Search

The voltammetric characterisation and determination of insecticide flonicamid (N-cyanomethyl-4-(trifluoromethyl)nicotinamide) were performed for the first time using a simple electrochemical sensor, renewable silver-amalgam film electrode (Hg(Ag)FE). During the development of the direct cathodic square wave voltammetric method (SWV) for the determination of flonicamid, a voltammetric behaviour of a target analyte in aqueous Britton-Robinson buffer solution from pH 2.0 to pH 11.98 was examined. In the investigated pH range, the peak which appeared in the potential span between −0.86 V and −1.56 V vs. saturated calomel electrode depending on the applied pH value was chosen for analytical purposes. As optimal pH for the determination of flonicamid, pH 2.5 was selected. Cyclic voltammetric measurements at pH 2.5 confirmed that the electrode reaction mechanism is an irreversible reduction controlled by the diffusion of flonicamid at Hg(Ag)FE. The optimised Hg(Ag)FE-SWV method resulted in good linearity in the concentration range of 1.96–41.2 µg mL−1 while the relative standard deviation of the method was 0.30%. Flonicamid was successfully determined in commercial formulation Teppeki 500 WG® and spiked river water sample by the developed method using the standard addition procedure. The average value of flonicamid amount found in a commercial formulation based on three repetitions was 497.8 ± 0.9 g kg−1, which is in good agreement with the manufacturer's declaration (500 ± 25 g kg−1) and with comparative high-performance liquid chromatographic measurements with diode array detection where a found average value of flonicamid content was 497.5 ± 11.5 g kg−1. The obtained results also indicate that the developed SWV procedure using Hg(Ag)FE was appropriate for the determination of flonicamid in a spiked river water sample with the recovery of 92.86% and RSD of 6.19%. [ABSTRACT FROM AUTHOR]

Abstract: The present work describes the preparation of a simple, sensitive, and reliable H2O2 sensor made from carbon paste surface modified with a composite of platinum nanoparticles (< 5 nm) on graphitized carbon (Pt-C, 10% Pt on Vulcan XC72) by simply drop-coating. The unmodified carbon paste electrode (CPE) and the modified one (Pt-C/CPE) were characterized by scanning electron microscopy in combination with energy-dispersive X-ray spectrometry and by cyclic voltammetry. The Pt-C/CPE showed remarkable electrocatalytic properties toward the electrochemical redox reaction of H2O2 compared to CPE in phosphate (0.1 mol dm−3; pH 7.50) and acetate (0.1 mol dm−3; pH 4.50) buffer supporting electrolytes. Amperometry of H2O2 in the concentration range from 0.15 to 1.45 µg cm−3 with the Pt-C/CPE showed acceptable linearity, while the obtained values of LOQs were 0.06 µg cm−3 (pH 7.50, working potential 0.20 V, stirred solution) and 0.10 µg cm−3 (pH 4.50, working potential 0.50 V). The proposed analytical methods were applied to the determination of the H2O2 content in commercially available personal care products: disinfection (pH 7.50) and contact lens cleaning (pH 4.50) solutions. In both cases, obtained amperometric results are in good agreement with those measured by the traditional spectrophotometric method and with H2O2 concentration declared by producers. The Pt-C/CPE was also tested for monitoring of the H2O2 residual concentration in contact lens solution during its neutralization/decomposition process by solid Pt catalyst. At 6 h of neutralization treatment, 24.68 μg cm−3 of the H2O2 was determined which is below allowed H2O2 concentration concerning the limit of eye irritation.Graphical abstract: [ABSTRACT FROM AUTHOR]

