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Abstract: The electrochemical oxidation of flavonoid butein is studied at glassy carbon electrodes in phosphate and citrate buffer solutions of different pH values, and 1M perchloric acid aqueous solutions by cyclic and square wave voltammetries. The oxidation peak corresponds to the 2e−, 2H+ oxidation of the 3,4-dihydroxy group in B ring of butein, given the corresponding quinone species. The overall electrode process shows a quasi-reversible behavior and an adsorption/diffusion mixed control at high butein bulk concentrations. At low butein concentrations, the electrode process shows mainly an adsorption control. Butein surface concentration values were obtained from the charge associated with the adsorbed butein oxidation peaks, which are in agreement with those values expected for the formation of a monolayer of adsorbate in the concentration range from 1 to 5μM. Square wave voltammetry was used to perform a full thermodynamic and kinetics characterization of the butein surface redox couple. Therefore, from the combination of the “quasi-reversible maximum” and the “splitting of the net square wave voltammetric peak” methods, values of (0.386±0.003) V, (0.46±0.04), and 2.7×102 s−1 were calculated for the formal potential, the anodic transfer coefficient, and the formal rate constant, respectively, of the butein overall surface redox process in pH4.00 citrate buffer solutions. These results will be then used to study the interaction of butein, and other flavonoids with the deoxyribonucleic acid, in order to better understand the potential therapeutic applications of these compounds. [Copyright &y& Elsevier]

Abstract: The electrochemical oxidation of fisetin (FIS) on glassy carbon (GC) electrodes is studied in 15% dimethyl sulfoxide (DMSO) +85% pH 4.00 and 7.00 buffer solutions by cyclic (CV) and square-wave (SWV) voltammetries. The first oxidation peak of FIS showed an adsorption/diffusion mixed control, when studies were performed in solutions in the presence of FIS. Therefore, the FIS adsorption on the GC electrode surface could be inferred from cyclic voltammograms recorded in supporting electrolyte solutions, where a quasi-reversible redox couple was defined at both pH values. These findings show that both the reactant and the product of the electrode process are adsorbed on the electrode surface, being the surface redox couple slightly better defined at pH 4.00 than 7.00. The Frumkin adsorption isotherm was the best to describe the specific interaction of FIS with GC electrodes, using a fitting procedure of experimental fractional surface coverage (θ) vs. FIS bulk concentration (). Moreover, we used the SWV to obtain a full characterization of the surface redox couple, applying the combination of the “quasi-reversible maximum” and the “splitting of the net voltammetric peak” methods. Values of (0.340±0.003) V, 41s−1, and (0.49±0.04) were determined for the formal potential, the formal rate constant, and the anodic transfer coefficient, respectively. [Copyright &y& Elsevier]

Abstract: A novel conducting polymer of polynaphthidine, poly(NAP), was synthesized electrochemically by direct anodic oxidation of naphthidine in aqueous media. The yield of the electropolymerization reaction depends on the temperature and pH of the solution. It was possible to differentiate two working regions: I (for pH<0.5 and all temperatures) where the film yield tends to zero and II (for approximately 2.015°C) where the film production is maximum. Therefore, the naphthidine electrooxidation mechanism was studied under experimental conditions of region I by cyclic (CV) and square wave voltammetries (SWV) as well as by controlled potential electrolysis. The experimental conditions of region II were chosen to obtain the poly(NAP). The electrochemical response of the film was investigated in pH 1 HClO4 +0.1M NaClO4 electrolyte solution by CV and SWV. A plot of I p,n/f vs. f from SW voltammograms showed the so-called “quasi-reversible maximum”. Formal potential, formal rate constant and anodic transfer coefficient for the surface redox process were also evaluated from the SWV. The poly(NAP) is insoluble in common organic solvents and shows electrochromic behaviour. Its probable structure was determined by FTIR spectroscopy. [Copyright &y& Elsevier]

The article cites a research study that seeks to determine synthetic antioxidants in vegetable oils by using square wave voltammetry (SWV) on ultramicroelectrodes (UME). SWV is a voltammetric phenomenon that is currently being used in a wide variety of analytical chemistry fields. In previous studies, the researchers have implemented the ectrochemical techniques to determine synthetic antioxidants in edible vegetable oils. But in the present experiment the researchers propose an experiment that introduces SWV using UME as an electroanalytical technique to determine tert-butylheroxy-toluene added as a synthetic antioxidant to vegetable oils.

