Desenvolvimento de metodologia analítica para determinação de colesterol em ração para ruminantes através de planejamento experimental fatorial

A chromatographic method was developed for cholesterol determination in feed for ruminants using response surface methodology. Among the five approaches of sample preparation methods tested, the saponification of the sample without heating presented less interference in the gas chromatography. The method presented a relative standard deviation (RSD) of 4.3%, recoveries between 84 and 87% and detection limit of 0.001 mg of cholesterol per g of feed.

Principais aplicações das microondas na produção e refino de petróleo

Microwave irradiation offers a clean, inexpensive, and convenient method of heating, which is an alternative way of introducing energy into chemical systems. In particular, applications of microwave irradiation technology for petroleum processing have been developed in the last twenty years. The main objective of this paper is to review the use of microwave irradiation technology as an alternative technique applied during petroleum refining and primary processing of petroleum fluids, presenting and discussing successful applications of this technology as a tool for petroleum emulsion separation and catalytic reactions normally found at hydrorefining plants.

Síntese, caracterização e análise térmica dos sais de lítio, sódio e potássio do ácido palmítico e do seu éster etílico

Alkaline salts of the palmitic acid were synthesized and characterized from aqueous and ethanolic medium. The salts were characterized by elemental analysis (EA) and infrared spectroscopy (IR). EA and IR, being its synthesis comproved, also characterized the ethyl palmitate. All the salts and the ester were submitted to thermal analysis using thermogravimetry (TG), and differential thermal analysis (DTA) in the temperature ranging from room to 700 ºC under air dynamic atmosphere. Differential scanning calorimetry (DSC) measurements were taken from -90 ºC up to temperatures close to the starting of the decomposition temperature, determined by thermogravimetry, using heating and cooling cycles.

Construção de câmara de luz ultravioleta para fotopolimerização de fases estacionárias monolíticas

The assembly of a photochemical reactor with six fluorescent lamps, used for photopolymerizations is described. This chamber presents a mobile support, allowing the placement of samples at different heights and a safety lock that interrupts the radiation, if it is opened during operation. The mirrored internal walls avoid the dispersion and non-uniform distribution of light. There is no high heating because the own character of the used lamps. All parts could be purchased in commerce with less than U$ 150,00. This reactor was successfully used for monolithic stationary phase photopolymerization.

Biomassa e energia

Biomass was the dominating source of energy for human activities until the middle 19th century, when coal, oil, gas and other energy sources became increasingly important but it still represents ca. 10% of the worldwide energy supply. The major part of biomass for energy is still "traditional biomass" used as wood and coal extracted from native forests and thus non-sustainable, used with low efficiency for cooking and home heating, causing pollution problems. This use is largely done in rural areas and it is usually not supported by trading activities. There is now a strong trend to the modernization of biomass use, especially making alcohol from sugar cane thus replacing gasoline, or biodiesel to replace Diesel oil, beyond the production of electricity and vegetable coal using wood from planted forests. As recently as in 2004, sustainable "modern biomass" represented 2% of worldwide energy consumption. This article discusses the perspectives of the "first" and "second" technology generations for liquid fuel production, as well as biomass gaseification to make electricity or syngas that is in turn used in the Fischer-Tropsch process.

Estudo comparativo de métodos de preparo de amostras de tinta para a determinação de metais e metalóides por técnicas de espectrometria atômica

This work deals with paint decomposition methods for major, minor and trace elements determination. Three methods were investigated: (1) decomposition in closed quartz vessel and heating in microwave oven; (2) decomposition in open vessel using HNO3 and ashing, following the ASTM D 3335-85a method; and (3) decomposition in open vessel using HNO3 + HF and ashing. Paints of different types and colours were analyzed, in which several elements were determined using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP OES). It was observed that method (1) is appropriate for trace, minor and major elements determination, while method (3) is appropriate for Ti.

Development and application of spectrophotometric method for the determination of cefaclor in pharmaceutical formulations

A simple, fast and sensitive spectrophotometric method for the determination of cefaclor in pharmaceutical raw and dosage forms based on reaction with ninhydrin is developed, optimized and validated. The purple color (Ruhemenn's purple) that resulted from the reaction was stabilized and measured at 560 nm. Beer's law is obeyed in the concentration range of 4-80 µg mL-1 with molar absorptivity of 1.42 × 10(5) L mole-1 cm-1. All variables including the reagent concentration, heating time, reaction temperature, color stability period, and cefaclor/ninhydrin ratio were studied in order to optimize the reaction conditions. No interference was observed from common pharmaceutical adjuvant. The developed method is easy to use, accurate and highly cost-effective for routine studies relative to HPLC and other techniques.

