Electrochemical determination of zinc(II) using N1-hydroxy-N1,N2-diphenylbenzamidine and multi-walled carbon nanotubes modified carbon paste electrode

In this study, a new carbon paste electrode modified with a laboratory-synthesized ligand, N¹-hydroxy-N¹,N²-diphenylbenzamidine (HDPBA) and multi-walled carbon nanotubes (MWCNTs) (HDPBA‒MWCNTs/CPE) has been developed. The modified electrode was applied for preconcentration and voltammetric determination of zinc ions (Zn(II)) by square wave anodic stripping voltammetry (SWASV). The preconcentration of Zn(II) on the electrode surface was performed in 0.1 M Brinton Robinson (B-R) buffer solution (pH 6) at an applied potential of -1.30 V versus Ag/AgCl for 120 s, followed by stripping in the positive potential scan of the SWASV after a quit time of 10 s. Under optimized experimental conditions, the proposed electrode exhibited a wider linear dynamic response for Zn(II) in a concentration range of 0.02-10.00 μM with a detection limit of 2.48 nM. This is due to the excellent metal-chelation property of the ligand, and the good conductivity and large surface area of MWCNTs which significantly improved the sensing performance of the nanocomposite modified electrode. The selectivity of the electrode was studied by evaluating the interference effects of various foreign ions on the peak current of Zn(II). The method exhibited high reproducibility with a relative standard deviation (RSD) of 3.1%. The present method was applied for the determination of zinc ions in water samples. The recovery values in the tested samples were found to be 98.50-106.0%, indicating a good accuracy of the proposed electrode. Furthermore, the electrochemical behavior of HDPBA in acetonitrile and aqueous solutions has been studied.

Highly sensitive square wave voltammetric method for determination of brucine in artificial urine samples based on choline chloride modified glassy carbon electrode

This paper demonstrates a highly sensitive Voltammetric sensor for determination of brucine (BRU) in artificial urine sample based on choline chloride modified glassy carbon electrode (ChCl/GCE). The simple and cost effective modification was performed by electrodeposition of choline chloride on glassy carbon electrode surface using cyclic voltammetry technique. The modified electrode surface was characterized by electrochemical, spectroscopic and microscopic imaging. The electrode yields a well-resolved peak current for the irreversible oxidation of brucine in the first scan and a pair of quasi-reversible peaks during the second scan. The CV study indicates that brucine undergoes an adsorption controlled electrochemical process with equal number of electrons and protons transfer on the ChCl/GCE. The SWV result shows that the reduction peak current of BRU at the ChCl/GCE was linear in the range of 0.001 μM-10 μM with limit of detection 8 × 10^-5 μM, limit of quantification 2.6 × 10^-4 μM and sensitivity of 116.4 μA/μM. The ChCl/GCE also showed an excellent selectivity, reproducibility and long-time stability towards the electrochemical reduction of Brucine. Moreover, the practical applicability of the fabricated ChCl/GCE was examined in order to determine BRU in artificial urine samples with recovery ranging from 95.5 to 102.7%. The validity of the developed method was confirmed by chromatographic techniques, high-performance liquid chromatography (HPLC) and the results obtained are consistent the HPLC method.

Electrochemical determination of vitamin B6 in pharmaceutical and energy drink samples

A simple and low-cost electrochemical sensor based on poly(phenylalanine) and function­nalized multi-walled carbon nanotubes (F-MWCNTs) modified glassy carbon electrode (GCE) was developed for the determination of vitamin B6 (VB6). The surface morphology of modified glassy carbon electrodes was investigated with scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The electrocatalytic activities of the bare and modified electrodes were investigated in the presence of ferri-ferrocyanide redox couple using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The exchange current density (jo = 2462 µA cm-2) and electron transfer rate constant (ko = 0.002 cm s−1) were calculated using 5 mM K3[Fe(CN)6]. The electro­chemical activity of poly(phenylalanine)/F-MWCNT/GCE towards VB6 oxidation was investigated using CV. Parameters including the number of electrons transferred (n = 2), number of protons transferred (H+ = 2), electron transfer coefficient (α = 0.51) and surface concentration of VB6 (G = 0.24 nmol cm−2) were calculated. At the optimal experimental conditions, the oxidation peak current of VB6 measured by square wave voltammetry (SWV) was found proportional to its concentration in two linear ranges of 0.5 to 20 µM and 20 to 200 µM with a low detection limit (LOD) of 0.038 µM and limit of quantification (LOQ) of 0.125 µM. Finally, the sensor was successfully used to determine VB6 in soft drink and pharmaceutical formulation samples.

