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.     

Electroactive LbL films of metallic phthalocyanines and poly(<Emphasis Type="Italic">0</Emphasis>-methoxyaniline) for sensing

Multilayered nanostructured films have been widely investigated for electrochemical applications as modified electrodes, including the layer-by-layer (LbL) films where properties such as thickness and film architecture can be controlled at the molecular level. In this study, we investigate the electrochemical features of LbL films of poly(o-methoxyaniline; POMA) and tetrasulfonated phthalocyanines containing nickel (NiTsPc) or copper (CuTsPc). The films displayed well-defined electroactivity, with redox pairs at 156 and 347 mV vs SCE, characteristic of POMA, which allowed their use as modified electrodes for detecting dopamine and ascorbic acid at concentrations as low as 10⁻⁵ M. This paper is dedicated to Prof. Francisco Nart, in memoriam.     

Development of an Electroanalytical Method for the Quantification of Zearalenone (ZEA) in Maize Samples

The application of electroanalytical techniques to detect and quantify zearalenone (ZEA) mycotoxin that frequently contaminates maize and foodstuff is studied in this work. Rice and maize grains were inoculated with Fusarium fungus to obtain ZEA in artificially infected samples. The electro‐oxidation of ZEA adsorbed on the surface of glassy carbon (GC) electrodes in 20% acetonitrile (ACN)+80% 1 M HClO₄ (aqueous solution) reaction medium was studied by using square‐wave voltammetry (SWV). Studies were conducted to find the most favorable accumulation potential (E_acc) and accumulation time (t_acc) to perform the ZEA preconcentration on the electrode surface. It was found that E_acc was any value in the range from 0.00–0.90 V and the best t_acc was 120 s, respectively, for ZEA separated from extracting solution by TLC (ZEA_TLC) while E_acc=0.90 V corresponded to ZEA in non separated matrix solution (ZEA_matrix). The ZEA quantitative determination was performed by SWV combined with the standard addition method. Linear plots were obtained from the net peak current (I_{p, n}) vs c*_ZEA in the concentration range from 20 to 3184 ppb. Detection limit of 30 ppb at a signal to noise ratio of 3 : 1 was obtained. On the other hand, recovery experiments were performed on uncontaminated maize samples spiked with ZEA.     

Characterization and Use of Copper Solid Amalgam Electrode for Electroanalytical Determination of Triazines‐Based Herbicides

This paper reports the construction, characterization and use of copper solid amalgam electrode in the study of the electrochemical behavior of atrazine and ametryne herbicides by square‐wave voltammetry. This study was used as basis for the development of sensitive analytical methods for the determination of these herbicides in natural water, avoiding the use of mercury, by means of a solid electrode that presents high sensitivity and minimizes any environment contamination with mercury residues. The experimental and voltammetric conditions were evaluated and the results showed a reduction peak for atrazine at ?0.98 and at ?1.1 V vs. Ag/AgCl 3.0 mol L^?1 for ametryne, both with characteristic of an irreversible electrode reaction in an electrochemical diffusion controlled process, involving two electrons for each herbicide reduction. Based on voltammetric studies, it has been demonstrated that the most possible mechanism for the reduction of herbicides involved reduction of bond carbon‐chloride for atrazine and the reduction of bond carbon–SCH₃ for ametryne. The detection limit of herbicides obtained in pure water (laboratory samples) was shown to be lower than the maximum limit of residue established for natural water by the Brazilian Environmental Agency, demonstrating that this methodology is very suitable for determining any contamination by atrazine and ametryne residues in different samples, proving a good substitute for mercury electrodes.     