Composite materials made of multiwalled carbon nanotubes and silver (Ag-MWCNT) or gold particles (Au-MWCNT) were synthesized and characterized by XRD and SEM/EDS techniques. The composites and the MWCNTs were applied as surface modifiers of carbon paste electrodes (CPEs). The mediator based electrocatalytic activity of the modified electrodes was investigated for H2O2 oxidation/reduction by electrochemical measurements. All voltammetric working electrodes (Ag-MWCNT/CPE, Au-MWCNT/CPE, MWCNT/CPE and the bare CPE) were characterized by cyclic voltammetry (CV) in acetate and phosphate supporting electrolytes (0.1 mol L−1, pH 4.50 and 7.50, respectively) in the absence and presence of the H2O2 analyte. Amperometric experiments were performed in stirred solutions at selected constant working potentials, in accordance with the CV responses, for developing new analytical methods for the determination of H2O2. In the case of the Ag-MWCNT/CPE the most promising working potentials in the acetate buffer solution were − 0.40 V and + 0.80 versus SCE; in phosphate buffer solution these values were between − 0.20 and − 0.30 V and from + 0.60 to + 1.0 V. The Au-MWCNT/CPE is applicable in acetate buffer supporting electrolyte in the working potential close to − 0.30 V versus SCE and from + 0.70 to + 1.0 V; in the phosphate buffer solution only from + 0.60 V versus SCE and higher values. Due to the presence of the signal enhancement effect of Au and Ag nanoparticles, the sensitivity of the obtained methods is significantly higher in comparison to the results obtained by the MWCNT/CPE and bare CPE. The relative standard deviation of the measurements was lower than 10%. The practical application using the Ag-MWCNT/CPE was shown for the determination of H2O2 in real nursing product sample. It was proven that the developed mediator based (electro)catalytic platform exhibits low detection limit, high selectivity, reproducibility and stability. [ABSTRACT FROM AUTHOR]

Composite materials made of multiwalled carbon nanotubes and silver (Ag-MWCNT) or gold particles (Au-MWCNT) were synthesized and characterized by XRD and SEM/EDS techniques. The composites and the MWCNTs were applied as surface modifiers of carbon paste electrodes (CPEs). The mediator based electrocatalytic activity of the modified electrodes was investigated for H2O2 oxidation/reduction by electrochemical measurements. All voltammetric working electrodes (Ag-MWCNT/CPE, Au-MWCNT/CPE, MWCNT/CPE and the bare CPE) were characterized by cyclic voltammetry (CV) in acetate and phosphate supporting electrolytes (0.1 mol L−1, pH 4.50 and 7.50, respectively) in the absence and presence of the H2O2 analyte. Amperometric experiments were performed in stirred solutions at selected constant working potentials, in accordance with the CV responses, for developing new analytical methods for the determination of H2O2. In the case of the Ag-MWCNT/CPE the most promising working potentials in the acetate buffer solution were − 0.40 V and + 0.80 versus SCE; in phosphate buffer solution these values were between − 0.20 and − 0.30 V and from + 0.60 to + 1.0 V. The Au-MWCNT/CPE is applicable in acetate buffer supporting electrolyte in the working potential close to − 0.30 V versus SCE and from + 0.70 to + 1.0 V; in the phosphate buffer solution only from + 0.60 V versus SCE and higher values. Due to the presence of the signal enhancement effect of Au and Ag nanoparticles, the sensitivity of the obtained methods is significantly higher in comparison to the results obtained by the MWCNT/CPE and bare CPE. The relative standard deviation of the measurements was lower than 10%. The practical application using the Ag-MWCNT/CPE was shown for the determination of H2O2 in real nursing product sample. It was proven that the developed mediator based (electro)catalytic platform exhibits low detection limit, high selectivity, reproducibility and stability. [ABSTRACT FROM AUTHOR]