Development of a new electrochemical method for the determination of copper(ii) at trace levels in environmental and food samples

This paper presents the fabrication of a new modified carbon paste electrode (CPE) with N 1-hydroxy-N 1,N 2-diphenylbenzamidine (HDPBA) and functionalized multi-walled carbon nanotubes (MWCNTs) (HDPBA-MWCNTs/CPE) for highly sensitive and selective determination of Cu(ii) using the square wave anodic stripping voltammetry (SWASV) technique. The fabricated electrode was characterized using various spectroscopic techniques to study its morphological, structural, and electrochemical properties. The accumulation of Cu(ii) on the surface of HDPBA-MWCNTs/CPE was done in 0.1 M ammonium chloride (NH4Cl, pH 5) solution at an applied potential of -0.70 V versus Ag/AgCl for 180 s, followed by electrochemical stripping in the positive scan of the voltammetry after a resting time of 10 s. The developed HDPBA-MWCNTs/CPE was found to be highly selective, sensitive and reproducible. At optimal conditions of the experiment, the proposed method exhibited a very low limit of detection (0.0048 nM Cu(ii)), a wide linear dynamic range (0.00007-1.5000 μM Cu(ii)), and good reproducibility with relative standard deviation (RSD) value of 3.7%. The effect of various foreign ions on the voltammetric response of Cu(ii) was investigated and the electrode was found to be highly selective to Cu(ii). The practical applicability of the proposed HDPBA-MWCNTs/CPE was studied by applying the electrode for the quantification of Cu(ii) contents in environmental water (wastewater and tap water), soft drink (Fanta and Sprite), and food supplement (commercially available multi-mineral/vitamin tablets) samples. The present method was validated with atomic absorption spectrometry (AAS). The results found from the two methods are in good agreement with a 95% confidence level.

Sensitive and selective determination of vitamin B2 in non-alcoholic beverage and milk samples at poly (glutamic acid)/zinc oxide nanoparticles modified carbon paste electrode

Background

The deficiency of vitamin B2 can lead to many health problems. Therefore, it is necessary to develop a sensitive, selective and fast method for the determination of vitamin B2 in food samples. In this work, a sensitive, selective and low-cost electrochemical sensor was developed using poly (glutamic acid) and Zinc oxide nanoparticles (ZnO NPs) for vitamin B2 in non-alcoholic beverage and milk samples.

Methods

The modification of the electrode surface was carried out by electropolymerization of glutamic acid on ZnO NPs–carbon paste electrode (ZnO NPS–CPE). The prepared electrodes were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and X-Ray diffraction (XRD). CV and square wave voltammetry (SWV) were used to investigate the electrochemical behavior of vitamin B2 at the modified electrode. The effect of various parameters such as amount of ZnO NPs, polymerization cycle, concentration of the monomer, pH, scan rate and accumulation time were optimized to obtain maximum sensitivity at the modified electrode.

Results

The developed sensor showed high electrocatalytic activity towards vitamin B2. Under the optimized conditions, the developed sensor showed a linear response in the range 0.005–10 µM with a low detection limit of (LOD) 0.0007 ± 0.00001 µM and high sensitivity of 21.53 µA/µM.

Conclusions

A reproducible, repeatable, stable and selective sensor was successfully applied for the quantification of vitamin B2 in beverage and milk samples with acceptable recoveries in the range of 88–101%.

A Novel Carbon Paste Electrode Modified with N1-Hydroxy-N1,N2-Diphenylbenzamidine for the Electrochemical Determination of Cadmium(II) in Environmental Samples

The present study introduces a novel electrode for rapid, highly sensitive, and selective electrochemical sensor for cadmium(II) using 5% N¹-hydroxy-N¹,N²-diphenylbenzamidine (HDPBA) modified carbon paste electrode (CPE) (HDPBA‒CPE). Surface characterizations and structural analysis of the proposed HDPBA‒CPE were performed using several analytical techniques. The voltammetric measurements of Cd(II) were conducted by cyclic voltammetry (CV) and square wave anodic stripping voltammetry (SWASV). Several experimental conditions such as composition and pH of buffer solutions, HDPBA composition, accumulation potential and time, and other voltammetric conditions were optimized. Cd(II) was preconcentrated on the modified electrode surface for 270 s using Britton Robinson (B-R) buffer (0.1 M, pH 4) at -1.0 V versus Ag/AgCl, followed by electrochemical oxidation of the accumulated Cd(II) in the positive scan of SWASV after a quiet time of 10 s. Under optimized parameters, the proposed method showed a linear range of 0.3-100 nM Cd(II) with a detection limit of 0.032 nM. The fabricated HDPBA-modified carbon paste electrode exhibited excellent sensitivity, selectivity, stability, and reproducibility (with RSD of 3.8%). The developed HDPBA‒CPE was used for the quantification of Cd(II) in tobacco and environmental water samples, and it was found to be applicable for the determination of different types of real samples.