Electroanalytical Determination of N‐Nitrosamines in Aqueous Solution Using a Boron‐Doped Diamond Electrode

The electrochemical methods cyclic and square‐wave voltammetry were applied to develop an electroanalytical procedure for the determination of N‐nitrosamines (N‐nitrosopyrrolidine, N‐nitrosopiperidine and N‐nitrosodiethylamine) in aqueous solutions. Cyclic voltammetry was used to evaluate the electrochemical behaviors of N‐nitrosamines on boron‐doped diamond electrodes. It was observed an irreversible electrooxidation peak located in approximately 1.8 V (vs. Ag/AgCl) for both N‐nitrosamines. The optimal electrochemical response was obtained using the following square‐wave voltammetry parameters: f=250 Hz, E_sw=50 mV and E_s=2 mV using a Britton–Robinson buffer solution as electrolyte (pH 2). The detection and quantification limits determined for total N‐nitrosamines were 6.0×10^?8 and 2.0×10^?7 mol L^?1, respectively.     

Electrochemical and Spectroelectrochemical Analysis of 4‐(4‐(5‐Phenyl‐1,3,4‐oxadiazole‐2‐yl)phenoxy)‐Substituted Cobalt(II), Lead(II) and Metal‐Free Phthalocyanines

Electrochemical and spectroelectrochemical analyses of 4‐(4‐(5‐phenyl‐1,3,4‐oxadiazole‐2‐yl)phenoxy)‐substituted metal‐free phthalocyanine ( H₂Pc ( 1 )) and metallated phthalocyanines ( PbPc ( 2 ) and CoPc ( 3 )) were performed in solution. Voltammetric characterizations of the phthalocyanine complexes were investigated by using cyclic voltammetry and square wave voltammetry techniques. CoPc ( 3 ) gave common metal and ring based electron transfer reactions; however they split due to the aggregation. Although PbPc ( 2 ) illustrated reversible reduction processes during the voltammetric measurements, it was de‐metallized and thus turned to the metal free phthalocyanine during repetitive voltammetric cycles and in situ spectroelectrochemical measurements.     

Electroanalytical Determination of Cd(II) and Pb(II) in Bivalve Mollusks using Electrochemically Reduced Graphene Oxide‐based Electrode

An electrochemical sensor for the simultaneous determination of Cd(II) and Pb(II) by square wave anodic stripping voltammetry (SWASV) in bivalve mollusks using a glassy carbon electrode modified with electrochemically reduced graphene oxide has been developed. The modified surface was characterized by cyclic voltammetry, high resolution scanning electron microscopy (HR‐SEM), and Raman spectroscopy. The optimum conditions were optimized and a linear range was observed from 15–105 μg L^?1 with a limits of detection of 15 μg L^?1 for Cd(II) and Pb(II). The methodology was validated and applied in different samples of commercial bivalve mollusks with satisfactory results. The high conductivity and greater surface area of the modifying agent improves the preconcentration capacity of the electrochemical sensor, allowing to develop a simple, rapid and sensitive analysis in the detection of lead and cadmium in marine resources.     

Trace Determination of Chromium by Square‐Wave Adsorptive Stripping Voltammetry on Bismuth Film Electrodes

This works reports the use of adsorptive stripping voltammetry (AdSV) for the trace determination of chromium on a rotating‐disk bismuth‐film electrode (BFE). During the reductive accumulation step, all the chromium species in the sample were reduced to Cr(III) which was complexed with cupferron and the complex was accumulated by adsorption on the surface of a preplated BFE. The stripping step was carried out by using a square‐wave (SW) potential‐time voltammetric signal. Electrochemical cleaning of the bismuth film was employed, enabling the same bismuth film to be used for a series of measurements in the presence of dissolved oxygen. The experimental variables as well as potential interferences were investigated and the figures of merit of the method were established. Using the selected conditions, the 3σ limit of detection for chromium was 100 ng L^?1 (for 120 s of preconcentration) and the relative standard deviation was 3.6% at the 2 μg L^?1 level (n=8). Finally, the method was applied to the determination of chromium in real samples with satisfactory results.     

DPV and SWV Determination of Estrone Using a Cathodically Pretreated Boron‐Doped Diamond Electrode

Voltammetric methods for estrone determination were developed using a cathodically pretreated BDD electrode with DPV or SWV. Analytical curves were obtained for estrone concentrations from 0.20 or 0.10 to 2.0 µmol L^?1, for DPV or SWV, with detection limits of 0.20 and 0.10 µmol L^?1, respectively. The SWV method was successfully applied in estrone recovery studies in different water matrices. Additionally, these recovery results were reasonably similar to those attained using HPLC/UV‐vis. Comparatively to other electroanalytical methods based on different carbon electrodes, the here‐reported novel methods yield very good results, being adequate for estrone determination in environmental samples.     

