Estudo da degradação fotocatalítica de dimetil dissulfeto: avaliação estatistica do efeito do pH da temperatura e concentração do contaminante orgânico

This work aimed to assess the photocatalytic degradation of a model odor compound (dimethyl disulfide, DMDS), found in liquid and gaseous wastes of plants for processing poultry byproducts. The effect of pH and temperature on adsorption and photocatalytic degradation was evaluated through factorial experimental designs. The results suggest the presence of an optimum region for adsorption, at 45.0 ºC and pH 4.0. In the photocatalytic runs an optimum for temperature and pH was also observed. At 45 ºC and pH 4.0 the removal of DMDS was 99% after 60 min of irradiation.

Hidrólise do óleo de Azadirachta indica em água subcrítica e determinação da composição dos triacilglicerídeos e ácidos graxos por cromatografia gasosa de alta resolução a alta temperatura e cromatografia gasosa de alta resolução acoplada à espectrometria de massas

The development of modern analytical tools plays an important role in quality control. The main purpose of this study was to explore the use of subcritical water as a versatile analytical tool, employed simultaneously as a reagent and solvent, as well as the application of high temperature-high resolution gas chromatography (HT-HRGC) to develop a procedure for the analysis of triacylglycerides and fatty acids in Azadirachta indica A. Juss. (Neem) oil without the need for solvents, chemical reagents, or catalytic agents. The developed method presented satisfactory results and is in agreement with the concepts of Green Analytical Chemistry (GAC).

Possibilidades e limitações no uso da temperatura em cromatografia líquida de fase reversa

High-temperature liquid chromatography (HTLC) is a technique that presents a series of advantages in liquid phase separations, such as: reduced analysis time, reduced pressure drop, reduced asymmetry factors, modified retentions, controlled selectivities, better efficiencies and improved detectivities, as well as permitting green chromatography. The practical limitations that relate to instrumentation and to stationary phase instability are being resolved and this technique is now ready to be applied for routine determinations.

Comparação da labilidade de metais empregando voltametria, difusão em filmes finos por gradiente de concentração (DGT) e modelo computacional

Speciation of metals in a synthetic freshwater was comparatively evaluated using Anodic Stripping Voltammetry, Diffusive Gradients in Thin Films and a Chemical Equilibrium Model. The labile fractions of Cu and Zn quantified by DGT were similar to the ones measured by ASV. The labile species of Cd and Pb could not be determined by both experimental methods due to the formation of inert complexes with organic ligands in the sample. Despite the differences among the methods, the speciation results obtained by the use of DGT and ASV agreed well with predictions made by the chemical equilibrium model.

Influência da temperatura, umidade e profundidade do solo na persistência do diurom e sulfato de endossulfam em um solo tropical

The influence of temperature (30 and 40 ºC) and soil humidity (20, 50 and 70% of water holding capacity) on the degradation of the herbicide diurom and the endosulfan metabolite, endosulfan sulfate was studied under laboratory conditions, in different soil layers (0-30, 30-38 and 38-83 cm) of an Oxisol (Yellow Latosol) collected in an agricultural area of Mato Grosso State, Brazil. Endosulfan sulfate was rapidly degraded under lower soil humidity, higher temperature and deeper soil layers. For diurom the opposite was observed as a consequence of its higher water solubility and lower soil sorption coefficient.

Um sistema microcontrolado para o monitoramento on-line, in situ e remoto de pH, condutividade e temperatura de águas

A portable microcontrolled system is proposed to monitor conductivity, temperature and pH in on-line, in situ and remote way from a water reservoir faraway 200 m. The system comprises two modules: one for data reception (located in laboratory) and another for data acquisition/transmission (located near water reservoir). It uses a microcontroller and a transceiver to remote data transmission/reception by radio frequency. Variations of water parameters were simultaneously monitored without interruption during a period of ten hours with a relative error about 4.0 %. The developed system showed simple, stable, accurate, robust and low-cost to determine parameters of water in field.

Variación del grado de avance de reacción en sistemas cerrados en equilibrio químico que modifican la temperatura a volumen constante

In this paper it is presented a thermodynamic analysis that aims to find the mathematical expression of the variation of extent of reaction with the infinitesimal variation in the temperature at constant volume of a chemical equilibrium mixture. The goal of this paper is to establish an alternative approach to avoid both the Le Chatelier's principle and the problems that emerge when trying to apply its qualitative statements. This attempt is based on the laws of thermodynamics.

Capacidade de oxidação como índice de estabilidade da matéria orgânica de sedimentos de acordo com gradiente fluvial-estuarino do rio Paraíba do Sul

The hummus composition and it redox properties have been used to evaluate the organic matter quality from natural systems. The objectives of this study were the fractionation of the organic matter and the determination of the oxidation capacity of humic acids to evaluate the organic matter quality of sediments from a gradient fluvial-estuarine in the Brazilian Southeast. The carbon/nitrogen and humic acid/fulvic acid relationships of the organic matter and of the oxidation capacity of humic acids were positively correlated and followed the order: estuarine bordered mangroves ≅ fluvial bordered urban center and pasture > estuarine bordered pasture ≅ marine.

