Anti‐cancer Herbal Drug Berberine – Sensitive Determination Using Boron‐doped Diamond Electrode

Determination of berberine, an isoquinoline plant alkaloid, with antibacterial, antiparasitic, antifungal, hypotensive and antitumoral effects, was proposed by introducing square wave voltammetry on boron‐doped diamond electrode. At optimized experimental parameters, in Britton‐Robinson buffer solution pH 5 berberine provides 3 oxidation peaks (+0.63; +1.14 and +1.34 V) and one reduction (+0.15 V) (vs. Ag/AgCl electrode), with good repeatability (relative standard deviation of 2.6 % and 1.9 % for 8 measurements at 0.5 and 10 µM concentration level, respectively). Calibration curve was linear in wade linear range from 0.1 to 50 µM with limit of detection of 0.04 µM. The proposed procedure was successfully applied for the determination of berberine in seed extract from Argemone mexicana with satisfactory recovery (102–102.6 %). The developed method may represent a sensitive alternative to highly toxic mercury electrodes, modified electrodes and chromatographic methods.     

Voltammetric Behavior of Nitrofurazone at Highly Boron Doped Diamond Electrode

The electrochemical behavior of nitrofurazone (NFZ) at a highly boron doped diamond (BDD) electrode was studied in Britton‐Robinson (BR) buffer using cyclic voltammetry. NFZ was directly reduced to the amine derivative (RNH₂) in the pH range of 2.0 to 4.0 in a process involving six (6.0±0.4) electrons and six protons. In the range of pH 7.0 to 12 and, predominantly aqueous medium, the reduction step split into its two components: the reduction of NFZ to the radical anion (RNO₂^.?) and reduction of RNO₂^.? to hydroxylamine derivative (RNHOH) in processes involving one and three (3.1±0.1) electrons, respectively. On the anodic scan of the voltammograms and at pH 8.0, the oxidation of the hydroxylamine to the nitroso derivative (RNO), was observed in a process involving 2 (1.7±0.2) electrons and 2 protons. In addition and unreported in the literature on any electrode material, was the detection of a new oxidation peak at pH>8.0, which was observed regardless of whether NFZ had been previously reduced or not. The calculation of n, number of electrons, involved in each electrochemical step was satisfactorily accomplished using the Randles‐?evcik equation.     

Square‐Wave Voltammetry Determination of Aspartame in Dietary Products Using a Boron‐Doped Diamond Electrode

Abstract

The use of square‐wave voltammetry in conjunction with a cathodically pretreated boron‐doped diamond electrode for the analytical determination of aspartame in dietary products is described. In this determination, the samples were analyzed without previous treatment in a 0.5 mol l^?1 H₂SO₄ solution. A single oxidation peak at a potential of 1.6 V vs. Ag/AgCl (3.0 mol l^?1 KCl) with the characteristics of an irreversible reaction was obtained. The analytical curve was linear in the aspartame concentration range 9.9×10^?6 to 5.2×10^?5 mol l^?1 with a detection limit of 2.3×10^?7 mol l^?1. The relative standard deviation (n=5) obtained was smaller than 0.2% for the 1.0×10^?4 mol l^?1 aspartame solution. The proposed method was applied with success to the determination of aspartame in several dietary products and the results were similar to those obtained using an HPLC method at 95% confidence level.     

Sensitive Determination of the Diquat Herbicide in Fresh Food Samples on a Highly Boron‐Doped Diamond Electrode

The highly boron‐doped diamond electrode (HBDD) combined with square wave voltammetry (SWV) was used in the development of an analytical procedure for diquat determination in potato and sugar cane samples and lemon, orange, tangerine and pineapple juices. Preliminary experiments realised in a medium of 0.05 mol L^?1 Na₂B₄O₇ showed the presence of two voltammetric peaks around ?0.6 V and around ?1.0 V vs. Ag/AgCl/Cl^? 3.0 mol L^?1, where the first peak could be successfully used for analytical proposes due the facility in the electrode surface renovation. After the experimental and voltammetric optimisation, the calculated detection and quantification limits were 1.6×10^?10 mol L^?1 and 5.3×10^?10 mol L^?1 (0.057 µg L^?1 and 0.192 µg L^?1, respectively), which are lower than the maximum residue limit established for fresh food samples by the Brazilian Sanitary Vigilance Agency. The proposed methodology was used to determine diquat residues in potato and sugar cane samples and lemon, orange, tangerine and pineapple juices and the calculated recovery efficiencies indicated that the proposed procedure presents higher robustness, stability and sensitivity, good reproducibility, and is very adequate for diquat determination in complex samples.     

