Square-wave Cathodic Stripping Voltammetry Research Articles

An Electrochemical Strategy for Detection of Trace‐Level Binapacryl Using Square‐Wave Cathodic Stripping Voltammetry

AbstractBinapacryl is a fungicide and miticide from the dinitrophenol group and is used to control fungi and mites in agricultural areas. Since even trace amounts of pesticides can be highly toxic to humans and the environment, accurate and sensitive analytical methods are needed for their determination. Therefore, the electrochemical behavior of binapacryl fungicide on the glassy carbon electrode (GCE) was investigated using square wave cathodic stripping voltammetry (SWCSV) and cyclic voltammetry (CV). Some parameters such as accumulation potential, accumulation time, pulse amplitude, frequency, and step potential were optimized on GCE. From the plotted calibration graph, the linear operating range was found to be 0.16–6.20 μM (0.06–2.0 mg/L), and accordingly the limit of detection (LOD) and limit of quantification (LOQ) for the first and second peak were 0.060 μM/0.201 μM and 0.0627 μM/0.209 μM, respectively. The proposed method was applied for spiked tap water, apple juice and grape juice samples. An electroreduction mechanism has also been proposed for binapacryl with the participation of 2e−/2H+ via the nitro group of the molecule. Also, the selectivity of the method was demonstrated by investigating the interference effects of some pesticides on the determination of binapacryl.

Graphene oxide-manganese oxide composite as an electrocatalyst for simultaneous detection of manganese- and chromium-contaminated water.

The development of asensitive and selective electrochemical sensor for simultaneous quantification of manganese (Mn(II)) and chromium (Cr(VI)) using composite of graphene oxide(GO) and manganese oxide modified screen printed carbon electrode (GO-Mn2O3/SPCE) is reported for the first time. The good sensing performance is achieved by mixing GO prepared by modified Hummer's method (GO-H) with proper particle size of Mn2O3 (241 nm). The mechanism of this sensor is based on the formation of Mn-O and Cr-O on the modified electrode with assistance of oxygen moieties provided by both Mn2O3 NPs and GO. The analytical performances were investigated by measuring electrochemical signal of Mn(II) and Cr(VI) by using square-wave cathodic stripping voltammetry (SWCSV). This sensor holds low electrode-to-electrode variation (relative standard deviation (RSD) < 4%) with a good limit of detection (LOD) at about 6.67 and 11.20 μg⋅L-1 for Mn(II) and Cr(VI), respectively. Applicability of this sensor was demonstrated by measuring Mn(II) and Cr(VI) in tap water samples with recovery of 90.77-103.45% and 82.34-103.73% for Mn(II) and Cr(VI) determinations, respectively. With the contribution of both GO and Mn2O3 as electrocatalysts, this developed sensor iscapable to be usedfor water quality monitoring in real samples.

Novel magneto-electrochemical determination of Mn(II)

This study describes the robust modification of a screen-printed carbon electrode (SPE) for the magneto-electrochemical determination of Mn2+, in real soil samples, by square wave cathodic stripping voltammetry (SW-CSV). The carbon surface of a SPE was modified with electrodeposited Au, then dropcast with Fe3O4 NPs functionalised with l-cysteine within a graphene oxide matrix. The magnetic Fe3O4 NPs within the modification significantly increased the diffusion coefficient of the paramagnetic Mn2+ ion during deposition. Likewise, it also increased the number of hydroxyls available for the formation of the MnO2 layer, attributed to chiral induced spin selectivity. The reduced graphene oxide (RGO) served to increase the surface area and heterogenous electron transfer rate of the intermediate reactions. The Au/l-cys/Fe3O4/RGO modification displayed two significant improvements: enhancement of the Mn2+ response signal (212-fold increase) and improved flexibility for the analytical method (linear ranges from 0.5 to 300 µg L-1 to 62 – 1500 µg L-1 using deposition times of 300 or 30 s, respectively). Ten soil sample extracts were tested for Mn2+, by SW-CSV using the Au/l-cys/Fe3O4/RGO modified SPE, and showed good agreement with FAAS, average error of 6.8%.