The electrooxidation of altenuene (ALT), one of the mycotoxins of the Alternaria alternata genus, on a glassy carbon disk electrode is studied for the first time by using cyclic and square wave voltammetry. From the electrochemical responses, a complex reaction mechanism could be inferred. Values of 1.06×10−5 cm2 s−1, 1.116 V and 2 were determined for the diffusion coefficient, the apparent formal potential and the electron number, respectively, for the overall electrode process by convolution analysis of linear scan voltammograms. Square wave voltammetry was used to generate Ip versus cALT* calibration curves for this fungal metabolite. A detection limit of 4.0×10−7 M was determined for a 2:1 signal to noise ratio. The acid dissociation constant for ALT was determined from conventional UV–vis spectrophotometric measurements. Experimental variations of absorbance as a function of pH at a given wavelength were fitted by using the exact equation that describes the system. Good agreement between the experimental absorbance versus pH plots and the curves generated by the fitting process was found. [Copyright &y& Elsevier]

This paper describes the development of a simple and sensitive electrochemical immunosensor (EI) to quantify estrone (E) in water samples. This EI does not require the sample pre-treatment, to label neither the antigen nor the antibody, and its detection format is based on the fact that E is co-substrate of the horse radish peroxidase (HRP). Therefore, the EI was constructed by immobilization of the anti-E monoclonal antibody (mAbE) on a glassy carbon electrode (GCE) modified with gold nanoparticles (AuNPs) electro-synthesized on a 1-naphtylamine polymer (pNap) film. This format reduced significantly the time of EI preparation. Water samples were spiked with known E concentrations, and then incubated on mAbE-AuNPs-pNap-GCE disk electrode. The electrochemical response was proportional to the amount of pyrocatechol (H 2 Q), another enzyme co-substrate, and inversely proportional to the amount of E presents in water samples. The immunosensor showed a linear range from 8 × 10 − 2 to 2 × 10 4 pg mL − 1 . The limit of detection (LOD) was 0.061 pg mL − 1 . Recovery percentages obtained were very good, with values of 98.20, 105.50, and 100.85% for 50, 100 and 200 pg mL − 1 , respectively. Tests were also conducted to evaluate the cross-reactive of E with other hormones of similar structure such as 17β-estradiol, progesterone and estriol. The EI showed a high selectivity to determine E in the presence of these hormones. Thus, this EI is an attractive tool to determine E in water samples. [ABSTRACT FROM AUTHOR]

We present for the first time a novel analytical method based on a model of three-way calibration using second-order data generated from the combination of records of forward (oxidation) and reverse (reduction) currents using a glassy carbon electrode modified with a dispersion of electrochemically reduced graphene oxide (GCE/RGO) as the working electrode, which can be obtained from a square wave voltammetry single experiment. This methodology was used for the simultaneous determination of ascorbic (AA) and uric (UA) acids, and dopamine (DO) in the presence de glucose (interfering species) in lyophilized human serum samples. The serum samples have analyte different concentration levels (normal and pathological levels). The forward and reverse currents were pre-processed using AsLS and COW, to generate the second order data and finally the data were modeled with the U-PLS algorithm. Recovery studies were made in order to validate the proposed method. Recovery percentages between 92.4 and 120% were obtained. The present method has the advantage to generate second order data through a simple voltammetric experiment. Among the advantages of the proposed method can be mentioned speed, easy data acquisition and the possibility of using modified electrodes with nano-structures. [ABSTRACT FROM AUTHOR]

