Pb(II) Determination in a Single Drop Using a Modified Screen-Printed Electrode

This work presents the development and validation of an electroanalytical method for Pb(II) determination in a single drop. The electrochemical sensors used were an unmodified screen-printed electrode (SPE) and a Bi-film SPE (BiFSPE). Anodic square wave stripping voltammetry (SWASV) was performed at an accumulation potential of −1.5 V vs. Ag/AgCl and an accumulation time of 60 s. Electroanalysis with an unmodified SPE did not yield satisfactory results, whereas the BiFSPE was a much better analysis method. The linear concentration using the BiFSPE was in the range of 138.8–162.5 µg/L. The accuracy and precision were evaluated for different spiked concentrations, but the method using the unmodified SPE was neither accurate nor precise. Using the BiFSPE, the method was found to be both accurate and precise for Pb(II) determination at a concentration of 140.0 μg/L, with recovery and relative standard deviation (RSD) of 106.6% and 12.1%, respectively. In addition, using the BiFSPE, LOD and LOQ values of 1.2 μg/L and 3.3 μg/L were obtained, respectively. The possible interference effect on Pb(II) stripping signal was checked in the presence of Cd(II), Zn(II), Cu(II), Sn(IV), Sb(III), Hg(II), Fe(III), As(V), K(I), I−, Ca(II), and NO3−. Electrochemical impedance spectroscopy measurements were also performed for the unmodified SPE and BiFSPE. The application of single drop Pb(II) analysis was tested by real water sample analysis.

Copper Amalgam Working Electrode for Voltammetric Determination of Selenite

Selenium is one of the heavy metal pollutants in the aquatic environment. Selenite is a form of inorganic selenium, which is very poisonous to living things. Therefore, we need a method that selectively identify selenite to determine its concentration in water. In this study, a square wave stripping voltammetry was used to measure selenite concentration using copper amalgam working electrode. The optimum measurement parameters were obtained at a deposition potential of –450 mV and a deposition time of 800 seconds. This analysis method had good precision with a relative standard deviation (% RSD) of 4.89%. Linear calibration curves are shown in the range 0.03 mM – 0.10 mM with R2 of 0.988 and in the range of 0.10 mM – 0.70 mM with R2 of 0.995 and a detection limit of 9.0 µM. The standard selenite solution was measured with a recovery percentage of 96.67%. The same solution was measured using the HG-AAS method and the recovery percentage was 96.35%. Statistical tests using the t-test showed that the two results did not have a significant difference with a 95% confidence limit. Thus, the voltammetry method using copper amalgam working electrode can be used as an alternative method for determining selenite, as it is cheaper and simpler than the HG-AAS method.

Implanted Bioelectric Neuro Assay with Sensing Interface Circuit

Neuromolecular glucose and dopamine assays were searched using a DNA immobilized onto a carbon nanotube paste electrode (PE). The analytical molecular detection limits of 0.13 ugL–1(6.855 × 10–10 M) Dopamine and 1.9 ugL–1 (1.06 × 10–8 M) glucose were attained using square wave stripping voltammetry. A handmade three-electrode system was implanted in the nerve network of a fish backbone, and two working electrodes were implanted in left and right pinna muscles. These were interfaced with a neuron electrochemical workstation and a nerve machine sensing circuit. This interface could be obtained for the psychological function and other body functions. The interfaced circuit could be controlled with a machine system. The results are useful in machine brain intercontrol systems.

Electrochemical Behavior and Square-Wave Stripping Voltammetric Determination of Roflumilast in Pharmaceutical Dosage Forms