Efeito da temperatura do ar de secagem sobre o teor e a composição química do óleo essencial de Pectis brevipedunculata

Leaves and flower heads of P. brevipedunculata were submitted to four drying-air temperatures (room temperature, 40, 50 and 60 ºC). Room temperature (approximately 30 ºC) and higher temperature drying (50 and 60 ºC) had a deleterious effect on the essential oil content. The recommended drying-air temperature for the species is 40 ºC for it results in the same amount of essential oil observed in fresh cut plants. Overall, 13 components accounting for more than 92% of the total composition were identified. Citral was the major component, followed by α-pinene and limonene. The essential oil showed high toxicity against Artemia salina larvae.

Dinâmica oscilatória em sistemas contendo bromato e 1,4-ciclo-hexanodiona em meio ácido: I. Efeito da temperatura

We present in this work the influence of temperature on the dynamics of homogeneous chemical systems containing bromate and 1,4-cyclohexanedione (1,4-CHD) in acidic media. In particular, the following systems were studied: bromate/1,4-CHD/acid, bromate/1,4-CHD/ferroin/acid and bromate/1,4-CHD/trisbipyridine ruthenium/acid. Investigations were carried out by means of an electrochemical probe, at five temperatures between 5 and 45 °C. Activation energies (Ea) were estimated in different ways for the pre-oscillatory and oscillatory regimes. In any case, the Ea was found to depend on the catalyst, composition and initial concentrations. In addition, it was observed that ferroin and trisbipyridine ruthenium act as catalysts only during the transition between the induction period and oscillatory regime.

Análise de agrotóxicos em água usando extração líquido-líquido com partição em baixa temperatura por cromatografia líquida de alta eficiência

This study optimized and validated the liquid-liquid extraction technique with partition at low temperature (LLE-PLT) for identification and quantification of four pesticides (chlorpyrifos, λ-cyhalothrin, permethrin, bifenthrin) in water samples. Analyses were performed by HPLC-UV. The technique was efficient for pesticide recovery with extraction exceeding 86%. Chromatographic response was linear for the four compounds in the 10-45 µg L-1 range, with correlation coefficients greater than 0.99. Limits of detection and quantitation were less than 3.5 µg L-1 and equal to 10 µg L-1, respectively. The proposed method was applied to 29 water samples from the Jaíba Project in northern Minas Gerais.

Determinação de parâmetros cinéticos em fluxo com câmara de gradiente e deteção espectrofotométrica: aplicação à reação entre o violeta de cristal e o ião hidróxido

A didactic experiment is proposed aimed to extend the Flow Injection Analysis (FIA) based methodology to the area of physical chemistry/chemical reactors for undergraduate labs. Our prime objective was to describe the use of a gradient chamber for determination of the rate constant for the reaction between crystal violet and the hydroxide ion. The study was complemented by determining the effect of temperature on the rate constant. The kinetic parameters, activation energy and reaction rate constant are determined based on an assumption of rate orders. The main didactic advantages of the proposed experimental set-up are the use of less reagents, contributing to a more environmental friendly experiment. The experiment illustrates also the reduction of associated errors and time by using automated analysis owing to decreased operator manipulation.

Registrador portátil de odorantes basado en la modulación de temperatura de un sensor mos comercial

A simple, portable and low-cost system for odor detection was developed using a single MOS commercial sensor and a microcontroller. The temperature modulation technique was implemented applying a DC signal pulse to the sensor heater by a bipolar transistor. Two odorant profiles, ethanol and acetic acid vapors, were obtained and distinguished based on their amplitude versus time responses. Response for acetic acid was not reported by the sensor manufacturer. An ethanol vapor calibration curve was also obtained. Experimental data showed a potential behavior according to the theoretical equation of the MOS sensors. Values of logK=0.457 and α=-0.213 for a 95% confidence level were obtained.

Desenvolvimento do método de extração sólido-líquido com partição em baixa temperatura para determinação de inseticidas em grãos de milho ozonizados

The objective of this study was to optimize and validate a solid-liquid extraction method with low-temperature partitioning (SLE/LTP) for the analysis of pesticides. This method was coupled with gas chromatography (GC/ECD) and used to evaluate the degradation of bifenthrin and pirimiphos-methyl in maize grains on exposure to ozone. The optimized SLE/LTP-GC/ECD method is simple, effective and consumes low quantities of the solvent. It can be routinely used for the determination of bifenthrin and pirimiphos-methyl in maize samples. The use of this method of analysis determined that the levels of the insecticides in maize grains were reduced on exposure of the grains to the ozone gas. The observed reduction in the levels of insecticide was directly proportional to the increase in the concentration of the ozone gas.

Otimização e validação da extração sólido-líquido e purificação em baixa temperatura de HPAs em lodo de esgoto

In this study, a method of solid-liquid extraction and purification at low temperature (SLE-PLT) to determine 16 polycyclic aromatic hydrocarbons (PAHs) in sewage sludge was optimized and validated. The analyses were performed by HPLC-UV. The extraction phase, homogenization procedure, influence of pH, ionic strength and clean-up of the extracts were optimized. Recoveries were higher than 63.4% for 11 PAHs. The correlation coefficients were greater than 0.99 and limits of detection and quantitation were less than 0.060 and 0.15 µg g-1, respectively. These values were lower than the maximum residue limits of PAHs established by European legislation. SLE-PLT proved a more practical, economical method with fewer steps compared to Soxhlet extraction (reference method) for PAHs in sewage sludge.