SQUAREWAVEVOLTAMMETRY. SECOND PART: APPLICATIONS. The aim of this work is to discuss some selected applications of squarewavevoltammetry published in the last five years. The applications focused here cover several electroanalytical fields such as: determination of pesticides; molecules with biological activity; metals and other environmental pollutants. Special attention is given to the work developed in the Grupo de Materiais Eletroquímicos e Métodos Eletroanalíticos – IQSC – USP concerning the utilization of squarewavevoltammetry, with different kinds of electrodes, for the determination of pesticides in natural waters and active principles in pharmaceutical formulations. The new methodology is simple, fast and sensitive when compared with the traditional ones such as chromatography and spectrophotometry. The satisfactory results obtained provide alternative procedures for the quality control of drugs and the monitoring of pesticides in natural environments.
ELECTROANALYTICAL DETERMINATION OF 4-CHLOROPHENOL BY SQUAREWAVEVOLTAMMETRY ON BORON- DOPED DIAMOND ELECTRODES. The anodic voltammetric behavior of 4-chlorophenol (4-CF) in aqueous solution has been studied on a Boron-doped diamond electrode using squarewavevoltammetry (SWV). After optimization of the experimental conditions, 4-CF was analyzed in pure and natural waters using a Britton-Robinson buffer with pH = 6.0 as the supporting electrolyte. Oxidation occurs at 0.80 V vs Ag/AgCl in a two-electron process controlled by adsorption of the species. The detection limits obtained were 6.4 µg L -1 in pure water and 21.5 µg L -1 for polluted water taken from a local creek, respectively. The
respostas obtidas após a aplicação de uma série de pulsos sobre- postos em um mesmo degrau de potencial de uma escada de poten- ciais. Todas as variações de potencial eram realizadas nos domíni- os do intervalo de eletroatividade do sistema redox de interesse. Este método foi chamado de “Integrated Multiple SquareWaveVoltammetry (IMSWV)” e se mostrou mais sensível que a DIMPP, por ser mais rápido e apresentar maior minimização das correntes capacitivas.
ELECTROANALYTICAL STUDY OF THE PARAQUAT HERBICIDE IN AQUEOUS SOLUTION BY SQUAREWAVEVOLTAMMETRY USING ULTRAMICROELECTRODES. The electrochemical behavior of paraquat on Pt, Au and carbon fiber ultramicroelectrodes were studied in laboratory samples by squarewavevoltammetry at high frequencies. The results showed two reversible peaks for paraquat reduction, in agreement to the literature data. The first peak was associated to the reduction of paraquat molecule in solution, with the further adsorption of the intermediate on the electrode surface. This adsorbed species undergoes to electroreduction in a reaction associated to the second voltammetric peak. The variation in pH and squarewave parameters showed the best conditions to reduce paraquat as pH 5.0, frequency as high as 1000 s -1 , scan increment of 2 mV and
UTILIZATION OF DISPOSABLE POLYPROPYLENE FLASKS FOR PRE-TREATMENT OF WATER SAMPLES FOR DETERMINATION OF LEAD, COPPER AND MERCURY BY SQUAREWAVEVOLTAMMETRY. In this work a simple and versatile procedure is described for treating water samples using small polypropylene (PP) vials (4 mL) for determining heavy metals by squarewavevoltammetry (SWV). This procedure involves treatment with nitric acid (0.2 mol L -1 ) and boiling in a water-bath (~ 100 o C).
SQUAREWAVEVOLTAMMETRY. PART I: THEORETICAL ASPECTS. The theoretical aspects of squarewavevoltammetry were discussed. Reversible, irreversible and quase-reversible electrode reactions were analyzed and the correlations between parameters like frequency, period, squarewave potential and amplitude were showed. In this way, diagnostic relationships allow to characterize the electrode process. The analytical applications were discussed in base of the increment in the analytical response (current) due to the characteristics of the developed equations and the unique mode of collecting the electrode response, i.e., the direct and reverse signals. Finally, recent advances in the basic theory, as the applications to the hydrodynamic electrode and the ultramicroelectrode were also analyzed, and the multiple pulses squarewavevoltammetry was also introduced.
O objetivo deste trabalho é a determinação de íons Mn(II) em amostras de material particulado no ar do ambiente de trabalho de uma fundição de liga de latão empregando Voltametria de Redissolução Catódica por Onda Quadrada (“SWCSV – SquareWave Cathodic Stripping Voltammetry”) com eletrodo de diamante dopado com boro, validando os resultados por comparação com ICP OES, técnica adota- da pela “National Institute of Organization Safety (NIOSH)” para aná- lises de metais em amostras de ar 8 .