A New Indirect Electroanalytical Method to Monitor the Contamination of Natural Waters with 4‐Nitrophenol Using Multiwall Carbon Nanotubes

The electrochemical detection of the hazardous pollutant 4‐nitrophenol (4‐NP) at low potentials, in order to avoid matrix interferences, is an important research challenge. This study describes the development, electrochemical characterization and utilization of a multiwall carbon nanotube (MWCNT) film electrode for the quantitative determination of 4‐NP in natural water. Electrochemical impedance spectroscopy measurements showed that the modified surface exhibits a decrease of ca. 13 times in the charge transfer resistance when compared with a bare glassy carbon (GC) surface. Voltammetric experiments showed the possibility to oxidize a hydroxylamine layer (produced by the electrochemical reduction of 4‐NP on the GC/MWNCT surface) in a potential region which is approximately 700 mV less positive than that needed to oxidize 4‐NP, thus minimizing the interference of matrix components. The limit of detection for 4‐NP obtained using square‐wave voltammetry (0.12 μmol L^?1) was lower than the value advised by EPA. A natural water sample from a dam located in São Carlos (Brazil) was spiked with 4‐NP and analyzed by the standard addition method using the GC/MWCNT electrode, without any further purification step. The recovery procedure yielded a value of 96.5% for such sample, thus confirming the suitability of the developed method to determine 4‐NP in natural water samples. The electrochemical determination was compared with that obtained by HPLC with UV‐vis detection.     

Electrochemical Determination of Cu(II) Ions in Chloride‐Rich Environment Using Polyviologen‐Modified Glassy Carbon Electrodes

Polyviologen was formed on glassy carbon electrodes using potentiostatic electropolymerization in pH 4.2 Britton‐Robinson buffer solution. The polyviologen‐modified glassy carbon electrode (PVGCE) was employed to determine Cu(II) in chloride‐rich solutions in order to demonstrate the electroanalytical application of polyviologen. The PVGCE was found capable of enhancing the detection limit of Cu(II) in chloride‐rich environment because of the anion‐exchange feature of the polymer film. Cathodic stripping square‐wave voltammetry (CSSWV) was employed to determine Cu(II). The dependence of the cathodic stripping current on the concentration of Cu(II) was linear from 0.06 ppm to 9.53 ppm with a regression coefficient of 0.999. The detection limit is 0.02 ppm (σ = 3). Regeneration of the PVGCE can be achieved by simply immersing the electrode in a stirred 0.5 M NaCl solution.     

Microsensor Chip Integrated with Gold Nanoparticles‐Modified Ultramicroelectrode Array for Improved Electroanalytical Measurement of Copper Ions

This paper presents a microsensor chip integrated with a gold nanoparticles‐modified ultramicroelectrode array (UMEA) as the working electrode for the detection of copper ions in water. The microsensor chip was fabricated with Micro‐Electromechanical System technique. Gold nanoparticles were electrodeposited onto the surface of UMEA at a constant potential of ?0.3 V. The ratio d/R_b of interelectrode spacing (d) over the individual electrode’s radius (R_b) was investigated to improve the electrochemical performance. The UMEA with a d/R_b of 20 showed the best hemispherical diffusion mode, resulted in fast response time and high current response. The gold nanoparticles increased the active surface area of UMEA by not changing the geometries of UMEA, and the current response was increased further. Incorporating the optimized characteristic of UMEA and gold nanoparticles, the microsensor showed a good linear range from 0.5 to 200 µg L^?1 of copper ions in the acetate buffer solutions with the method of square wave stripping voltammetry. Compared with the gold nanoparticles‐modified disk electrode, the gold nanoparticles‐modified UMEA showed higher sensitivity (0.024 µA mm^?2 µg^?1 L) and lower limit of detection (0.2 µg L^?1). Water samples from river water and tap water were analyzed by the microsensor chip with recovery ranging from 100.7 % to 107.8 %.     