Polymer‐coated Boron Doped Diamond Optically Transparent Electrodes for Spectroelectrochemical Sensors

Spectroelectrochemical sensors combine electrochemistry, spectroscopy, and partitioning into a film to provide improved selectivity for the target analyte. The sensor usually consists of an optically transparent electrode (OTE) coated with a charge selective polymer film. The polymer film is chosen to pre‐concentrate analyte at the OTE surface to improve the sensitivity and provide selectivity against like charged interferences. OTEs such as Indium Tin Oxide (ITO) have been used extensively for spectroelectrochemical sensors, but little is known about the applicability of such sensors using other OTE materials, such as Boron Doped Diamond (BDD). One distinct advantage of BDD OTEs over ITO OTEs is their significant increase in sensitivity for organic compounds, such as 4‐aminophenol and hydroquinone. We have developed absorption and fluorescence‐based sensing methods with a BDD OTE coated with a sulfonated ionomer film, Nafion. This is demonstrated with tris(2,2′‐bipyridyl)ruthenium(II) ion [Ru(bpy)₃²⁺] using an attenuated total reflectance (ATR) flow cell setup for both absorption and fluorescence. With a Nafion coated BDD optically transparent thin layer electrode (OTTLE), we developed a fluorescence based sensor for a common polyaromatic hydrocarbon (PAH), 1‐hydroxypyrene (1‐pyOH), achieving a detection limit of 80 nM (17 ppb). This work manifests new sensing applications while broadening the use of spectroelectrochemistry, OTEs, and BDD as an electrode material.     

Electroanalytical Determination of Promethazine Hydrochloride in Pharmaceutical Formulations on Highly Boron‐Doped Diamond Electrodes Using Square‐Wave Adsorptive Voltammetry

The electrochemical oxidation of promethazine hydrochloride was made on highly boron‐doped diamond electrodes. Cyclic voltammetry experiments showed that the oxidation mechanisms involved the formation of an adsorbed product that is more readily oxidized, producing a new peak with lower potential values whose intensity can be increased by applying the accumulation potential for given times. The parameters were optimized and the highest current intensities were obtained by applying +0.78 V for 30 seconds. The square‐wave adsorptive voltammetry results obtained in BR buffer showed two well‐defined peaks, dependent on the pH and on the voltammetric parameters. The best responses were obtained at pH 4.0, frequency of 50 s^?1, step of 2 mV, and amplitude of 50 mV. Under these conditions, linear responses were obtained for concentrations from 5.96×10^?7 to 4.76×10^?6 mol L^?1, and calculated detection limits of 2.66×10^?8 mol L^?1 (8.51 μg L^?1) for peak 1 and of 4.61×10^?8 mol L^?1 (14.77 μg L^?1) for peak 2. The precision and accuracy were evaluated by repeatability and reproducibility experiments, which yielded values of less than 5.00% for both voltammetric peaks. The applicability of this procedure was tested on commercial formulations of promethazine hydrochloride by observing the stability, specificity, recovery and precision of the procedure in complex samples. All results obtained were compared to recommended procedure by British Pharmacopeia. The voltammetric results indicate that the proposed procedure is stable and sensitive, with good reproducibility even when the accumulation steps involve short times. It is therefore very suitable for the development of the electroanalytical procedure, providing adequate sensitivity and a reliable method.     

纳米结构的钯与金-钯薄膜的制备及其电催化活性

应用电位扫描法将Pd(II)离子沉积到玻碳电极表面,形成纳米结构的金属钯薄膜电极.然后在酸性溶液中控制适当的阴极电位,使该薄膜电极的钯吸收足量的活性氢,进而以吸收的氢作还原剂将Au(III)离子还原,制得Au-Pd双金属薄膜电极.扫描电镜、循环伏安法等测试表明,该电极Au-Pd沉积层对乙醇的氧化具有很高的电催化活性.     

Application of a Deconvolutive Procedure to Analyze Several Chlorophenol Species in Natural Waters by Square‐Wave Voltammetry on the Boron‐Doped Diamond Electrode

Abstract

The anodic voltammetric behavior of 4‐chlorophenol (4‐CP) on a boron‐doped diamond electrode (BDD) in aqueous solution was studied by square‐wave voltammetry. After optimization of the experimental conditions, 4‐CP was determined in a Britton‐Robinson buffer solution with pH 6.0, prepared with pure water. Moreover, mixtures of some different chlorophenols were also investigated and an analytical method was developed for the simultaneous determination of these compounds in natural waters. The oxidation of 4‐CP on BDD was used for analytical purposes and quantification limits as low as 9.2 µg L^?1 were obtained. This result illustrates the advantage of using oxidation process currents on BDD electrodes as the analytical signal, even in contaminated matrices. In order to compare the results found here with the conventional methodology to determine chlorophenols, HPLC‐UV‐vis measurements were also performed and were in good agreement with the analytical values obtained by SWV.     

