Aplicação de extratos brutos de flores de quaresmeira e azaléia e da casca de feijão preto em volumetria ácido-base. Um experimento para cursos de análise quantitativa

Crude extract of Tibouchina granulosa, Rhododendron simsii and Phaseolus vulgaris L. were prepared and used as alternative indicators in quantitative analysis teaching in standardization of NaOH solutions and in the determination of acetic acid contents in vinegar. Effect of using such natural extracts as indicators was very attractive to the students and the quantitative results were compared with conventional indicators with good agreement. Concepts of data statistics can successfully be discussed using the interest revived by the use of natural indicators.

Análise conformacional de modelos de lignina

The conformational equilibrium for two 5,5' biphenyl lignin models have been analyzed using a quantum mechanical semiempirical method. The gas phase and solution structures are discussed based on the NMR and X-ray experimental data. The results obtained showed that the observed conformations are solvent-dependent, being the geometries and the thermodynamic properties correlated with the experimental information. This study shows how a systematic theoretical conformational analysis can help to understand chemical processes at a molecular level.

Métodos matemáticos para correção de interferências espectrais e efeitos interelementos na análise quantitativa por fluorescência de raios-X

One of the main problems in quantitative analysis of complex samples by x-ray fluorescence is related to interelemental (or matrix) effects. These effects appear as a result of interactions among sample elements, affecting the x-ray emission intensity in a non-linear manner. Basically, two main effects occur; intensity absorption and enhancement. The combination of these effects can lead to serious problems. Many studies have been carried out proposing mathematical methods to correct for these effects. Basic concepts and the main correction methods are discussed here.

Injetor multicanal com válvulas de estrangulamento para análise em fluxo

An important component for the automation of flow injection analysis (FIA) systems is the sample injection valve. A simple and inexpensive commutator with 16 pinch valves (8 normally open and 8 closed) was developed and configured as a multichannel injection valve. It is activated by a single solenoid of 3 Kgf, powered by a pulsed driver circuit, controlled by a microcomputer or a switch. FIA with spectrophometric detection of potassium dichromate solution was used for the evaluation of the new injection valve and its comparison with other valves, for sample loops of 50, 100, 200, 300 and 500 muL. The repeatability was favorable (RSD 1.0% for 15 injections at each loop volume) compared to a manual injector, an electropneumatic injector and an injector configured with three mini solenoid valves (RSD 1.1, 1.3 and 1.0%, respectively, for15 injections at each loop volume).

Propulsor pneumático versátil e isento de pulsação para sistemas de análise em fluxo

Aquarium air pumps are proposed and evaluated as pneumatic liquid propulsion devices for flow injection and continuos flow analysis (FIA and CFA) systems. This kind of pump is widely available at a very low cost and it can sustain a pressure around of 4 psi (0.28 bar) indefinitely. By applying this air pressure onto a solution contained in a reservoir flask, it is possible to reach flow rates of up to 12.5 mL min-1 for circuits comprising reactors, made from 0.8 i.d. tubing with a length of 100 cm. The precise adjustment of flow rate below the maximum one can be made with a simplified needle valve or inserting in series a short length of capillary tube. The absence of flow pulsation is a definite advantage in comparison with peristaltic pumps, especially when amperometric detection is elected, as confirmed experimentally in FIA and CF applications.

CGAR E CGAR-EM na análise dos constituintes químicos isolados do extrato hexanico de Sebastiania argutidens (Euphorbiaceae)

The fractionation column with SiO2 of the hexane extract of Sebastiania argutidens (Euphorbiaceae) yielded fractions containing hydrocarbons, carboxylic acids, sterols and pentacyclic triterpenes. Besides, one fraction showed the presence of several methyl esters, including four uncommon long chain palmitate esthers as minor components. The characterization of these chemical constituents have been done by High Resolution Gas Chromatography (HRGC) and HRGC coupled to Mass Spectrometry (GC/MS). Campesterol, stigmasterol, b-sitosterol, glutin-5-en-3-ol were identified by HRGC co-injection with standards.

Aspectos práticos relacionados ao uso do Rincoforol, o feromônio de agregação da Broca-do-olho-do-coqueiro Rhynchophorus palmarum L. (Coleopterate: Curculionidae) no controle de pragas do coqueiro: análise de sua eficiência em campo

Rhynchophorol (6-Methyl-2-hepten-4-ol) is the major constituent of the aggregation pheromone of Rhynchophorus palmarum L. (Coleoptera: Curculionidae), which is released by males of this species. The racemic mixture has been produced in one step-simplified preparation. The pheromone is placed into ampoules and furnished to coconut farmers. In the field, traps baited with Rhynchophorol and pieces of sugarcane attract both males and females, reducing the population of R. palmarum. The best conditions for field application are showed.