Near-electrode pH change for voltammetric detection of insoluble lead carbonate

Lead contamination of drinking water is a concern to all inhabitants of old cities where lead pipes and soldering are still present. Simple on-site electrochemical detection methods are promising technologies that have gained attention recently. However, conventional electrochemical techniques only quantify soluble forms of lead in water without accounting for insoluble particulates. Herein, a simple voltammetric technique for quantification of insoluble lead species is reported. Lead carbonate (PbCO3) was used as a model compound to show the possibility of detecting particulate lead species directly in solution without chemical treatment. Specifically, electrochemical generation of protons was used as an alternative method to dissolve PbCO3 and thus obtain a more realistic assessment of lead contamination. Lead was detected using cathodic stripping square wave voltammetry (CSSWV). After applying a high oxidizing potential to the electrode immersed in a PbCO3 solution with solid PbCO3 particulates, a significant increase in current was observed as compared to that of a saturated PbCO3 solution. The signal was proportional to the amount of added PbCO3, even when the solubility limit was exceeded. Thus, the combination of a local pH change with CSSWV provides a simple, rapid, and reagentless method for an in-situ detection of insoluble lead species.

Electrochemical Monitoring of Manganese in Drinking Water

Low levels of Mn are essential for many metabolic processes in the human body, yet excessive exposure to this heavy metal has been correlated to neurodegenerative diseases with Parkinson’s like symptoms in adults and neurological deficits in children. Erosion of Mn rich soil and rocks and human activities directly pollute groundwater which supplies drinking water for 51% of the total US population and 99% of the rural population. Hence contaminated drinking water represents one of the major sources of Mn intake. The non-enforceable updated guideline set by the EPA is 50ppb Mn. Trace metal analytical methods such as ICP-MS and AAS are limited to centralized laboratory testing and not feasible for point-of-care. Our work is aimed at the development of an electrochemical platform for efficient and rapid Mn detection in drinking water. The core technique is Square Wave Cathodic Stripping Voltammetry (SWCSV), carried out on disposable three-electrode sensors with a platinum working electrode, platinum counter electrode and an electroplated Ag/AgCl reference electrode. A 3D printed interface integrates a small vibration motor for effective agitation of the 12µL droplet sample during the deposition phase and allows connection to a commercial potentiostat. Figure 1(a) depicts the hardware components of the platform, with an onset on the sensor configuration. First, the system performances are characterized in standard solutions. Compared to peak amplitude, peak area is found to be a more suitable indicator of Mn concentration, with a linearity of R^2=0.998 in the range 5ppb-200ppb. The introduction of an embedded agitation mechanism allows for a reduction in the limit of quantitation (LOQ) from 5ppb to 3ppb and an approximate 2.3X increase in sensitivity from 9.09nC/ppb to 20.75nC/ppb. Analysis of tap water is then performed to confirm the capabilities of the electrochemical platform in more complex matrices. With optimal SWCSV parameters a limit of quantitation of 6ppb, a sensitivity of 26.45 nC/ppb and a linearity with R^2=0.995 are achieved. The developed protocol requires minimal sample preparation of the water samples, with a 2X dilution in 0.2M Acetate Buffer to provide enough ionic strength to sustain the faradaic reactions and buffer the pH at 4.7. 3-point standard addition is executed to determine the Mn concentration in unknown specimens and performances are compared to ICP-MS on the analysis of 78 tap water and well water samples from Holliston, MA with concentrations in the range 0.03ppb-5.3ppm. 100% agreement, 70% accuracy and 91% precision were obtained. Figure 1(b) shows typical voltammograms from the measurement of the unknown sample and the 3 spikes at known Mn concentrations to implement the 3-point standard addition. To enhance monitoring of water quality in local communities and rural areas, parallelization of the measurements can further reduce the analytical time and improvements in the interface can ultimately make the devised portable and easy-to-use electrochemical station soon deployable for practical on-the-field testing. Figure 1