The SquareWaveVoltammetry (SWV) is a pulse technique that offers the advantage of great speed and sensitivity. The excitation signal in SWV is obtained applying a series of forward and reverse pulses super- imposed onto a constant height staircase of potential to the working electrode. The current is sampled twice in each wave cycle: once at end of the forward pulse and once at the end of the reverse pulse. The signal is given by the difference between these two currents. 21-23 This paper
In the family of pulse techniques square-wave voltamme- try appears to be one of the most advanced electroanalytical techniques (17). This technique is attributed with unique advantages, such as: high frequency and amplitude, solitary approach in the current-sampling procedure, as well as the effective ability to discriminate the capacity current. Thus, for developing a particular absorptive stripping voltammetric method for determination of miscellaneous species, square- wavevoltammetry is most frequently a technique of choice.
Sugar is widely consumed worldwide and Brazil is the largest producer, consumer, and exporter of this product. To guarantee proper development and productivity of sugar cane crops, it is necessary to apply large quantities of agrochemicals, especially herbicides and pesticides. The herbicide tebuthiuron (TBH) prevents pre- and post-emergence of infesting weed in sugarcane cultures. Considering that it is important to ensure food safety for the population, this paper proposes a reliable method to analyse TBH in sugar matrixes (brown and crystal) using squarewavevoltammetry (SWV) and differential pulse voltammetry (DPV) at bare glassy carbon electrode and investigate the electrochemical behavior of this herbicide by cyclic voltammetry (CV). Our results suggest that TBH or the product of its reaction with a supporting electrolyte is oxidized through irreversible transfer of one electron between the analyte and the working electrode, at a potential close to +1.16 V vs. Ag |AgCl sat in 0.10 mol L -1 KOH as supporting electrolyte solution.
In this work, the graphite-PU electrode per- formance in an analytical procedure for the quan- tification of hydroquinone in photographic develop- ers using squarewavevoltammetry (SWV) was developed. In order to obtain the best analytical response, parameters, such as frequency, pulse amplitude and step potential, were optimized.
This paper describes the use of squarewavevoltammetry for the electroanalytical determination of picloram in aqueous media. The reaction was found to occur via an irreversible mechanism involving the transference of four electrons, with the reagent adsorbed in the electrode surface. The practical application was carried out with spiked water samples originated from purified water and from three different local creeks, two of which are highly polluted with industrial and domestic effluents. The calculated detection limits ranged from 11 (for pure and unpolluted waters) to 39 ppb for the most contaminated sample. These low values indicate that such methodology can be conveniently applied in trace analysis.
Abstract: The determination of the herbicide ametryne in acid solution was performed using squarewavevoltammetry and a static drop mercury electrode. The electroredution reaction proceeds through a completely irreversible mechanism with the diffusion of the electroactive specie being the rate determining step. It was observed a previous protonation of the reagent molecule followed by the transference of two electrons. The linearity of peak current with concentration allows to calculate a detection limit of 0,1 mg L -1 (0,1 ppb). This value is adequate for the analysis of herbicide contamination (e.g., in drinking water).
A carbon-paste electrode modified with the polymer poly(vinylpyrrolidone) was evaluated through electrochemical studies and the electroanalytical determination of quercetin. For this electrode, cyclic voltammograms of quercetin showed three oxidation peaks at +0.32, +0.78 and +1.04 V. The electro-oxidation associated with the first peak leads to the formation of the corresponding ortho-quinone, which can be reduced under favorable experimental conditions. Under such conditions, the reaction is quasi-reversible and the process is diffusion-controlled. This behavior was exploited for the electroanalytical determination of quercetin by square-wavevoltammetry. The calibration curve was linear in the concentration range of 0.5 to 5.5 µmol L –1
The proposed amperometric sensor was evaluated using analyses of enriched samples of human serum. The measurements were analyzed by squarewavevoltammetry (SWV). The results obtained were found to be close to the reference value, indicating that the system analyzed showed no matrix effect (Table 3). The method used in the determination of diclofenac in the matrices analyzed was the standard addition. In these analyses standard solution aliquots are added to the electrochemical cell, and the current obtained is extrapolated in the analytical curve, in the order to obtain the respective concentration of diclofenac in the sample (Figure S6).
versatile because it enables automated construction of external calibration curves, in-line standard addition and in-line dilution. With SI, the consumption of sample and reagents is greatly reduced because the flow is programmed and bidirectional, so that volumes of reagents are preset (contrary to continuous flow analysis in which the solutions are continually pumped toward the detector). Squarewavevoltammetry (SWV) is an electrochemical technique which provides high sensitivity for the determination of pesticides, reaching detection limits similar to those obtained by high performance liquid chromatography (HPLC) with ultraviolet detection (UV), usually employed to determine these compounds in water, soil and food. 12-16 The greatest