Electrochemical behaviors of native and thermally denatured fish DNA in the presence of cytosine derivatives and porphyrin by cyclic voltammetry using boron-doped diamond electrode

The electrochemical behaviors of native and thermally denatured fish DNA was investigated using boron-doped diamond (BDD) film electrode by cyclic voltammetry. The BDD electrode afforded us to measure weak current less than muA for the DNA solution in 100 microl. The mixture of acetic acid and sodium acetate solution (0.2 M) was used as a supporting electrolyte. Two oxidation peaks were observed at about +1.1 V and +1.3 V at pH 4.6 for thermally denatured fish DNA. This is due to the oxidation of guanine and adenine in the denatured fish DNA, respectively. In contrast, the native fish DNA showed ill-defined peaks at +1.1 V. Furthermore, the electrochemical behaviors of thermally denatured fish DNA were studied in the presence of cytosine, cytidine, cytidine-5-monophosphate, tetrakis(1-methypyridinium-4-yl)porphyrin (H(2)(TMPyP)(4+)) and Ru(II)(TMPyP)(4+). The oxidation peak intensity at +1.1 V gradually decreased with the increase of the concentrations of the above compounds. Based on the above studies, electrochemical behaviors of the thermally denatured fish DNA at BDD electrode is discussed.     

Speciation of arsenic(III) and arsenic(V) by manganese-mediated stripping voltammetry at gold microelectrode ensemble in neutral and basic medium

New schemes of arsenic speciation by anodic stripping voltammetry are developed at neutral pH based on the difference in electrochemical behaviour of the As(III) and As(V) forms. Detection is performed in sulphite medium (0.1 M Na₂SO₃) in the presence of Mn(II) (10^?6 M), which is known to catalyse the reduction of As(V), making it detectable by ASV. Two speciation schemes are proposed. If As(III) > As(V), then As(III) and total As(III) + As(V) are determined in separate voltammetric cells after oxidation of As(III) to As(V) (5 min ozone purging), similar to previous studies. However, when As(V) > As(III), both As(III) and As(V) can be determined consecutively, within the same cell. In this case, two simple variants were successfully tested, depending on the size of the As(III) peak in comparison to the linearity range. The working electrode is an ensemble of gold microelectrodes obtained by HAuCl₄ electrolysis at a carbon black–polyethylene composite (ratio 30:70). No purging is required, the electrode is sensitive, robust and has a long lifetime. Calculated LODs of As(III) and As(V) are 0.09 μg L^?1 and 0.35 μg L^?1, respectively (3σ, t_dep = 20 s). The proposed procedures are fast, simple and environmental-friendly.     

Anodic Oxidation Behaviors of Formaldehyde at Boron‐Doped Diamond Electrodes

The electrochemical behaviors of formaldehyde (FA) at boron‐doped diamond (BDD) electrodes are investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear scanning voltammetry (LSV) techniques. The CV results show that the oxidation reaction of FA is influenced by the hydroxyl concentration in the solution, and the peak current response with the FA concentration is linear at the range from 10 to 100 mM. The differential capacitance from EIS results indicate that the FA molecules adsorb at the BDD electrode surface at low potential (from 1.0 to 1.4 V). The kinetic studies have been examined with the various concentrations of FA, pH, and temperature. The activation energy of FA oxidation is also calculated. The results of kinetic study indicate that the adsorption of FA molecules at the BDD electrode is the rate‐determining step at low potential (from 1.0 to 1.40 V).     

An Experimental Design for Simultaneous Determination of Carbendazim and Fenamiphos by Electrochemical Method