Determination of Manganese in Human Whole Blood with Indium Tin Oxide Electrochemical Point-of-Care Sensor

Manganese (Mn) is one of the most common elements in the earth’s crust, and its compounds are widely used in consumer products including gasoline, cell phone batteries, fertilizer, pigments, fireworks, etc. Although a trace metal in the human body and under tight homeostatic control, elevated levels of Mn due to occupational or environmental exposure can cause serious adverse health effects, such as manganism (a Parkinsonian-like syndrome), liver cirrhosis, and Behcet disease. The normal range of Mn in blood is 4.7-18.3 µg/L (5-20 ppb), and values greater than 36 µg/L correlate with disease. The current method for analyzing Mn in blood is via inductively coupled plasma mass spectrometry (ICP-MS) in centralized labs, which requires a venipuncture sample, can take 3-6 months for analyses, and can be costly. Electrochemical analysis can offer an attractive alternative, leading to developing a point-of-care system for Mn monitoring in blood, with the advantages of being inexpensive and easily miniaturized. Herein, we report the first Indium Tin Oxide (ITO) electrochemical microsensor capable of accurately measuring Mn levels in human blood with cathodic stripping voltammetry (CSV). As shown in Fig. 1 (a), the ITO microsensor was developed by integrating a screen-printed carbon auxiliary electrode and an Ag/AgCl reference electrode on an ITO coated glass slide (1 cm × 4 cm). A circular ITO film with 3 mm diameter was exposed and used as the working electrode. To start electrochemical analysis, blood sample was first microwave digested with nitric acid and hydrogen peroxide to release Mn2+ bound to the proteins. The acid-digested blood sample was then titrated with sodium hydroxide to pH 5. Square wave cathodic stripping voltammetry (SWCSV) with optimized parameters was carried out to construct the calibration curve in the digested & pH adjusted blood sample with the Mn concentration ranging from 1.2 ppb to 25 ppb (confirmed by ICP-MS). The voltammogram in Fig. 1(b) shows an increasing trend of peak height and area with Mn concentration; and the calibration curve in Fig. 1(c) shows a sensitivity of 38.6 nC/ppb and linearity of 0.997 from the sensor’s measurements. We used the same stripping parameters, while applying a 3-point standard addition method, to determine the Mn concentration in two blood samples. The concentrations of 10.5 ppb and 26.3 ppb from our measurements lead to an average accuracy of 90% in comparison to the ICP-MS results of 8.9 ppb and 27.6 ppb. Four 150 µl sample droplets with a total volume of 600 µl were used in the measurement. Considering the 10X dilution from the blood digestion and pH adjustment process, only 60 µl of whole blood is needed to determine the Mn level with our approach. The favorable results and the small blood volume required in this work suggests the feasibility of point-of-care monitoring Mn in blood and is expected to be very useful for monitoring Mn exposure in vulnerable populations like children. Figure 1

Altered electrochemistry of amiloride drug on boron-doped diamond electrode: Rapid and selective detection in urine by square-wave cathodic stripping voltammetry for application in doping control

The amiloride (AMI) is a diuretic drug and has been illegally used in sports competitions. The development of simpler and faster analytical methods for AMI determination in urine samples is of interest of the World Anti-Doping Agency (WADA). In this context, we present a novel electroanalytical method for selective and sensitive detection of AMI in urine samples using a boron-doped diamond electrode (BDDE) with square-wave cathodic stripping voltammetry (SWCSV). Additionally, for the first time, we propose a complete electrochemical mechanism for all (six) presented redox processes of AMI. The determination of AMI is based on one of its reduction processes at the BDDE at -0.3 V (vs Ag/AgCl), which allows the electrochemical detection of this drug in urine without interference from ascorbic and uric acids. The analytical performance of the proposed method provides a linear range of 0.5 to 55.1 μmol L − 1 (r2=0.99) with LOD of 0.15 μmol L − 1, which is sufficiently low to assess urine sample containing AMI in anti-doping testing. Furthermore, the recovery studies in human urine samples were around 100% with a good stability (RSD < 2.0%) of the electrochemical response for AMI detection at BDDE by SWCSV, suggesting its application as a simple and rapid screening method for doping control of this drug.