Development of an Electrochemical Sensor for Selective Determination of Dopamine Based on Molecularly Imprinted Poly(p-aminothiophenol) Polymeric Film

In this study, a molecularly imprinted electrochemical sensor (MIP/DA) was investigated for selective and sensitive determination of dopamine (DA) by electrochemical polymerization of p-aminothiophenol in the presence of DA on gold electrode. According to electrochemical behaviour of the sensor, gained through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), MIP/DA sensor showed distinctive electron transfer characteristics in comparison to the non-imprinted (NIP/DA) sensor. Besides the MIP/DA sensor showed high selectivity for dopamine through its analyte specific cavities. The sensor had a broad working range of 5.0×10⁻⁸–2.0×10⁻⁷ M with a limit of detection (LOD) of 1.8×10⁻⁸ M and the developed sensor was successfully applied for determination of dopamine in pharmaceutical samples.     

Spectroelectrochemical Investigation of TPPMn(III/II)‐Driven Liquid | Liquid | Electrode Triple Phase Boundary Anion Transfer into 4‐(3‐Phenylpropyl)‐Pyridine: ClO4−, CO3H−, Cl−, and F−

The triple phase boundary transfer of anions from the aqueous into an organic phase can be driven electrochemically here with the tetraphenylporphyrinato‐Mn(III/II) (or TPPMn) redox system in 4‐(3‐phenylpropyl)‐pyridine) (or PPP). Anions investigated are perchlorate, chloride, fluoride, and bicarbonate. The bicarbonate and fluoride transfer processes are shown to be chemically more complex compared to the perchlorate and chloride cases with UV‐vis‐spectroelectrochemical measurements indicating a combination of HCO₃^?/CO₃^2? transfer processes and association of fluoride with TPPMn(III)⁺, respectively. In situ spectroelectrochemistry is developed for ion‐transfer voltammetry into sub‐microliter organic phase regions on mesoporous ITO conducting film electrodes.     

Electroanalytical Device for Cadmium Speciation in Waters. Part 1: Development and Characterization of a Reliable Screen‐Printed Sensor

A reliable screen‐printed sensor for cadmium speciation analysis is presented here. Its development has been focused on the achievement of a reproducible and repeatable sensor. The electrode construction and its surface coating are discussed in detail. The optimized procedure has permitted to obtain very accurate sensors with detection limit of 0.2 μg (Cd) L^?1 using SWASV for only 60 s of deposition time. The electrochemically accessible, i.e. potentially bioavailable, fraction of the cadmium present in an untreated river water sample has been successfully quantified without degassing. These results give a glimpse of the potential of this membrane‐free sensor in real matrices.     

Voltammetric Behavior of Mifepristone (RU‐486) Using Square‐Wave and Adsortive Stripping‐Wave Techniques. Determination in Urine Samples

The behavior of Mifepristone (RU‐486) was studied by square‐wave technique, leading to two methods for its determination in aqueous samples and urine samples at pH 2. The application of the square‐wave (SW) without the adsorptive accumulation and stripping voltammetric (AdSV) show the maximum response at ?0.896 V using an accumulation potential of ?0.5 V. The effect of experimental parameters that affect this determination are discussed. For the stripping technique, Mifepristone proved to be more sensitive, yielding signals four times larger than those obtained by applying a square‐wave scan without the previous accumulation. The calibration plot to determine Mifepristone was linear in the range 2.4×10^?8 and 5.4×10^?7 M by stripping mode with an accumulation time t_acc of 30 s. The relative standard deviation obtained for concentration levels of Mifepristone as low as 2.0×10^?7 M with square‐wave was 1.17% (n=10) and with stripping square‐wave 2.02% (n=10) in the same day. The two proposed methods (SW and SWAdSV) were applied to the determination of Mifepristone in urine.     

