The voltammetry is an important analytical technique and also useful for pKa determination. It is a usual procedure of this technique to employ inert electrolyte concentration 100 times higher than redox compound concentration further a pH buffer. However, the ionic strength changes with the solution pH. In this work, we study the consequences of this procedure by using a model system, aniline. A differential pulse voltammetry was used with a glass carbon electrode in 4.0 x 10-3 mol L-1 aniline, 0.04 mol L-1 Britton-Robinson Buffer, NaNO3 as inert electrolyte and pH from 2.0 up to 7.0. The first oxidation peak (0.67V ca.) was used. The pKa determination was performed by using intersection lines at Epeak versus pH. This method was also theoretically discussed for both the oxidant or reducing compound with Brönsted acid-base behavior. For the cited procedure, the ionic strength changed from 0.418 to 0.528 mol L-1, and the experimental pKa (5.691) was far from theoretical one (4.722), still a good fit of lines to experimental data. Using the correct procedure, the experimental pKa (4.938) was near the theoretical one. Therefore, we have proved the need for a more careful adjust of ionic strength in this application.

This study aimed to use a differential pulse voltammetric (DPV) assay, based on the electroreduction of oxygen, to evaluate the antioxidant capacity of pequi pulp. The results were expressed in coefficient of antioxidant capacity (K), at different pH values and in trolox equivalent antioxidant capacity (TEAC), and were compared to the 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) spectrophotometric assays. The principal component analysis showed higher K for pequi pulp extract and pH tending to 7.15. The antioxidant capacity was related to the presence of gallic acid in its composition. Regarding the TEAC value, the best result was obtained by the DPV test (53.43 ± 5.14 µmol trolox g-1 pulp). The pequi pulp showed antioxidant capacity, compared to the standard antioxidant compounds evaluated. It was concluded that the voltammetric protocol was efficient to assess the total antioxidant capacity of pequi pulp and can be an alternative to conventional spectrophotometric assays, for the analysis of food matrices.

One new methodology for analysis of the antimicrobial oxolinic acid (OXA) based on adsorptive stripping voltammetry (AdSV) in carbon paste electrode (CPE) was developed and applied in untreated pond water sample. Cyclic voltammetry (CV) indicated that an irreversible anodic process occurs in KOH solution as supporting electrolyte. Quantification of the antimicrobial was carried out by differential pulse adsorptive stripping voltammetry (DPAdSV) at potential of deposition (ED) +1.05 V for 45 s to examine OXA adsorption on the surface of CPE. The limits of detection (LOD) and quantification (LOQ) of the method for OXA analysis were determined. The values of LOD were 0.0570 and 0.512 mg L-1 in absence of matrix and in the water sample, respectively, and the corresponding values of LOQ were 0.192 and 1.707 mg L-1, respectively. The apparent recovery percentage for different concentrations of OXA in natural waters ranged between 98.4 and 109%.

In this work, a new and sensitive electroanalytical methodology was developed and validated to quantify sulfentrazone in soil samples. Sulfentrazone was initially characterized qualitatively using cyclic voltammetry (CV). Its oxidation occurred by diffusion (mass transport) on a glassy carbon electrode (GCE) via irreversible transfer of one electron close to a peak potential of +0.936 V vs. Ag|AgCl, 3.0 mol L-1 KCl, in 0.10 mol L-1 KOH. Differential-pulse voltammetry (DPV) was the most sensitive and selective technique, with limits of detection (LOD) of 1.94 and 2.19 mmol L-1 and limits of quantification (LOQ) of 6.46 and 7.31 mmol L-1, in the absence and presence of soil matrix, respectively. The reproducibility of the method ranged between 2.65 and 4.2%, with intermediate precision between 5.32 and 10.9%. The recovery rate ranged between 88.5 and 103%. Additionally, the accuracy of the electroanalytical method was validated by comparing the results with data from a standard analytical methodology of high-performance liquid chromatography (HPLC/UV-Vis).