Background: Bronchial asthma and chronic obstructive pulmonary disease (COPD) are among the most common chronic diseases. Roflumilast is a novel, potent, selective, and long-acting phosphodiesterase 4 (PDE-4) inhibitor for the treatment of bronchial asthma and COPD. It has anti-inflammatory effects and it has been shown to reduce exacerbations and improve pulmonary function in patients with COPD. Although there have been some other analytical methodologies reported for the determination of roflumilast in pharmaceutical dosage forms, there has not yet been any electrochemical methodology proposed for determination of this unique active pharmaceutical ingredient in its dosage forms. Methods: The proposed method was based on electrochemical reduction of roflumilast at a hanging mercury drop electrode (HMDE) in 0.1 M K2HPO4 and 0.1 M Na2B4O7 (1:1, v/v) buffer at pH 5.0. Two reduction peaks were observed at -1150 mV and -1260 mV with 30 s of accumulation time and -850 mV of accumulation potential time versus Ag/AgCl reference electrode. Results: The highest peak current values with the best peak definition were observed at a frequency of 50 Hz, scan increment of 5 mV, and pulse amplitude 25 mV. The proposed method was validated by evaluating validation parameters such as linearity, sensitivity, repeatability, accuracy, precision, selectivity, recovery, robustness, and ruggedness. A good linear correlation (r=0.9948) was obtained between the electrochemical response of roflumilast and its concentration in the range of 0.74-3.05 µg mL-1 under the optimum conditions. The obtained accuracy results were between 2.04% and -2.04% while the relative standard deviation of the results was at least 2.78% for intra-day and inter-day studies. Mean recovery for the real applications was 100.63% ± 0.52%. The electrochemical behavior of roflumilast was investigated by cyclic voltammetry. The cyclic voltammogram of roflumilast exhibited two peaks and the reduction reaction was reversible. Conclusion: This developed and validated SWSV method was applied successfully for the determination of roflumilast in tablet dosage form (Daxas) to assess active roflumilast content. Since high-performance liquid chromatography is a dominant technique in industry for quality control of active pharmaceutical ingredients, the finding in the present study demonstrated that square-wave stripping voltammetry could be easily utilized in routine applications to determine roflumilast content in its dosage forms.

Antimicriobial Activity of Silver-Nanoparticles studied by Scanning Probe Microscopy

<p>Biofilms are well-organized sessile communities which exhibit an increased tolerance against antimicrobial and antibiotic treatments in comparison with their planktonic counterparts. Biofilms are ubiquitous and due to their high resilience, the problem with contamination of medical implants leads to serious health problems [1]. Within the last decades, novel therapies to prevent the formation of biofilms have been developed and, among others, antimicrobials based on metal nanoparticles (NPs) have been intensively studied [2], due to their ability to reduce biofilm formation. Silver nanoparticles (AgNPs) are known to be effective antimicrobial agents, as silver(I) has the ability to penetrate the cell and produce oxidative stress via the generation of reactive oxygen species (ROS) [3]. To understand the release mechanism of silver(I) ions, scanning electrochemical probe microscopy such as scanning electrochemical microscopy (SECM) is highly suitable.</p> <p>In this contribution, biocompatible AgNPs-fluoropolymer (Ag-CF<sub>x</sub>) composite films, prepared by ion beam sputtering (IBS) deposition [4], are investigated in respect to silver(I) release associated to the swelling of the antimicrobial film. The mechanism of the silver(I) release is studied real-time by scanning electrochemical microscopy (SECM) in combination with square-wave stripping voltammetry and the relation between controlled silver(I) release and the swelling of Ag-CF<sub>x</sub> films will be presented, combining electrochemical techniques and atomic force microscopy (AFM).</p> <p> </p> <p>References</p> <p>[1] G.C. Anderson, et al. Innate and Induced Resistance Mechanisms of Bacterial Biofilms. In Bacterial Biofilms; Romeo, T., Ed.; Springer Berlin Heidelberg: Berlin, Heidelberg, <strong>2008</strong>; pp 85–105.</p> <p>[2] M.C. Sportelli, et al. Nano-Antimicrobials Based on Metals. In Novel Antimicrobial Agents and Strategies; John Wiley & Sons, Ltd, <strong>2014</strong>; pp 181–218.</p> <p>[3] N. Durán, et al. Nanomedicine, <strong>2016</strong>, 12(3), 789-799.</p> <p>[4] M.C. Sportelli, et al. <strong>Sci. Rep</strong>. 2017, 7 (1), 11870.</p> <p> </p> <p>Acknowledgements</p> <p>Financial support is acknowledged from European Union’s 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 813439.</p>

Comparative Electroanalytical Studies of Graphite Flake and Multilayer Graphene Paste Electrodes

In this paper, the fabrication, surface characterisation and electrochemical properties of graphite flake (GFPE) and multilayer graphene (MLGPE) paste electrodes are described. The Raman investigations and scanning electron microscopy were used to analyze and compare structure of both carbon materials. The electroanalytical performance of both electrodes was examined and compared on the basis of the square-wave and cyclic voltammetric behavior of acetaminophen and model redox systems. Results of those studies revealed that GFPE has a larger electroactive surface area and better conductive properties, whilst MLGPE demonstrate better analytical characteristic in case of acetaminophen (AC) determination. AC determination was developed using square wave voltammetry (SWV) and square wave stripping voltammetry (SWSV). For both working electrodes, the process of accumulation enabled us to obtain an extended linear range and to lower the detection limit. In pharmaceutical formulations, AC was determined with good recovery.