Simultaneous and Sensitive Detection of Cd(II) and Pb(II) Using a Novel Bismuth Film/Ordered Mesoporous Carbon‐molecular Wire Modified Graphite Carbon Paste Electrode

An electrochemical sensor for the simultaneous and sensitive detection of Cd(II) and Pb(II) is proposed on the basis of square‐wave anodic stripping voltammetry (SWASV) experiments using a novel bismuth film/ordered mesoporous carbon‐molecular wire modified graphite carbon paste electrode (Bi/OMC‐MW/GCPE). Ordered mesoporous carbon (OMC) and molecular wire (MW) (diphenylacetylene) were used as the modifier and binder, respectively. The Bi/OMC‐MW/GCPE was prepared with the addition of graphite powder, OMC and DPA at the ratio of 2 : 1 : 1. The electrochemical properties and morphology of the electrode were characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), SWASV and scanning electron microscopy (SEM). The parameters affecting the stripping current response were investigated and optimized. The experimental results show that the prepared electrode exhibited excellent electrochemical performance, good electrical conductivity and a high stripping voltammetric response. Under optimized conditions, a linear range was achieved over a concentration range from 1.0 to 70.0 μg/L for both Cd(II) and Pb(II) metal ions, with detection limits of 0.07 μg/L for Cd(II) and 0.08 μg/L for Pb(II) (S/N=3) with the deposition time 150 s. Moreover, the sensor exhibited improved sensitivity and reproducibility compared to traditional CPEs. The fabricated electrode was then successfully used to satisfactorily detect Cd(II) and Pb(II) in real soil samples.     

Reaction with N,N‐Diethyl‐p‐phenylenediamine: A Procedure for the Sensitive Square‐Wave Voltammetric Detection of Chlorine

The reaction of chlorine and N,N‐diethyl‐p‐phenylenediamine has been studied as a means of generating an analytical voltammetric signal of much improved sensitivity and selectivity for the detection of the former than is possible via direct electrolysis. A reaction mechanism is suggested whereby the chlorine attacks the primary amine of DEPD to form the N‐chlorinated product that shows a much enhanced signal under conditions of square‐wave voltammetry than does chlorine itself. The analytical parameters were found to vary with concentration of DEPD and a linear range from 17 to 495 μM was achievable with a corresponding limit of detection of 6.8 μM     

Theoretical Treatment of a Cathodic Stripping Mechanism of an Insoluble Salt Coupled with a Chemical Reaction in Conditions of Square Wave Voltammetry. Application to 6‐Mercaptopurine‐9‐D‐Riboside in the Presence of Ni(II)

Cathodic stripping mechanism of an insoluble salt coupled with a homogenous chemical reaction is considered both theoretically and experimentally under conditions of square‐wave voltammetry. For the mercury electrode in aqueous solution, the electrode reaction is described as L(aq)+Hg(l)=HgL(s)+2e^?, where L(aq) is the reactive ligand that forms a sparingly soluble compound HgL(s). The electrode reaction is coupled with a homogenous, first‐order chemical reaction, A(aq)=L(aq). Theoretical predictions are confirmed by experiments with 6‐mercaptopurine‐9‐D‐riboside in the presence of nickel(II) ions.     

Voltammetric Monitoring of Protein Aggregation from Solution Using Tris‐(2,2′‐Bipyridine) Osmium(II) Chloride Complex as an Electrocatalytic Mediator

The present work evaluates the feasibility of tracking protein aggregation voltammetrically by taking advantage of the intrinsic electroactivity of tyrosine residues. The electrocatalytic current due to the oxidation of tyrosine, mediated by tris‐(2,2′‐bipyridine)osmium(II) chloride, is used to report changes in protein aggregation state. We demonstrate, by the use of square wave voltammetry, that this system is able to differentiate between peptides containing equimolar tyrosine concentrations, and even detect tyrosine within large entities such as antibodies and insoluble amyloid fibrils. We also determine the aggregation time course of a model peptide, amyloid beta, detecting species with sizes from monomeric to insoluble aggregate. The method offers the prospect of monitoring biopharmaceutical aggregation and has potential to establish itself as a technique that is orthogonal to existing methods of aggregation detection.