This study is aimed to develop an electroanalytical methodology using a boron‐doped diamond electrode (BDD) associated with experimental design in order to determine simultaneously and selectively carbendazin (CBZ) and fenamiphos (FNP) pesticides. In previous studies oxidation peaks were observed at 1.10 V (CBZ) and 1.20 V (FNP), respectively, with characteristics of irreversible processes controlled by diffusion of species (in pH 2.0 (CBZ) and pH 3.5 (FNP)) using a BR buffer 0.1 mol L^?1 as support electrolyte. The differences between the potentials for both pesticides, (about 100 mV) indicate the possibility of selective determination of FNP and CBZ. However, employing an equimolar mixture of analytes, the peaks overlap to form a single oxidation peak. Thus, we used a 3⁴ full factorial design with four parameters to be analyzed in three levels, in order to obtain the optimized parameters for the separation of the peaks. The best separation conditions were pH 5.0, square wave frequency of 300 s^?1, pulse amplitude of 10 mV and scan increment of 2 mV. These parameters were used to obtain the calibration curves of CBZ and FNP. For CBZ the analytical curve was obtained in the concentration range of 4.95×10^?6 to 6.90×10^?5 mol L^?1 with good sensitivity and linearity (0.175 A/mol L^?1 and 0.999, respectively). The limits of detection (LOD) and quantification (LOQ) were 1.6×10^?6 mol L^?1 and 5.5×10^?6 mol L^?1, respectively. For FNP the linear concentration interval was 4.95×10^?6 to 3.67×10^?5 mol L^?1, with a sensitivity of 0,207 A/mol L^?1 and linearity of 0.996. The LOD and LOQ were 4.1×10^?6 mol L^?1 and 13.7×10^?6 mol L^?1, respectively. Using these experimental conditions it was possible to separate the oxidation peaks of CBZ (E_p=1.08 V) and FNP (E_p=1.23 V). The electroanlytical method was applied in lemon juice samples. The recovery values were 110.0 % and 92.5 % for CBZ and FNP, respectively. The results showed that the developed method is suitable for application in foodstuff samples.     

Electron Transfer Kinetics of Ferrocene at Microcrystalline Boron‐Doped Diamond Electrodes: Effect of Solvent and Electrolyte

Cyclic voltammetric measurements were made using well‐characterized microcrystalline boron‐doped diamond thin‐film electrodes to test the material's responsiveness for ferrocene as a function of scan rate, solvent, and electrolyte composition. Apparent heterogeneous electron transfer rate constants, k°_app, of 0.042±0.015, 0.048±0.015, and 0.008±0.002 cm/s were observed in 0.1 M NaClO₄/CH₃CN, 0.1 M TBAClO₄/CH₃CN, and 0.1M TBAClO₄/CH₂Cl₂, respectively. These rate constants, obtained using electrodes without any type of pretreatment, are similar to those observed for freshly polished glassy carbon. The results demonstrate that boron‐doped diamond is a viable material for the electrochemical analysis of nonaqueous analytes.     

Oxidation of Electrodeposited Copper on Boron Doped Diamond in Acidic Solution: Manipulating the Size of Copper Nanoparticles Using Voltammetry

The in situ deposition of copper, in acidic solution onto a Boron Doped Diamond electrode, using cyclic voltammetry is explored and produced surfaces are imaged using Atomic Force Microscopy. A uniformly dense covering of copper nanoparticles is produced when the potential of a freshly polished BDD electrode is swept from 0 V in a negative direction. For example, in 1 M H₂SO₄ with a Cu(II) concentration of 1 mM, nanoparticles of height 10.1 nm, diameter 74.6 nm and a density of 16.1 particles per μm² are created when the potential is swept to ?0.35 V. The higher the concentration of Cu(II) in solution or the larger the magnitude of the end potential the larger the nanoparticles are and the more densely they are spread. When the direction of the scan is reversed and a positive potential sweep carried out evidence from the observed cyclic voltammograms and AFM images shows that copper is being incompletely stripped from the electrode surface. If the potential is then cycled continuously ten times, as would happen when the process is used for electroanalytical purposes, then an irregular and irreproducible deposit is observed. One can infer from this evidence that the incompletely stripped copper is electrochemically active and therefore adversely affecting subsequent deposition processes. Comparison to existing literature shows that the discrete application of particular deposition and stripping potentials is a much better way to produce a deposit of copper nanoparticles than application of potential through cyclic voltammetry.     

Wide linear range nanomaterial/ionophore-based electrode used for determination of lead in environmental and biological samples with differential pulse voltammetry

A new chemically modified carbon paste electrode is fabricated to determine lead ion concentration in its trace level in aqueous media with differential pulse voltammetry (DPV). The best performance is obtained by the carbon paste electrode composition including 20% of dithiodibezoic acid (DDA), 80% of high purity graphite powder and 60?µL of colloidal gold nanoparticle (AuNP) solution. The proposed electrode has a wide linear calibration response from 1?×?10^?9 to 6?×?10^?5 M with a detection limit of 6.6?×?10^?10?M, at pH 3.5. Seven replicate determination of 5?×?10^?8?M of lead ion concentration gives a relative standard deviation of 3.33%. The modified sensor is applied to determine lead contents in some environmental and biological Samples with satisfactory results.