, frequency, and step potential, were optimized. The linear relationships between peak current vs. increasing concentrations of Mbn were defined using the bare UTGE, the UTGE-MWCNTs, and the UTGE-GNPs, and the limits of detection were calculated (0.13, 0.11, 0.048 μmol L-1, respectively). The analytical parameters determined from calibration curves indicate similar sensitivity on all tested electrodes, however, the widest linearity range as well as the lowest LOD and LOQ values were achieved on the UTGE modified with GNPs. The utility of the proposed method with the UTGE-GNPs was verified by the quantitative analysis of Mbn in soil samples with satisfactory results (recovery of 99.1%). Furthermore, the impact of possible interferences was tested and evaluated, and obtained results proved good selectivity of the proposed method.

First electrochemical study of the fungicide oxycarboxin

ABSTRACT In this article, the utility of a boron-doped diamond electrode for the determination of the fungicide oxycarboxin is demonstrated. For the first time, the square-wave voltammetry was employed in a quantitative determination of oxycarboxin on the boron-doped diamond electrode. It was found that oxycarboxin displays a well-expressed oxidation peak at a potential of ca. +1.5 V vs. Ag/AgCl in Britton–Robinson buffer with the maximum response in pH 4.0. As observed in cyclic voltammetry, oxycarboxin undergoes diffusion-controlled irreversible electrochemical oxidation. At optimised square-wave voltammetry parameters, the current response of oxycarboxin was linearly proportional to its concentration in the wide linear dynamic range of 8.0–100.0 μmol L−1 (2.1–26.7 mg L−1). The developed electroanalytical method yielded a relatively low limit of detection of 1.6 μmol L−1 (0.4 mg L−1), associated with high repeatability of the peak current expressed as relative standard deviation in the range of 1.1–2.9% for each concentration of oxycarboxin solution. This simple and sensitive method was proved to be suitable for an analysis of spiked river water samples with satisfactory results (relative standard deviation of 1.4%, recovery of 100.2%). The impact of possible interferences was tested and evaluated, and obtained results proved good selectivity of the proposed method. In addition, the influence of oxycarboxin on the corrosion properties of AISI 316 L stainless steel used as a construction material in farming was tested using potentiodynamic method, and a corrosive damage was characterised by means of scanning electron microscopy.