Ultrasonic-Assisted Digestion of Cement and Clinker Samples for the Determination of Manganese by Square Wave Cathodic Stripping Voltammetry

Cement and clinker are complex samples and constitute a challenge for elemental analysis. Manganese, usually present in these matrices, can accumulate in bones, liver, the pancreas, kidneys, and brain and its monitoring is very important. This work presents an alternative method of sample treatment based on ultrasonic-assisted extraction for the determination of trace amounts of manganese in cement and clinker samples by square wave cathodic stripping voltammetry (SWCSV) on a gold working electrodes. The proposed extraction procedure occurs at room temperature inside closed vessels and uses 3.0 mol L−1 HCl solution, a less corrosive extractant compared to concentrated acids. Ultrasonic extraction was compared with conventional extraction by heating on hot plate and no significant differences between the two extraction methods were observed at the 95% confidence level. The possible use of H2O2 in the extraction process was evaluated but not used due to its interferences in the electrochemical determination of manganese. The SWCSV results obtained employing 0.20 mol L−1 H3BO3/0.10 mol L−1 KCl electrolyte at pH 6.5 produced two distinct linear regions of concentration for the analytical curve from 1.1 to 2.0 × 10−7 mol L−1 and from 2.0 to 3.2 × 10−7 mol L−1. The limits of detection and quantification were 3.1 × 10−8 mol L−1 and 9.8 × 10−8 mol L−1, respectively, and suitable for the proposed application. The results obtained by SWCSV were consistent with those obtained by flame atomic absorption spectrometry (FAAS) at the 95% confidence level.

Bis[2-(methacryloyloxy)ethyl] phosphate radiografted into track-etched PVDF for uranium (VI) determination by means of cathodic stripping voltammetry

We report the radiation grafting of bis[2-(methacryloyloxy)ethyl] phosphate (B2MP) through electron-beam onto PVDF films and through swift heavy ions (SHI) irradiations into the pores of track-etched PVDF membranes. Radiolytically produced radicals were studied using EPR. To adapt the radiation grafting protocol inside the nanopores of track-etched membranes, the electron-beam irradiated films at varying monomer concentrations, doses and solvent mixtures were first studied. It was found that track-etched membranes, even after 1 h of chemical treatment, do not require a post-etching irradiation to initiate free-radical polymerization of B2MP from remaining radiationinduced radicals. The presence of functional groups inside the nanopores of the membrane were examined using FTIR and XPS. After exposure of B2MP-g-PVDF membranes to a uranyl solution, XPS was also exploited to evidence of O2UO22+ trapping inside the membrane nanoporosity by tracking the presence of U 4f peak. The B2MP-g-PVDF membranes were converted into electrodes by depositing 35 nm of gold on each side through a mask. Detection of ppb concentrations (from 20 to 100 ppb) of uranyl by B2MP-g-PVDF membrane electrodes was demonstrated by means of square wave cathodic stripping voltammetry (SW-CSV). The limit of detection (LOD) was estimated to be 17 ppb (3σ−/ slope).

Compared arsenic removal from aqueous solutions by synthetic mixed oxides and modified natural zeolites

Layered Double Hydroxides of Mg–Al–Fe and their mixed metallic oxides of high specific surface area were synthesized by the coprecipitation method. A natural zeolite from a regional quarry with high clinoptilolite content was conditioned and modified. Initially, an acid treatment was applied and subsequently Fe(III) was incorporated by the wet impregnation method. Then the prepared solid materials were characterized by XRD, N2 adsorption–desorption at 77 K, SEM, DRS UV–Vis, and MP-AES to determine their physicochemical properties. Finally, the solid materials were evaluated as adsorbents for arsenic removal in water. The tracking of As and its species concentration at trace levels was carried out by cathodic stripping Square-wave voltammetry, which has proved to be a highly selective and sensitive electrochemical method. High levels of effectiveness in terms of removal were achieved, particularly with the natural zeolites and mixed oxides of highest iron content.

