Carbono do solo e a mitigação da mudança climática global

The soils of the world contain more carbon than the combined total amounts occurring in vegetation and the atmosphere. Hence soils are a major reservoir of carbon in terrestrial ecosystems and an important sink. Recently, emphasis has been placed on the need to sequester carbon from atmospheric carbon dioxide into soil organic matter because of international concerns about greenhouse gas emissions and global climate change. The best strategies to built-up carbon stocks in the soil are basically those that increase the input of organic matter to the soil, and/or decrease the rate of soil organic matter decomposition. Grain crop systems based on soil ploughing and harrowing lead to CO2 emissions combined with tremendous soil losses. In Brazil, no-tillage system was introduced to combat soil erosion by water and this soil management led to the build-up of soil carbon stocks with simultaneous high crop yields. However, the present procedure used to quantify carbon stocks in soils is laborious and of high cost. The use of infrared spectroscopy is very promising as an alternative low-cost method of soil carbon determination.

Construção e avaliação de célula de fluxo para estudo da tensão interfacial dinâmica da interface fluxo líquido - sólido por despolarização da fluorescência

A simple low-cost flow cell was developed, built and optimized in order to observe dynamic interfacial tension of continuous flow systems. Distinct materials can be used in one of the cell walls in order to observe the intermolecular forces between the flowing liquid and the chemical constitution of the walls. The fluorescence depolarization was evaluated using Rhodamine B as fluorescent probe seeded in ethylene glycol. The effects of the positioning angles on the data acquired across the cell are reported. The reproducibility of the data was evaluated with a spectrometer assembled in-house and the relative standard deviation was below 3%.

Montagem de câmara com lâmpada de ultravioleta de baixo custo

Thin layer chromatography is a quick, inexpensive and effective way of screening mixtures of non-volatile organic compounds and it is highly recommended for analytical studies. Inspection of plates under ultraviolet light for the detection of colourless compounds should be performed before any further chemical methods are applied. Construction of a low-cost UV-viewing cabinet with lamp employing parts easily found on the local market is described.

Uso de agrotóxicos em cana-de-açúcar na bacia do Rio Corumbataí e o risco de poluição hídrica

The state of São Paulo is the main Brazilian consumer of pesticides. Sugar cane, which uses a great amount of these products, is extensivelly cultivated in this state, such as in the Corumbataí river basin, an important source of water for the region. In order to implement an efficient and low-cost monitoring program, the temporal characterization of the use of pesticides on sugar cane in this basin was performed. After knowing the seasonal trends of consumption, a better choice of sampling time, became possible. The combination of data from this survey with partitioning indices, average doses and toxicological classifications showed to be important for defining the pesticides to be included in the monitoring program.

Stability-indicating methods for quantitative determination of zidovudine and stavudine in capsules

Zidovudine (AZT) and stavudine (D4T) are nucleoside reverse transcriptase inhibitors extensively used in human immunodeficiency virus (HIV) infected patients. In order to evaluate the quality of these drugs, two stability indicating HPLC methods were developed. The validated methods were applied in quantitative determination of AZT, D4T and their induced degradation products in capsule preparations. The stability studies were conducted at controlled temperature and relative humidity conditions based on the International Conference on Harmonization stability studies protocol for Zone IV areas. Easy sample preparation and low-cost make these methods especially useful for quality control and stability studies of AZT and D4T in drug products.

Extração de esterase de fígado suíno (PLE)

A simple, fast and low-cost methodology was optimized, seeking preparation of a crude pig liver esterase (PLE) concentrate. Basically, the method consisted of the following steps: liver homogenization, acetone washing, enzyme extraction and purification/concentration. Starting from 1 kg of fresh liver more than 200 kU of PLE suspension were obtained after 8 hours, at an estimated cost of US$0.21/kU. The PLE concentrate thus obtained was stable, showing 96-100% of the initial activity after 7 months in refrigerator at 4°C.

Um aparato para monitorar reações rápidas: um "stopped-flow" artesanal de baixo custo

The modern stopped-flow reaction analyzer has shown high efficiency and flexibility, which provides outstanding sample economy with a dead-time of less than 1 ms. However the cost of the equipment imposes a serious restriction to many Brazilian scientists and teachers. In this work we describe the construction of a low-cost stopped-flow system coupled to a UV-Vis spectrophotometer. The performance of the system was checked by monitoring the kinetics of two reactions: the fading of phenolphthalein in aqueous alkaline solution and the chlorophyll a demetallation in acid medium. The apparatus showed reasonable efficiency with a dead-time of 0.3 to 0.5 s. The very good results obtained in these two illustrative processes show that the system is satisfactory for determining rate constants with mean reaction times ranging from seconds to minutes.

Cafeína: revisão sobre métodos de análise

Gravimetric and Bailey-Andrew methods are tedious and provide inflated results. Spectrofotometry is adequate for caffeine analysis but is lengthy. Gas chromatography also is applied to the caffeine analysis but derivatization is needed. High performance liquid chromatography with ultraviolet detection (HPLC-UV) and reversed phase is simple and rapid for xanthine multianalysis. In HPLC-UV-gel permeation, organic solvents are not used. HPLC-mass spectrometry provides an unequivocal structural identification of xanthines. Capillary electrophoresis is fast and the solvent consumption is smaller than in HPLC. Chemometric methods offer an effective means for chemical data handling in multivariate analysis. Infrared spectroscopy alone or associated with chemometries could predict the caffeine content in a very accurate form. Electroanalytical methods are considered of low cost and easy application in caffeine analysis.