Two types of bismuth modified electrodes, a bismuth-film modified glassy carbon (BiF-GCE) and a bismuth bulk modified carbon paste, were applied for the determination of selected nitroguanidine neonicotinoid insecticides. The method based on an ex situ prepared BiF-GCE operated in the differential pulse voltammetric (DPV) mode was applied to determine clothianidin in the concentration range from 2.5 to 23 μg cm-3 with a relative standard deviation (RSD) not exceeding 1.5%. The tricresyl phosphatebased carbon paste electrodes (TCP-CPEs), bulk modified with 5 and 20 w/w% of bismuth, showed a different analytical performance in the determination of imidacloprid, regarding the peak shape, potential window, and noise level. The TCP-CPE with 5% Bi was advantageous, and the developed DPV method based on it allowed the determination in the concentration range from 1.7 to 60 μg cm-3 with an RSD of 2.4%. To get a deeper insight into the morphology of the bismuth-based sensor surfaces, scanning electron microscopic measurements were performed of both the surface film and the bulk modified electrodes. [ABSTRACT FROM AUTHOR]

In this comparative study a traditional paraffin oil and graphite powder based carbon paste electrode (CPE) was surface modified with multiwalled carbon nanotubes (MWCNTs) and with composites of MnO 2 -MWCNT or Pt-MWCNT by drop coating method to prepare simply, sensitive and reliable voltammetric sensors either for the determination of H 2 O 2 or after additional modification of the appropriate sensor surfaces with glucose oxidase (GOx) for the determination of glucose via H 2 O 2 in selected samples. The scanning electron microscopic characterization in combination with energy dispersive X-ray spectrometry of the composite materials confirmed that the mediators, MnO 2 and Pt particles, are randomly distributed on the surface of the MWCNTs, and represent nearly 5% (m: m) of the composites expressed as Pt and Mn. Cyclic voltammetric (CV) investigations were performed in acetate (pH 4.50), phosphate (pH 7.50) and borate (pH 9.18) buffers to characterize the basic electrochemical behaviors and to select the working potentials suitable for hydrodynamic chronoamperometric (HA) determination of H 2 O 2 under different circumstances. The CV responses showed that in slightly alkaline media all investigated electrodes, i.e., CPEs unmodified and modified with plain MWCNTs and MWCNTs based composites are in principle applicable, but with different efficiency at different potentials, with favorable reduction and acceptable oxidation of H 2 O 2 at the Pt-MWCNT/CPE and predominately oxidation at the MnO 2 -MWCNT/CPE. The reproducibility of the responses with the MnO 2 -MWCNT/CPE is poor, but can be improved by electrochemical conditioning. The latter one performed well in alkaline supporting electrolyte (pH 9.18), while in the case of the Pt-MWCNT/CPE the signals are much better established in slightly acidic medium (pH 4.50). The analytical methods were optimized, mainly with the Pt-MWCNT/CPE as the preferential electrode, in terms of pH and working potential for the HA determination of H 2 O 2 in spiked milk samples including the development of an appropriate sample treatment procedure. This electrode was also used for the design of a very simple and reliable first generation oxidase biosensor for determination of glucose content in human infusion via its enzymatic reaction product H 2 O 2 . [ABSTRACT FROM AUTHOR]

A new, simple, and highly sensitive voltammetric method for the determination of low concentrations of a novel fungicide, fenoxanil ( Fen ), was developed using square wave voltammetry (SWV) and square wave adsorptive stripping voltammetry (SWAdSV) on a renewable silver amalgam film electrode (Hg(Ag)FE). The electrochemical reduction of Fen at the Hg(Ag)FE in Britton-Robinson (B-R) buffer at pH 6.8 was studied for the first time. The effect of the supporting electrolyte, pH, conditioning potential and conditioning time, frequency, amplitude, step potential, and accumulation potential and accumulation time were studied to select the optimum experimental conditions. The developed method can determine Fen in the concentration range of 5 × 10 −7 –4 × 10 −6 mol L −1 for SWV and 1 × 10 −10 –9 × 10 −10 mol L −1 for SWAdSV. Validation of the method was carried out. The method was successfully applied for trace level determination of Fen in spiked Warta River water and spiked rice samples by the standard addition method. The interference of common agents and metal ions was also examined. Fen adsorption at the mercury electrode was studied. [ABSTRACT FROM AUTHOR]