Caracterização da fusão peritética do cloreto de sódio di-hidratado por curvas de aquecimento

Binary mixture phase diagrams are normally obtained from thermal analysis involving freezing point curves. However, that approach is not always reliable and easy to follow to all kinds of mixtures in any proportion. In fact, even for a simple system, such as NaCl-H2O, this freezing methodology gives mixed results when one starts from a solid-solution system, due mostly to the formation of the NaCl.2H2O, which has an incongruent melting point, and the dependence of its solubility with the temperature. In this work we report a trustworthy, simple and cheap method involving heating curves to drawn the NaCl-H2O phase diagram.

Determinação espectrofotométrica de hexametilenotetramina (HMT) em medicamentos, utilizando ácido cromotrópico e forno de micro-ondas

This paper proposes a methodology for spectrophotometric determination of hexamethylenetetramine (HMT) by using chromotropic acid in a phosphoric acid media employing a domestic microwave oven as a source of heating. The reddish-purple soluble product is quantitatively formed after 30 s of irradiation and obeys the Beer´s law in the range between 0.1-1.2 mg L-1 HMT (r = 0.99925). The method was applied successfully in commercial pharmaceutical preparations containing dyes in their composition. The results showed that the method proposed is feasible for simplicity, speed, low cost, precision and accuracy when compared with United States Pharmacopeia official method.

Câmaras climáticas para o envelhecimento acelerado: ação de microambientes sobre bens culturais

Environmental chambers were designed for the accelerated ageing of materials used in artistic artifacts to study the synergistic action of temperature, humidity, UV and visible radiation and gaseous pollutants. Two inox-steel/PTFE compartments are kept under controlled temperature and relative humidity, whose values are transmitted to a PC, which stores, plots in real time and continuously feedback heating and humidifying devices through logical signals. A borosilicate, or quartz, window allows the irradiation inside the chamber from an external source. A flow of purified air purges the chamber and conveys selected pollutants from an external source. Each independent compartment works under either stationary or cyclic conditions.

Salinidade em petróleo bruto: otimização de metodologia e proposta de um novo método para extração de sais em petróleo

The quantity of salts in the crude oils depends on the origin and of the wells production and these salts cause several problems during the transport and the process of refine as corrosions, incrustations and deactivation of the employed catalysts in the refineries. In this study were implemented changes for improvements in the execution of ASTM D 6470 method and has also developed a new methodology of extraction system of salts using process of mechanical agitation without heating. The results of the optimization produce larger efficiency and safety to the process compared to the traditional ASTM method.

Crescimento de cristais de rubi e safira pelo método do fluxo

This work reports the growth of corundum crystals by the flux method. The main objective was the evaluation of versatility, effectiveness and real possibilities of the flux method to the synthesis and doping of monocrystals with impurities of particular interest. In this work the chosen impurities were i) Cr and ii) Fe and Ti, aiming the synthesis of rubies and sapphires, respectively. The crystals were grown by heating a mixture of Al2O3:Cr or Al2O3:Fe:Ti and flux (MoO3). The maximum crystal size obtained was 1.0 mm, all transparent, presenting well developed faces, bipiramidal hexagonal shape, and showing a typical red (ruby) and/or light blue (sapphire) color. EDX and XPD experiments were performed in order to characterize some of the synthesized crystals. All crystallized specimens presented the α-alumina atomic structure.

Influência da quantidade de amônio na síntese de nanopartículas de óxido de ferro por microemulsão

Iron oxide nanoparticles were synthesized in microemulsion systems composed by Triton X-100/hexyl alcohol/cyclohexane/aqueous solution. The nanoparticles were synthesized in microemulsions containing different amounts of ammonium, in order to evaluate the influence of this parameter on the size of the nanoparticles and on the phase transformation after heat treatment. Powder materials were obtained after centrifugation, washing and drying, and they were analyzed as synthesized and after heating at 350, 500 and 1000 °C. It was observed that the higher amount of ammonium induced smaller particles and minor phase transformation, possibly due to a preferential nucleation process.

Determinación de los parámetros cinéticos en la pirólisis del pino ciprés

The study of pyrolysis is gaining increasing importance, since it is the first step in the gasification or combustion process. In this study, pyrolysis experiments of cypress pine were carried out in a thermogravimetric analyzer at six different heating rates between 5 and 40 ºC / min. Kinetics parameters of pine were determined from TGA by using the differential and the maximum speed methods. Additionally, the distribution of activation energies was also carried out finding the values of 113.57 and 157.32 kJ/mol, which are in the range of activation energies reported for hemicellulose and cellulose, respectively, main components of wood.

O uso de aparelhos de micro-ondas domésticos em aulas experimentais de química orgânica: nitração de salicilaldeído

The use of microwave in chemistry has known benefits over conventional heating methods, e.g. reduced reaction times, chemical yield improvement and the possibility if reducing or eliminating the use of organic solvents. We describe herein a procedure for the nitration of salicylaldehyde in water using a domestic microwave oven, which can be used as an experiment in the undergraduate chemistry laboratory. The experiment involves safe and rapid preparation and identification of the position isomers by thin layer chromatography and 1H NMR, or by their melting points.