Abstract: The adsorptive accumulation of rutin (RU) at glassy carbon (GC) electrodes in 10% ethanol+90% 1moldm−3 HClO4 aqueous solution is studied by using cyclic (CV) and square wave (SWV) voltammetries. The Frumkin adsorption isotherm best described the specific interaction of rutin with carbon electrodes. By fitting the experimental data, values of −31.9kJmol−1 and 0.54±0.02 were obtained for the Gibbs free energy of adsorption and the interaction parameter, respectively. SWV fully characterized the thermodynamics and kinetics of the surface redox process, using a combination of the “quasi-reversible maximum” and the “splitting of SW peaks” methods. Average values of 0.644±0.003V and 0.44±0.02 were obtained for the formal potential and the anodic transfer coefficient, respectively. Moreover, a formal rate constant of 6.1×102 s−1 was obtained. SWV was also employed to generate calibration curves. The lowest concentration of RU experimentally measured for a signal-to-noise ratio of 3:1 was 2×10−8 moldm−3 (12ppb). [Copyright &y& Elsevier]

Abstract: A simple electroanalytical method using square wave voltammetry at a Pt band ultramicroelectrode to perform a qualitative and quantitative analysis of different synthetic antioxidant mixtures permitted by official regulations in edible oils is proposed. The methodology was based on the comparison of voltammetric signals obtained in acetonitrile+0.1M (C4H9)4NF6P with those recorded in the same reaction medium when different aliquots of (C4H9)4NOH were added to allow a qualitative differentiation between antioxidants. Firstly, studies on solutions prepared from commercial reagents were carried out. Then, the results obtained were transferred to the analysis of a real matrix, i.e., an edible olive oil. From real samples spiked with a known amount of different synthetic antioxidant mixtures, we could deduce the presence of these antioxidants by comparing results obtained in the neutral medium with those obtained after the successive addition of base. The standard addition method was used to quantify the individually spiked synthetic antioxidants in the real sample. Recovery percentages were between 88% and 118%. The reproducibility was 1.5%, 3.1%, 4.1% and 4.1% in ACN+0.1M TBAHFP and 1.5%, 4.6%, 6.6% and 2.5% in Bz/EtOH (1:2)+0.1M H2SO4 for TBHQ, BHA, BHT and PG, respectively. The repeatability was 1% for PG in both media. These parameters show a good system performance. [Copyright &y& Elsevier]

Abstract: The adsorption of progesterone (P4) on the glassy carbon (GC) electrode surface by mean of square wave stripping voltammetry measurements is studied. A cathodic peak is obtained at −1.65V (vs. ECS) in pH 8 buffer solution after accumulation onto GC surface at open circuit. Peak current variations with the accumulation time, P4 concentration and temperature are presented. The adsorption is characterized by a nonlinear pseudosigmoid temperature dependence of the Gibbs free energy, which reveals that the adsorption strength is increased at higher temperatures. During the adsorption of P4, strong lateral interactions are developed between neighboring adsorbates, which are severely weakened as the temperature increases. The Frumkin isotherm is the model which best fit to experimental results. Values of the Gibbs free energy, enthalpy and entropy of adsorption are calculated. Also, the apparent heterogeneous rate constant for the electron transfer reaction of adsorbed species is determined. [Copyright &y& Elsevier]

• A novel electroanalytical method was developed to determine CAR in OEO samples. • Second-order cyclic voltammetry data were generated varying the scan rate. • The CAR determination was performed in presence of thymol as a potential interferent. • MCR-ALS was successfully used to obtain the second order advantage. A novel analytical method using voltammetric second-order modeling based on multivariate curve resolution-alternating least-square (MCR-ALS) is presented for the first time for the quantitation of carvacrol (CAR) in oregano essential oils (OEO). The second-order cyclic voltammetry data were generated on the basis that CAR shows a diffusional system. Thus, the scan rate (v) was used as a second instrumental mode and cyclic voltammograms at different v were acquired for a single sample, generating the second-order data. CAR determination was performed in presence of thymol, included as a potential interferent. Results demonstrated that MCR-ALS successfully exploited the second-order advantage and the recoveries were not statistically different than 100%. The limits of detection and quantitation were estimated using the MCR-ALS which were 6.27 × 10−5°mol°L−1°and 1.90 × 10−4°mol L−1, respectively. Finally, the developed methodology was implemented to quantify of CAR in OEO samples. [ABSTRACT FROM AUTHOR]