Construção de célula eletroquímica para observação de amostras in situ em estereomicroscópio

The electrochemical study of glass like tungsten oxide derivatives requires the construction of special electrodes due to the fact that these glasses are not conductive. Electrodes modified with WO3 change their color when submitted to some potential perturbation. The color change of the electrochromic materials was observed in situ by coupling an electrochemical cell to a stereomicroscope. The constructed cell is versatile and may represent a great contribution to the electrochemical studies of materials, especially in the systems where it is interest to observe the working electrode surface during the electrochemical experiment.

Produção de biodiesel através de transesterificação in situ de sementes de girassol via catálise homogênea e heterogênea

The objective of this work is to show the results of the in situ transesterification of sunflower seed oil with methanol on basic homogeneous and heterogeneous catalysis for the production of biodiesel. In homogeneous catalysis, the activity of KOH and K2CO3 were evaluated using the same oil:methanol ratio of 1:90. KOH showed to be more active than K2CO3, leading to total conversion in biodiesel after 1h reaction time. In the heterogeneous catalysis the activity of K2CO3/Al2O3 was comparable to the activity of K2CO3 bulk: 53.0 and 66.6% resp. The properties of samples of biodiesel produced by homogeneous and heterogeneous catalysis were evaluated and are in accordance with the recommended fuel properties.

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.

In situ synthesis of nanoclay filled polyethylene using polymer supported metallocene catalyst system

In situ ethylene polymerizations were performed using bis(cyclopentadiene)titanium dichloride supported on polyethersulfone as catalyst. The bis(cyclopentadiene)titanium dichloride supported on polyethersulfone catalyst activity estimated by ethylene polymerization was 360 kgPE/molTi/h. During polymerization the fillers used were montmorillionite nanoclays having surface modifications with 35-45 wt% dimethyl dialkyl(14-18)amine (FA) and 25-30 wt% trimethyl stearyl ammonium (FB). These fillers were pretreated with methylaluminoxine (MAO; cocatalyst) for better dispersion onto the polymer matrix. The formation of polyethylene within the whole matrix was confirmed by FTIR studies. It was found that the nature of nanofiller did not have any remarkable effect on the melting characteristics of the polymer. TGA study indicates that nanoclay FB filled polyethylene has higher thermal stability than nanoclay FA filled polyethylene. The melting temperature of the obtained polyethylenes was 142 ºC, which corresponds to that synthesized by the polyether sulfone supported catalyst.

Construção de uma câmara para monitoramento in situ do processo de secagem de geis e sólidos porosos

The present work deals with the design and construction of an equipment for studying the drying process of gels and solids. The equipment was built using mainly a commercial oven and others peripherals for programmed control of temperature, humidity and data acquisition. The system allows the in situ monitoring of the gel drying, registering the weight loss, and the shrinkage of sample and the oven temperatures. This set of allowed parameters makes possible to establish the main steps involved in the drying of meso and nanostructured porous materials.

Construction and application of a portable microcontrolled turbidimeter for the in situ determination of sulfate

This study reports on the construction of a turbidimeter employing light emitting diodes as radiation source at a wavelength of 405 nm, a photodiode as detector, a temperature sensor and a microcontroller used for data acquisition and processing. The turbidimeter was applied to determine sulfate concentrations in natural water employing barium chloride as reagent. Potential interferences and recovery studies were performed and an interference of 3.5 % and a recovery between 97.8 and 108 % were estimated. The analytical performance of in situ turbidimeter for the determination of sulfate was evaluated and compared with two commercial spectrophotometers and a good agreement was obtained.

Desenvolvimento e avaliação de eletrodos de difusão gasosa (EDG) para geração de H2O2 in situ e sua aplicação na degradação do corante reativo azul 19

This work reports the development of GDE for electrogeneration of H2O2 and their application in the degradation process of Reactive Blue 19 dye. GDE produced by carbon black with 20% polytetrafluoroethylene generated up to 500 mg L-1 of H2O2 through the electrolysis of acidic medium at -0.8 V vs Ag/AgCl. Reactive Blue 19 dye was degraded most efficiently with H2O2 electrogenerated in the presence of Fe(II) ions, leading to removal of 95% of the original color and 39% of TOC at -0.8 V vs Ag/AgCl.