O açúcar é amplamente consumido em todo o mundo e o Brasil é o maior produtor, consumidor e exportador deste produto. Para garantir o bom desenvolvimento e produtividade das culturas de cana de açúcar, é necessário aplicar grandes quantidades de agrotóxicos, principalmente herbicidas e pesticidas. O herbicida tebuthiuron (TBH) impede a pré e pós-emergência das plantas daninhas infestantes nas culturas de cana de açúcar. Considerando que é importante para garantir a segurança alimentar da população, este trabalho propõe um método confiável para analisar TBH em matrizes de açúcar (mascavo e cristal), usando voltametria de onda quadrada (SWV) e voltametria de pulso diferencial (DPV) em eletrodo de carbono vítreo e investigar o comportamento eletroquímico do herbicida por voltametria cíclica (CV). Os nossos resultados sugerem que TBH ou o produto da sua reação com o eletrólito de suporte é oxidado através da transferência irreversível de um elétron entre o analito e eletrodo de trabalho, a um potencial de cerca de +1,16 V vs. Ag|AgCl sat em 0,10 mol L-1 KOH como solução de eletrólito de suporte. Tanto DPV quanto SWV são satisfatórios para a análise quantitativa do analito. DPV é mais sensível e seletiva, com limites de detecção de 0,902, 0,815 e 0,578 mg kg-1, e limite de quantificação de 0,009, 0,010 e 0,008 mg kg-1, na ausência da matriz, e na presença de matriz de açúcar cristal e mascavo, respectivamente. Reprodutibilidade situou-se entre 0,53 e 13,8%, a precisão variou entre 4,14 e 15,0%, e a recuperação manteve-se entre 84,2 e 113% para DPV conduzido na ausência e na presença da matriz de açúcar cristal, respectivamente.

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 square wave voltammetry (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. Both DPV and SWV are satisfactory for the quantitative analysis of the analyte. DPV is more sensitive and selective, with detection limits of 0.902, 0.815 and 0.578 mg kg-1, and quantification limits of 0.009, 0.010 and 0.008 mg kg-1 in the absence of the matrix and in the presence of crystal and brown sugar matrix, respectively. Repeatability lay between 0.53 and 13.8%, precision ranged between 4.14 and 15.0%, and recovery remained between 84.2 and 113% in the case of DPV conducted in the absence of matrix and in the presence of the crystal sugar matrix, respectively.

Um método eletroanalítico foi desenvolvido para determinação simultânea de íons cobre e chumbo em cachaça empregando eletrodo de pasta de carbono modificado com ácido ascórbico e nanotubos de carbono (CPE-AaCNT). A técnica de voltametria de onda quadrada (SWV) com redissolução anódica foi empregada e otimizada com relação aos seguintes parâmetros: frequência (50 Hz), amplitude (100 mV) e incremento de varredura (9 mV). As curvas analíticas apresentaram intervalo linear de 0,09 a 7,00 mg L- 1 para o chumbo e para o cobre. Os limites de detecção foram de 48,5 e 23,9 µg L- 1 para o chumbo e o cobre, respectivamente. O método desenvolvido foi aplicado na determinação simultânea de chumbo e cobre em cinco amostras comerciais de cachaça. Os resultados apresentaram-se concordantes com os obtidos por F AAS/GF AAS (espectrometria de absorção atômica com chama/espectrometria de absorção atômica com forno de grafite) e revelaram que CPE-AaCNT podem ser empregados com êxito na quantificação de cobre e chumbo em amostras comerciais de cachaça.

The development of an electroanalytical method for simultaneous determination of copper and lead ions in sugar cane spirit (cachaça) using carbon paste electrode modified with ascorbic acid and carbon nanotubes (CPE-AaCNT) is described. Squarewave voltammetry (SWV) with anodic stripping was employed, and this technique was optimized with respect to the following parameters: frequency (50 Hz), amplitude (100 mV) and scan increment (9 mV). The analytical curves were linear in the range from 0.0900 to 7.00 mg L- 1 for lead and copper. The limits of detection were 48.5 and 23.9 µg L- 1 for lead and copper, respectively. The developed method was applied to the simultaneous determination of copper and lead in five commercial samples of sugar cane spirit. The results were in good agreement with those obtained by F AAS/GF AAS (flame atomic absorption spectrometry/graphite furnace atomic absorption spectrometry) and showed that CPE-AaCNT can be successfully employed in the simultaneous determination of these metals in real sugar cane spirit samples.