Multivariate cathodic square wave stripping voltammetry optimization for nitro group compounds determination using antimony film electrodes

The main goal of this paper is the optimization of the square wave voltammetric response of antimony film electrode (SbFE) to determine reducible nitro groups using response surface methodology (RSM). The SbFE was prepared on a glassy carbon electrode (GCE) while cathodic stripping square wave voltammetry (CSSWV) was used as detection technique. In this study, the optimization process of solution pH and 4,6-dinitro-o-cresol (DNOC) accumulation time was carried out using a Central Composite Design (CCD) while a Box–Behnken Design for SWV instrumental variables optimization. The two reduction current peaks were used as dependent variable to evaluate the performance of the system. For solution pH and DNOC accumulation time the optimization process considered only reduction current peak, while for SWV instrumental parameters (step, amplitude and frequency) both the relationship between current peak and standard deviation with the different factors were analysed, finally both designs were quantitatively described by a multivariate regression model through the RSM. Furthermore, the optimal parameter combinations were obtained by maximizing the reduction current peak and minimizing standard deviation within the studied experimental range. Under the optimal parameter combination, a linear calibration curve ranged from (1.0 to 15)×10−6molL−1 with a detection limit of 1.12×10−6molL−1 was obtained. The proposed analytical procedure was further applied to detect DNOC in natural water samples with satisfactory results.

Raman, X‐Ray Fluorescence Spectroscopies and Graphene Oxide Modified Screen Printed Electrodes to Identify the Pigments and Earth Present in Ancient Leather Samples

AbstractMicro‐Raman and X‐Ray Fluorescence combined with electrochemical techniques proved to be suitable for the unambiguous identification of the green pigment in a very deteriorated historical leather. The colouring matter resulted in a mixture of blue and yellow. Raman identified the blue indigo, whereas iron and arsenic were identified by XRF. The redox status of these two elements was investigated by Square Wave Cathodic Stripping Voltammetry (SWCSV). Results demonstrated the presence of As(III), probably As2S3 (orpiment), and Fe(III), characterising the red earths. The quantitative results obtained by SWCSV were also confirmed for Fe and As by ICP‐MS (Inductively Coupled Plasma Mass spectrometry). Voltammetric techniques, applied here for the identification of the redox status of the elements, contained in pigments, are useful to understand two important aspects: the chemical‐physical composition of the colors and the best strategy to be applied for the preservation of the pigments in ancient/deteriorated artwork objects.

Cathodic stripping square-wave voltammetry for assessing As(III) removal with synthetic mixed oxides

In this work, the adsorption of As(III) species from aqueous solutions onto mixed oxides (MOs) synthesized from layered double hydroxides (LDHs) has been assessed by cathodic stripping square-wave voltammetry (CS-SWV). The optimized electrochemical protocol involves the accumulation of arsenic for 60 s at −0.4 V, in presence of 0.5 mM Cu(II), 0.3 μM pyrrolidine dithiocarbamate (PDTC), and 0.9 M HCl, followed by a reductive scan to −1.0 V. A stable and well-defined peak was observed at −0.780 V, with a linear range that goes from 2 to 110 μg L−1 of As(III). A value of limit of detection (LOD) = 4 μg L−1 was calculated as three times the ratio between the standard deviation of the ordinate and slope of the linear regression curve. The presence of Cu(II) increases the signal of current and minimizes the effect of interfering species, while PDTC forms a complex that stabilizes the signal observed during the cathodic scan. Ternary LDHs and their MOs composed by MgAlFe were synthesized and characterized as potential filtering materials. X-ray photoelectron spectroscopy and UV-Vis diffuse reflectance analysis showed that the Fe(III) ions can be found in tetrahedral and octahedral coordination environments, while SEM micrographs evidenced the cluster formation and aggregates of particles when the Fe/(Fe+Al) molar ratio is increased. The capacity of MOs for removing As(III) has been studied at different contact times in a batch reactor, and in all cases, removals of As(III) above 75% were achieved.