Development of a simple analytical method for determining trihalomethanes in beer using a headspace solid-phase microextraction technique

We developed a simple, rapid, and solventless method for analyzing trihalomethanes in beer samples using headspace solid-phase microextraction. The effects of varying experimental parameters, such as extraction temperature and time, addition of sodium chloride, and agitation speed, on extraction yield were studied using a univariate experimental design. Limits of detection between 0.22 and 0.46 µg L- 1 and wide linear ranges were achieved for trihalomethanes. We measured the trihalomethane recoveries and precision (as the standard deviation of repeat measurements) and demonstrated the applicability of the proposed method by analyzing 32 beer samples.

Optimization of solvent mixtures for extraction from bark of Schinus terebinthifolius by a statistical mixture-design technique and development of a UV-Vis spectrophotometric method for analysis of total polyphenols in the extract

A statistical mixture-design technique was used to study the effects of different solvents and their mixtures on the yield, total polyphenol content, and antioxidant capacity of the crude extracts from the bark of Schinus terebinthifolius Raddi (Anacardiaceae). The experimental results and their response-surface models showed that ternary mixtures with equal portions of all the three solvents (water, ethanol and acetone) were better than the binary mixtures in generating crude extracts with the highest yield (22.04 ± 0.48%), total polyphenol content (29.39 ± 0.39%), and antioxidant capacity (6.38 ± 0.21). An analytical method was developed and validated for the determination of total polyphenols in the extracts. Optimal conditions for the various parameters in this analytical method, namely, the time for the chromophoric reaction to stabilize, wavelength of the absorption maxima to be monitored, the reference standard and the concentration of sodium carbonate were determined to be 5 min, 780 nm, pyrogallol, and 14.06% w v-1, respectively. UV-Vis spectrophotometric monitoring of the reaction under these conditions proved the method to be linear, specific, precise, accurate, reproducible, robust, and easy to perform.

Preconcentration of copper from natural water samples using ligand-less in situ surfactant-based solid phase extraction prior to FAAS determination

In the present work, a simple and rapid ligand-less, in situ, surfactant-based solid phase extraction for the preconcentration of copper in water samples was developed. In this method, a cationic surfactant (n-dodecyltrimethylammonium bromide) was dissolved in an aqueous sample followed by the addition of an appropriate ion-pairing agent (ClO4-). Due to the interaction between the surfactant and ion-pairing agent, solid particles were formed and subsequently used for the adsorption of Cu(OH)2 and CuI. After centrifugation, the sediment was dissolved in 1.0 mL of 1 mol L-1 HNO3 in ethanol and aspirated directly into the flame atomic absorption spectrometer. In order to obtain the optimum conditions, several parameters affecting the performance of the LL-ISS-SPE, including the volumes of DTAB, KClO4, and KI, pH, and potentially interfering ions, were optimized. It was found that KI and phosphate buffer solution (pH = 9) could extract more than 95% of copper ions. The amount of copper ions in the water samples varied from 3.2 to 4.8 ng mL-1, with relative standard deviations of 98.5%-103%. The determination of copper in water samples was linear over a concentration range of 0.5-200.0 ng mL-1. The limit of detection (3Sb/m) was 0.1 ng mL-1 with an enrichment factor of 38.7. The accuracy of the developed method was verified by the determination of copper in two certified reference materials, producing satisfactory results.

Detection of Rhynchosporium secalis in barley seeds from Argentina through polymerase chain reaction technique

Leaf scald of barley caused by Rhynchosporium secalis is an important disease in Argentina. The fungus is a necrotrophic pathogen which survives in stubble, seeds and weeds. Isolation of R. secalis from seeds on artificial media usually has not been successful due to the slow growth rate of the pathogen and strong inhibition by contaminants. The objective in this work was to detect R. secalis in different genotypes of barley seeds in Argentina using the polymerase chain reaction (PCR)-based diagnostic assay. Four barley genotypes were tested in 2004: Quilmes Ayelén, Quilmes Alfa, Barke and Maltería Pampa 1004. The previously described RS8 and RS9 primers were used for the detection of R. secalis in barley seeds. A 264-bp single band was obtained for each cultivar showing the presence of R. secalis. The use of specific primers was efficient in the detection of R. secalis in barley seeds in Argentina and could be used for routine diagnosis, epidemiology and seed transmission studies. This is the first report on the detection of R. secalis in barley seeds in Argentina.