Técnicas para análise de desempenho de computadores

A series of open source benchmarks for computer performance analysis of personal computers with a focus on computational chemistry calculations is presented. The results returned by these tests are discussed and used to correlate with the actual performance of a set of computers available for research on two computing intensive fields of chemistry, quantum chemical and molecular simulation calculations.

Análise de resíduos de pesticidas em tomates por cromatografia em camada delgada

Pesticide residues are determined by thin layer chromatography (TLC) using the Hill reaction as a detection method. Tomatoes samples without pesticide were fortified with atrazine, diuron, chloroxuron and metribuzin, and were applyed in silica gel plates with the help of a microsyringe. The pesticides were elued with ethyl acetate. There was no need of cleaning up because no interference was noticed. After the revelation of the plates, the diameters of the spots were measure by using a rule. The range of the determined concentration for all the pesticides was from 0.1 to1.0 ng/muL. The results obtained through TLC can be used for semi-quantitative analysis.The results obtained were compared to gas and liquid chromatography, showing good agreement between both techniques.

Estudo do efeito do cloreto em catalisadores de paládio usando a análise no infravermelho e de fotoelétrons excitados por raios x

Chloride poisoning is known as having an inhibitor effect in the activity of metal catalysis. In this work in situ infrared spectroscopy (FTIR) of adsorbed carbon monoxide and x-ray photoelectron spectroscopy (XPS) were used to investigate the effect of chloride presence in the electronic metal density in the d subshell of palladium dispersed on alumina. The chloride poisoning effect was interpreted as an electronic effect since a weak back-bonded Pd-CO was formed due to the decrease in the electronic density of the d subshell of palladium, which could be also detected by the higher Pd 3d5/2 binding energy in the chloride presence. A similar poisoning effect was also observed for chloride free Pd/Al2O3 reduced at 500 ºC, and it was interpreted based on the interaction of metal with the alumina surface. The use of molybdena/alumina binary system as support, yield a contrary effect due to the metal-support interaction.

Sistemas interfaceados de análise por injeção em fluxo e eletroforese capilar (FIA - CE): desafios, aplicações e perspectivas

A review about the state-of-the-art of flow injection analysis (FIA) -- capillary electrophoresis (CE) systems is presented. The basic principles of flow injection and capillary electrophoresis are briefly revised. The main aspects of the FIA-CE hybridization, including advantages and shortcomings, are discussed. Some applications involving all different designs are also presented. This review covers the literature from 1997 up to 2000.

A quimiluminescência como ferramenta analítica: do mecanismo a aplicações da reação do luminol em métodos cinéticos de análise

Relevant aspects of proposed mechanisms of the chemiluminescent reaction of luminol are presented and commented to emphasize its perspectives for kinetic analysis. A careful search for analytical applications of this reaction is discussed in order to point out new trends of the studies. Kinetic analysis using the luminol reaction is proposed to be a very attractive due to the good performance of the reaction in analytical applications and the positive characteristics of kinetic analysis, such as low cost and sensibility. It is pointed out that kinetic analysis using the chemiluminescent reaction of luminol should be encouraged.

Estudo QSPR sobre os coeficientes de partição: descritores mecânico-quânticos e análise multivariada

Quantum chemistry and multivariate analysis were used to estimate the partition coefficients between n-octanol and water for a serie of 188 compounds, with the values of the q 2 until 0.86 for crossvalidation test. The quantum-mechanical descriptors are obtained with ab initio calculation, using the solvation effects of the Polarizable Continuum Method. Two different Hartree-Fock bases were used, and two different ways for simulating solvent cavity formation. The results for each of the cases were analised, and each methodology proposed is indicated for particular case.

Análise de glicocorticosteróides por CG-EM: uma nova abordagem de derivatização para o controle de dopagem no esporte

Glucocorticosteroids (CT) show a powerful anti-inflammatory effect. In view of this, they are extensively used in sports medicine, but their misuse (systemic administration) can lead to severe injuries on athletes and has been restricted by the IOC in recent years. For GC-MS analysis, a derivatization step is necessary in order to convert them to a stable form, thus preventing thermal breakdown with the loss of the ketone side chain. Derivatization of CT is reviewed and a new approach of silylation is presented for screening of CT in urine.

Análise de suspensões de argilas por espectrometria de emissão óptica com plasma induzido com configuração axial

The goal of this study was to evaluate the feasibility of direct introduction of clay slurries in an inductively coupled plasma optical emission spectrometer with axial view configuration. Calibration was performed using a certified reference material with a mean particle size of 13 µm (IPT-42) and the analytical curve was applied for quantification of two others reference materials (IPT-28 and IPT-32) and four samples. It was demonstrated that the analytical curve thus obtained was not completely suitable for IPT-28 and samples due to different mineralogical phases determined by X-ray diffraction. After considering this effect, it was possible for most elements to obtain results in agreement with certified values or with values obtained by a conventional technique at a 95% confidence level. It was demonstrated that the ICP-OES with axial view configuration did not present any incompatibility with the direct introduction of a complex inorganic suspension.