Digestão de óleo lubrificante encapsulado em forno de microondas com radiação focalizada por adição de amostra ao reagente pré-aquecido

The applicability of the recently proposed procedure based on gradual sample addition to microwave-assisted pre-heated concentrated acid is limited by the sample viscosity. In this work, lubricating oil samples with high viscosity were encapsulated and manually added to the microwave-assisted pre-heated concentrated digestion mixture. The procedure was applied for determination of Al, Ca, Cr, Cu, Fe, Mg, Ni, P, Pb, Si, Sn, Sr, V, W, and Zn in lubricating oil by inductively coupled plasma optical emission spectrometry (ICP OES). Determined and certified values for Ca, Mg, P, and Zn in lubricating oil were in agreement at a 95% confidence level.

Estudo da oxidação total do etanol usando óxidos tipo perovskita LaBO3 (B= Mn, Ni, Fe)

The present work investigated the effect of coprecipitation-oxidant synthesis on the specific surface area of perovskite-type oxides LaBO3 (B= Mn, Ni, Fe) for total oxidation of ethanol. The perovskite-type oxides were characterized by X-ray diffraction, nitrogen adsorption (BET method), thermogravimetric analysis (TGA-DTA), TPR and X-ray photoelectron spectroscopy (XPS). Through method involving the coprecipitation-oxidant was possible to obtain catalysts with different BET specific surface areas, of 33-51 m²/g. The results of the catalytic test confirmed that all oxides investigated in this work have specific catalytic activity for total oxidation of ethanol, though the temperatures for total conversion change for each transition metal.

Resistência mecânica de hidrogéis termo-sensíveis constituídos de Alginato-Ca2+ / PNIPAAm, tipo Semi-IPN

Thermosensitive hydrogels were synthesized using alginate-Ca2+ in association with a thermosensitive polymer, such as PNIPAAm. The mechanical properties of the hydrogels were determined measuring the maximum tension of deformation. With the increase of the temperature by 25 to 40 ºC above the LCST the chains of PNIPAAm collapsed, dragging the alginate net and diminishing the size of the pores. The decrease in the size of the pores of the hydrogel was followed by an increase in the mechanicals resistance of the material.

Diterpenos tipo abietano isolados de Plectranthus barbatus Andrews

Plectranthus barbatus is largely used in the Northeast region of Brazil by the local population for treatment of digestive problems as substitute of boldo (Pneumus boldus). Phytochemical analysis of the leaf extracts of Plectranthus barbatus (Labiatae) cultivated in this region yielded two abietane diterpenoids, cyclobubatusin (1) and barbatusin (2) and a new one named 7beta-acetyl-12-deacetoxycyclobutatusin (3). The structures of the isolated compounds were established by spectral analysis, using mainly mass spectra and ¹H and 13CNMR (1D and 2D). These procedures permitted the assignment of all chemical shifts in the diterpenoids.

Análise direta de sólidos por espectrometria de absorção atômica com atomização em forno de grafite: uma revisão

This is a review of direct analysis using solid sampling graphite furnace atomic absorption spectrometry. Greater emphasis is dedicated to sample preparation, sample homogeneity, calibration and its application to microanalysis and micro-homogeneity studies. The main advantages and some difficulties related to the applicability of this technique are discussed. A literature search on the application of solid sampling graphite furnace atomic absorption spectrometry in trace element determination in many kinds of samples, including biological, clinical, technological and environmental ones, is also presented.

Determinação simultânea de As, Cd e Pb em amostras de água purificada para hemodiálise por espectrometria de absorção atômica com forno de grafite, após otimização multivariada baseada no uso de planejamento experimental

This paper reports the development of a methodology for simultaneously determining As, Cd and Pb, employing GF AAS with polarized Zeeman-effect background correction. In order to make the procedure applicable, the influence of pyrolysis and atomization temperatures and the amount of chemical modifiers were studied. Factorial and central composite designs were used to optimize these variables. Precision and accuracy of the method were investigated using Natural Water Reference material, Nist SRM 1640. Results are in agreement with certified values at the 95% confidence limit when the Student t-test is used. This methodology was used for quality control of purified water for hemodialysis.

Processamento de pilhas do tipo botão

This work presents hydrometallurgical routes for recovering valuable elements from spent button cells, based on leaching of internal components with sulfuric acid (Li/MnO2 and Zn-air) or nitric acid (Ag-Zn), at 90 ºC for 2h. Slow evaporation of the leachate crystallized MnSO4.H2O, whereas lithium was partially recovered as LiF. Mercury present in Zn-air and Ag-Zn samples was precipitated as HgS. Silver was recovered as AgCl before mercury precipitation. Zinc and iron were precipitated as hydroxides. The amount of iron varied according to the intensity of the corrosion of the external cell case. Final wastes are neutral and colorless sodium sulfate/nitrate solutions.