Hemiselluloosien erotus ja in situ -modifiointi

Hemiselluloosat kuuluvat selluloosan ja ligniinin ohella puun ja muiden kasvimateriaalien päärakenneaineksiin. Hemiselluloosan kemiallisessa koostumuksessa on eroja kasvilajien välillä, mikä tekee ryhmästä hyvin monimuotoisen. Lehtipuiden pääasiallinen hemiselluloosa on glukuroniksylaani. Ksylaaneja esiintyy laajasti myös muissa kasveissa erilaisina rakenteina. Havupuiden yleisin hemiselluloosa on puolestaan galaktoglukomannaani. Arabinogalaktaani on erityisesti lehtikuusesta runsaana löytyvä hemiselluloosa, jota muissa puulajeissa on vain vähän. Luonnon polymeerejä tutkitaan jatkuvasti muun muassa vaihtoehtojen löytämiseksi raakaöljypohjaisille tuotteille. Aiemmin hemiselluloosia on pääosin hyödynnetty sellaisenaan tai jalostettu esimerkiksi sokereiksi. Selluloosan ja tärkkelyksen tavoin ne voivat kuitenkin toimia myös kemiallisen, fysikaalisen tai entsymaattisen muokkauksen lähtöaineena. Hemiselluloosien käyttöä rajoittaa usein se, että niiden eristäminen kasvimateriaalista hyvällä saannolla on vaikeaa. Useimmiten hemiselluloosa erotetaan biomassasta ligniinin poiston jälkeen uuttamalla erilaisilla reagensseilla, kuten emäksillä. Arabinogalaktaanin erottamiseen ei kuitenkaan vaadita ankaria olosuhteita, vaan yleisimmin siihen riittää uutto vedellä. Kalvosuodatus puolestaan on hyvä keino hemiselluloosan talteenottoon uuttoliuoksista. Tässä työssä tarkasteltiin arabinogalaktaanin erotusta siperianlehtikuusesta uuttokokein. Saadut uuttoliuokset konsentrointiin ja puhdistettiin kalvosuodatusmenetelmillä. Lisäksi tutkittiin eristetyn arabinogalaktaanin käyttöä kemiallisen muokkauksen lähtöaineena, missä pyrkimyksenä oli etenkin in situ -modifiointi suoraan uuttoliuoksessa oleville yhdisteille. Uuttokokeilla saatiin kuitenkin vain pieni osa lehtikuusen arabinogalaktaanista erotetuksi. Myös kalvosuodatusvaiheen aikana menetettiin osa uuttoliuosten arabinogalaktaanista. Koska arabinogalaktaanipitoisuus uuttoliuoksissa jäi hyvin alhaiseksi, in situ -modifiointeja oli vaikea saada onnistumaan. Uutto-olosuhteiden lisätutkimuksella sekä kiinnittämällä erityistä huomiota suodatuskalvojen valintaan voitaneen pitoisuutta nostaa ja saada lisämateriaalia kemiallista muokkausta varten.

Exploring potentialities of the HR-CS FAAS technique in the determination of Ni and Pb in mineral waters

National Health Surveillance Agency (ANVISA) established in the decree number 54 maximum allowed levels for Ni and Pb in mineral and natural waters at 20 µg L-1 and 10 µg L-1, respectively. For screening analysis purposes, the high-resolution continuum source flame atomic absorption spectrometry technique (HR-CS FAAS) was evaluated for the fast-sequential determination of nickel and lead in mineral waters.Two atomic lines for Ni (232.003 nm - main and 341.477 nm - secondary) and Pb (217.0005 nm - main and 283.306 nm - secondary) at different wavelength integrated absorbance (number of pixels) were evaluated. Sensitivity enhanced with the increase of the number of pixels and with the summation of the atomic lines absorbances. The main figures of merit associated to the HR-CS FAAS technique were compared with that obtained by line-source flame atomic absorption spectrometry (LS FAAS). Water samples were pre-concentrated about 5-fold by evaporation before analysis. Recoveries of Pb significantly varied with increased wavelength integrated absorbance. Better recoveries (92-93%) were observed for higher number of pixels at the main line or summating the atomic lines (90-92%). This influence was irrelevant for Ni, and recoveries in the 92-104% range were obtained in all situations.