Voltammetric analysis of disulfiram in pharmaceuticals with a cyclic renewable silver amalgam film electrode

Electrochemical properties of disulfiram, representative of highly significant bioactive compounds, were studied with a cyclic renewable silver amalgam film electrode (Hg(Ag)FE) using square wave cathodic stripping voltammetry (SWCSV). The influence of various factors such as pH, buffer concentration, buffer composition, and SWCSV parameters on current response was investigated. The optimum results in terms of signal shape and intensity were recorded in Britton--Robinson buffer (pH 7.5) at -0.5 V versus Ag/AgCl/3 mol L$^{-1}$ KCl. An elaborated electroanalytical procedure was used to determine disulfiram at the Hg(Ag)FE in the concentration range from 0.05 to 5.00 $\mu $M. Precision, repeatability, and accuracy of the method as well as the influence of possible interferences were ascertained. The detection and quantification limits were 11 nM and 37 nM, respectively. The applicability of the developed method was tested in the determination of disulfiram in the commercial formulation Anticol. Thin-layer chromatography with image processing software was used to validate the accuracy of the method.

“In-situ” antimony film electrode for the determination of tetracyclines in Argentinean honey samples

The main goal of this work is the application of an antimony film electrode (SbFE) prepared for the first time “in-situ” to determine organic compound as tetracyclines commonly used in Argentine for hive treatment. The SbFE was prepared on a glassy carbon electrode (GCE) and square wave cathodic stripping voltammetry (SWCSV) technique was used. The SWCSV parameters were optimized based on a Draper Lin small composite design. The SWCSV response was linear in the TCs concentration range from 0.40 to 3.00μM with a limit of detection (LOD) of 0.15μM. The proposed method is a good and simple alternative to the determination of tetracyclines in Argentinean honeys samples. Recovery experiments were performed using spiked honey samples with standard deviation values from 0.75% and 9.69%.

Theoretical and experimental study of the catalytic cathodic stripping square-wave voltammetry of chromium species

The electrocatalytic mechanism of Cr(III) reduction in the presence of diethylenetriaminepentaacetic acid (DTPA) and nitrate ions is studied theoretically and experimentally by using stripping square-wave voltammetry (SWV). Experimental curves are in excellent agreement with theoretical profiles corresponding to a catalytic reaction of second kind. This type of mechanism is equivalent to a CE mechanism, where the chemical reaction produces the electroactive species. Accordingly, the reaction of Cr(III)–H2O–DTPA and \( {\mathrm{NO}}_3^{-} \) would produce the electroactive species Cr(III)–NO3–DTPA and this last species would release \( {\mathrm{NO}}_2^{-} \) to the solution during the electrochemical step. In this regard, the complex of Cr(III)–DTPA would work as the catalyzer that allows the reduction of \( {\mathrm{NO}}_3^{-} \) to \( {\mathrm{NO}}_2^{-} \). Furthermore, it was found that the electrochemical reaction is quite irreversible, with a constant of ks = 9.4 × 10−5 cm s−1, while the constant for the chemical step has been estimated to be kchem = 1.3 × 104 s−1. Considering that the equilibrium constant is K = 0.01, it is possible to estimate the kinetic constants of the chemical reaction as k1 = 1 × 102 s−1 and k−1 = 1.29 × 104 s−1. These values of k1 and k−1 indicate that the exchange of water molecules by nitrate is fast and that the equilibrium favors the complex with water. Also, a value for the formal potential E°’ ≈ −1.1 V was obtained. The model used for simulating experimental curves does not consider the adsorption of reactants yet. Accordingly, weak adsorption of reagents should be expected.