Photomultiplier nonlinear response in time-domain laser-induced luminescence spectroscopy

A new procedure to find the limiting range of the photomultiplier linear response of a low-cost, digital oscilloscope-based time-resolved laser-induced luminescence spectrometer (TRLS), is presented. A systematic investigation on the instrument response function with different signal input terminations, and the relationship between the luminescence intensity reaching the photomultiplier and the measured decay time are described. These investigations establish that setting the maximum intensity of the luminescence signal below 0.3V guarantees, for signal input terminations equal or higher than 99.7 ohm, a linear photomultiplier response.

Experimentação em química de compostos organometálicos: preparação do cloreto de dicarbonilciclopentadienilferro(II)

In this work, we describe a new method for obtaining [Fe(CO)2[(eta5-C5H5)Cl] employing simple techniques and low-cost reagents. It is worth mentioning that this method is faster than others reported in the literature. It was applied in laboratory classes for undergraduate students, exploring different concepts in organometallic chemistry and discussing the steps involved in the synthetic route.

Determinação de zinco em solo utilizando colorimetria

In terms of soil fertility, zinc is a micronutrient that is very important in the culture of soy, maize, rice and coffee, because it is a structural and functional component of a great number of enzymes. Therefore, diverse methods have been used to determine zinc in soil. In this work we use colorimetry as a methods of zinc determination in soil using two methodologies of sample digesting, H2SO4/H2O2 and HNO3/H2O2. In order to compare the results, atomic absorption spectrometry (AAS) was used. Results show that colorimetric methods can be used due to good sensitivity and reproducibility, since the zinc calibration curve showed good linearity. Comparing colorimetric methods with AAS we observed that the results were equivalent, as proven by the statistical values of the F and t of Student tests. Furthermore, both methods of soil digesting can be used, leading to a flexible methodology of low-cost for routine zinc analyses in soil.

Inativação fotodinâmica de microrganismos

Photodynamic Therapy uses photosensitive dyes and visible light that, combined in the presence of oxygen, produce cytotoxic species that cause tumor death. Microorganisms such as bacteria, fungi, yeasts and viruses (including HIV) can also be inactivated by visible light after treatment with an appropriate photosensitizer as an alternative low cost treatment for localized infections, viral lesions such as acnes, and fungical skin lesions for example. Besides, Photodynamic Inactivation can be used for sterilization of blood and its subproducts for clinical use, in the treatment of drinking water as well as in antimicrobial detoxification of foods.

Extraction, purification and biochemical characterization of a peroxidase from Copaifera langsdorffii leaves

The aim of this work is to obtain, purify and characterize biochemically a peroxidase from Copaifera langsdorffii leaves (COP). COP was obtained by acetone precipitation followed by ion-exchange chromatography. Purification yielded 3.5% of peroxidase with the purification factor of 46.86. The COP optimum pH is 6.0 and the temperature is 35 ºC. COP was stable in the pH range of 4.5 to 9.3 and at temperatures below 50.0 ºC. The apparent Michaelis-Menten constants (Km) for guaiacol and H2O2 were 0.04 mM and 0.39 mM respectively. Enzyme turnover was 0.075 s-1 for guaiacol and 0.28 s-1 for hydrogen peroxide. Copaifera langsdorffii leaves showed to be a rich source of active peroxidase (COP) during the whole year. COP could replace HRP, the most used peroxidase, in analytical determinations and treatment of industrial effluents at low cost.

Avaliação da composição química de águas do Sistema Guarapiranga: estudo de caso nos anos de 2002 e 2003

The supply of drinking water in the Metropolitan Area of São Paulo City has been a great and serious challenge in the latest years. This work demonstrates the viability of the evaluation of the degree of contamination of the water reservoirs using analytical procedures, which allow the analysis of several compounds at relatively low cost: stripping square wave voltammetry (SSWV) and capillary zone electrophoresis with contactless conductivity detection (CZE-CCD). The results of ionic composition indicated significant contamination of the Guarapiranga water system by human activities on the reservoir banks. In fact, the Guavirutuba and Itupu streams presented high concentrations of phosphate and ammonium ions. This can be directly related to misuse and unruled occupation of the soil and precarious sanitary infrastructure.

Desenvolvimento de método analítico por CLAE em comprimidos de Benznidazol para a Doença de Chagas

The analytical method of high performance liquid chromatography (HPLC) for the assay of benznidazole in tablets was developed and validated following the requirements of regulatory agencies. The method used as mobile phase acetonitrile:wather 1:1, a C18 column of 12.5 cm length x 4 mm id, 5 mm particles and lambda=316 nm. The statistical analysis of the results demonstrated that the method satisfies all parameters so as to be considered a safe and efficient analytical alternative of low cost for laboratory routine.