Ação antioxidante da água catódica: estudos preliminares em sementes de café

Coffee seeds have limitations regarding to its conservation because of their sensitivity to desiccation and storage behavior. The establishment of a methodology for seed storage is difficult due to its deterioration. Deterioration can enhance the production of reactive oxygen species and cause lethal oxidative damage to plant tissues. The damage caused by harmful levels of free radicals can be softened by the action of endogenous or exogenous antioxidants. Recent research shows new antioxidative protection technologies, being cathodic protection a promising technique with relevant results in other recalcitrant species and even in other living organisms. Thus, the aim of this work was to verify the antioxidant effect of cathodic water in Coffea arabica L. seeds with the purpose of investigating a new technology to improve seed quality. The study was conducted at the Central Seed Laboratory, Department of Agriculture, at the Federal University of Lavras. Coffea arabica L. seeds were used. The study was conducted in two stages, in the first a preliminary analysis of the use of cathodic water was carried out in batches with different levels of quality. In the second it was evaluated the effect of light and of the imbibition period of the seeds in cathodic water. The seeds were immersed in distilled water and in cathodic water for eight distinct soaking periods, in absence and presence of light and then evaluated by physiological tests. It can be concluded that cathodic water can positively influence the physiological performance of the coffee seeds with poor quality, especially when embedded during periods between 4.5 to 7.5 hours in the absence of light.

Electrochemical feasibility study of methyl parathion determination on graphite-modified basal plane pyrolytic graphite electrode

A low-cost electrochemical method was developed for the determination of trace-level of methyl parathion (MP) based on the properties of graphite-modified basal plane pyrolytic graphite electrode (graphite-bppg). A combination of graphite-bppg with square-wave voltammetric (SWV) analysis resulted in an original, sensitive and selective electrochemical method for determination of MP pesticide in drinking water. The electrode was constructed and the electrochemical behavior of MP was studied. Immobilization is achieved via film modification from dispersing graphite powder in deionized water and through pipeting a small volume onto the electrode surface allowing the solvent to volatilize. The strong affinity of the graphite modifier for the phosphorous group of the MP allowed the deposition of a significant amount of MP in less than 60 seconds. The cyclic voltammetric results indicate that the graphite-bppg electrode can enhance sensitivity in current intensity towards the quasi-reversible redox peaks of the products of the cathodic reduction of the nitro group at negative potential (peak I = 0.077 V and peak II = –0.062 V) and that the cathodic irreversible peak (peak III = –0.586 V) in comparison with bare bppg electrode and is also adsorption controlled process. Under optimized conditions, the concentration range and detection limit for MP pesticide are respectively 79.0 to 263.3 mmol L-1 and 3.00 mmol L-1. The proposed method was successfully applied to MP determination in drinking water and the performance of this electrochemical sensor has been evaluated in terms of analytical figures of merit.

An alternative method for the simultaneous determination of copper and lead for quality control of sugar cane spirit using a nanotube-based sensor

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.

New voltammetry-based technique for the determination of tebuthiuron in crystal and brown sugar samples

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 |AgClsat 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.