Morphological characterization of ex situ prepared bismuth film electrodes and their application in electroanalytical determination of the biomolecules

A study on the preparation and characterization of the potentiostatically prepared bismuth films (BiFs), in order to obtain satisfactory electroanalytical tool, is presented. BiFs formed on glassy carbon were characterized by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The dependence of the BiFs properties upon electrolytes composition and electrochemical parameters are discussed and diagnostic criteria that allow estimation of the BiF morphology are proposed. Analytical performance data of the formed BiF electrodes were obtained by their application to the determination of glutathione (GSH) and folic acid (FA) using square-wave cathodic stripping voltammetry. The dependence of the analytical performance of the formed BiFs on their specific surface areas, along with their different morphology, is discussed. Adequate method and parameters for the electrochemical formation of optimal BiF, in order to fulfill the analytical requirements, are proposed. The best analytical performance was obtained with films formed from acetic buffer solution spiked with EDTA, as a consequence of the improved surface coverage and most arranged homogenous structure of the film. This electrode displays a linear response range toward GSH with estimated detection limit of 0.005 μM and sensitivity of 3.28 μA μM−1 for linear range of 0.01 to 0.1 μM. Also, the utilization of the BiF electrode for the determination of FA was demonstrated by direct electroreduction of FA.

Determination of metallothionein in Daphnia magna by modified square wave cathodic stripping voltammetry

Metallothioneins (MTs) are widely used as biomarkers in environmental studies. However, eliminating interfering factors for MT determination in vivo by electrochemical detection is difficult. In this study, NO3− and Cl− were found to negatively affect MT determination in Daphnia magna by square wave cathodic stripping voltammetry (SWCSV). The relevant mechanism was analyzed, and results were used to modify the original electrochemical testing parameters and environmental conditions. This modified SWCSV achieved accurate MT concentrations in D. magna, leading to detection limits as low as picomolar levels.

Stripping voltammetric determination of manganese in bioethanol

In this work, we describe the first electroanalytical method for manganese (Mn (II) determination in bioethanol based on square-wave cathodic stripping voltammetry (SWCSV) at a bare glassy-carbon electrode. Bioethanol is directly diluted in a Britton–Robinson buffer solution (pH4.0) and a stripping peak for Mn(II) is attained at approximately 0.9V (vs. Ag/AgCl). After optimizing SWCSV parameters (deposition potential and time, stirring speed, amplitude, frequency and step potential), the proposed method presented low relative standard deviation between injections (5.6%, n=10), low detection limit (16μgL−1) for a 300s deposition time and 40-fold dilution, a linear range between 3 and 175μgL−1, and adequate recovery values (90–110%) in fortified samples.

Bismuth film random array carbon fiber microelectrodes for determination of cysteine and N-acetyl cysteine

The electrochemical behaviors of bismuth at random array carbon fiber microelectrodes (RACFMEs) are studied by cyclic voltammetry. Obtained results indicate that dissolution of bismuth is facilitated in the presence of cysteine, by formation of bismuth cysteinate on electrode surface. Ex situ prepared bismuth film random array carbon fiber microelectrodes (BiF-RACFMEs) were applied for determination of cysteine and N-acetyl cysteine (NAC) by using square wave cathodic stripping voltammetry (SWCSV). Formation of bismuth cysteinate was performed at −0.4V, followed by bismuth reduction during cathodic sweep.The electrodes presented a linear response range toward cysteine and NAC, with estimated detection limits of 0.028μmolL−1 and 0.069μmolL−1, respectively. In the case of NAC two different linear concentration ranges of 0.1μmolL−1 to 1.0μmolL−1 and of 1.0μmolL−1 to 10.0μmolL−1 were obtained. The prepared BiF-RACFMEs have been successfully applied for determination of NAC in pharmaceutical samples (food supplement) with excellent recoveries.