Óxidos do tipo perovskita para reação de redução de no com CO

In this work, the perovskite-type oxides LaNiO3, LaMnO3, La0,7Sr0,3NiO3 and La0,7Sr0,3MnO3 were prepared by co-precipitation and tested in the NO reduction with CO at 400 and 500 ºC for 10 h. The catalysts were characterized by X-ray diffraction, temperature programmed reduction with hydrogen, nitrogen adsorption and chemical analysis. The nonstoichiometric oxygen was quantified by temperature programmed reduction, and the catalytic tests showed that the La0,7Sr0,3MnO3 catalyst presented the higher performance for the reduction reaction of NO with CO. The partial substitution of lanthanum by strontium increased the NO conversion and the N2 yield.

Estudo e caracterização da zeólita OFF Tipo T empregando diferentes fontes de silício

Offretite T zeolite was synthesized using different source of Si (Ludox AS-30, Ludox LS-30 and Aerosil 200 Degussa). The obtained materials were characterized by different complementary techniques: XRD, textural analysis by N2 adsorption, IV, SEM and chemistry analysis. This zeolite has an intermediary structure between offretite and erionite zeolites. In all experiments offretite T phase was obtained. Offretite phase presenting better crystalility are obtained in synthesis with stirring and employing aerosil as silicon source. This zeolite presents a potencial application as catalyst for hydroisodewaxing process.

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.

Determinação de corantes marcadores do tipo azo e antraquinona em combustíveis por cromatografia líquida com detecção eletroquímica

An analytical method based on high-performance liquid chromatography with electrochemical detection has been developed and applied to the determination of Solvent blue 14 (SA-14) and Solvent red 24 (SV-24) in fuel samples. The dyes were better separated on C18 column, using a mobile phase composed of acetonitrile and ammonium acetate (90:10, v/v). Detection was carried out at an oxidation potential of +0.85V. The detector response was linear at concentration range of 7.50×10-8 - 1.50×10-6 mol L-1 (r = 0.997) for SA-14 and SV-24, respectively. The method was used to quantify these dyes in fuels samples with satisfactory accuracy and precision.

Análise cristalográfica da solução sólida com estrutura tipo Tungstênio Bronze de niobato de potássio e estrôncio dopado com ferro

Solid solution of iron doped potassium strontium niobate with KSr2(FeNb4)O15-Δ stoichiometry was prepared by high efficiency ball milling method. Structural characterization was carried out by X-ray diffraction. Crystalline structure was analyzed by the Rietveld refinements using the FullProf software. The results showed a tetragonal system with the tetragonal tungsten bronze structure - TTB (a = 12.4631 (2) Å and c = 3.9322 (6) Å, V = 610.78 (2) ų). In this work, the sites occupancy by the K+, Sr2+ and Fe3+ cations on the TTB structure were determined. NbO6 polihedra distortion and its correlation with the theoretical polarization are discussed.

Desidratação de etanol sobre material nanoestruturado do tipo LaSBA-15

La-incorporated SBA-15 mesopourous molecular sieves (LaSBA-15) were directly synthesized with aim to convert ethanol to ethylene. The samples were characterized by XRD, XRF, nitrogen sorption and acidity, by thermodesorption of n-buthylamine. The results have indicated that all the samples have showed high ordered mesostructure with a large average pore size, and that the lanthanum incorporation has caused an increase in the acidity of the SBA-15. The LaSBA-15 samples have improved, with low deactivation rate, the conversion of the ethanol to water, ether, acetaldehyde and ethylene. In addition, they have increased the ethylene selectivity.

Determinação de arsênio em amostras da cadeia produtiva de frangos de corte por espectrometria de absorção atômica com forno de grafite

Chicken meat is largely consumed in human nutrition and it is produced in extremely large scale in some countries, including Brazil. In this work graphite furnace atomic absorption spectrometry was used for determination of arsenic in chicken and chicken production-related samples. These samples were digested employing a microwave-assisted procedure in closed vessels using a 7 mol L-1 nitric acid solution plus concentrated hydrogen peroxide. The concentration range of total As determined in chicken production-related samples varied from 1.30 to 29.8 mg kg-1 of As. The detection and quantification limits reached were 0.055 and 0.182 mg kg-1, respectively (n = 15).

Solubilização alcalina de peixes e otimização multivariada para determinação de chumbo e manganês usando espectrometria de absorção atômica com forno de grafite

This paper describes the development of methods for the determination of Pb and Mn in fishes by GF AAS after solubilization with tetramethylamonium hidroxide. The optimization of the operational conditions and the choice of modifier were made using multivariated optimization. Analytical Figures of Merit were adequately to propose. The Limit of Quantification obtained were 150 and 18.5 µg kg-1 to Mn and Pb, respectively. No significant difference was found between the slope values obtained for the aqueous and standard addition calibration curves. The D.P.R. was always lower than 12% and the analysis of the SRM NRCC TORT2 showed 80-120% of recovery.