Química combinatória de materiais com análise por microdifração de raios X. Primeira parte: fundamentos

Combinatorial chemistry refers to techniques to rapidly fabricate tens, hundreds or even thousands of different micro samples. The analysis of the large number of samples generated by combinatorial methods requires highly efficient analytical methods. In this case, the challenges are due not only to the large number of samples to be analyzed, but also to the small amount of sample available for analysis. This paper describes the fundamentals of combinatorial chemical methods applied to discover of materials and the development in x-ray diffraction to analyze micro samples.

Catalisador Pd/gama-Al2O3: efeito do tamanho de partícula na atividade catalítica para combustão do CH4

Methane, the main constituent of natural gas (> 85%), is employed in large scale as an energy source (thermoelectric power plants, automobiles, etc). However, significant quantities of this gas contribute to the greenhouse effect. The catalytic combustion of methane can minimize these emissions. Palladium is one of the metals that shows the highest activity, depending on the different active forms of the metal. In this article, we focus on the influence of particle size and pretreatment on the catalytic performance of palladium in the methane combustion reaction.

Preparação de amostra de fígado bovino e estudo de micro homogeneidade para a determinação de Cd E Pb por espectrometria de absorção atômica com atomização eletrotérmica e amostragem direta de sólido

This work describes a systematic study for bovine liver sample preparation for Cd and Pb determination by solid sampling electrothermal atomic absorption spectrometry. Samples were prepared using different procedures: (1) drying in a household microwave oven followed by drying in a stove at 60 ºC until constant mass, and (2) freeze-drying. Ball and cryogenic mills were used for grinding. Particle size, sample size and micro sample homogeneity were investigated. All prepared samples showed good homogeneity (He < 10) even for low sample mass, but samples dried in a microwave oven/stove and ground in a ball mill presented the best homogeneity.

Espectrometria de massas com ionização por "electrospray": processos químicos envolvidos na formação de íons de substâncias orgânicas de baixo peso molecular

An overview of the current literature on the chemical processes involved in the ion formation from low molecular weight organic compounds by electrospray ionization mass spectrometry is given.

Análise quiral por espectrometria de massas através da utilização do método cinético

Novel and quantitative mass spectrometry methods for rapid and accurate enantiomeric excess determination are presented. These methodologies use electrospray ionization (ESI) and mass spectrometry (MS) to detect and analyze, via collision-induced dissociation (CID), mass-selected transition metal complexes that promote enantio especific interactions. The data from CID are conveniently treated by the kinetic method, a sensitive linear free energy method of treating mass spectrometric results. Four different variations of this methodology are described: single ratio method (S R), quotient ratio method (Q R), fixed ligand method (S Rfixed), and quotient ratio method with fixed ligand (Q Rfixed). These individual methods are compared and their main features discussed in detail.

Determinação de resíduos de cloranfenicol em amostras de leite e mel industrializados utilizando a técnica de espectrometria de massas em "tandem" (CLAE-EM/EM)

The present work shows a method for the determination of chloramphenicol (CAP) antibiotic in milk, powder milk and honey. The solid phase extraction and liquid-liquid extraction were applied as a clean-up and pre-concentration strategies followed by LC-ESI/MS/MS analysis. The recovery was studied for different fortification levels from 0.05 to 1.00 µg L-1 in milk, showing values between 91 101% and RSD bellow 8.0%, while honey was spiked with a concentration of 0.20 µg kg-1 yelding a mean recovery of 83% and RSD of 6.5%. The quantification transition 321>152 showed a LOD of 0.52 ng kg-1 and LOQ of 1.85 ng kg-1.

Elucidando os estados de oxidação do nitrogênio através da espectroscopia de absorção de raios-X na borda K do nitrogênio

The potentialities of X-ray Absorption Near Edge Spectroscopy (XANES) of the N K edge (N K) obtained with the spherical grating monochromator beam line at the Brazilian National Synchrotron Light Laboratory are explored in the investigation of poly(aniline), nanocomposites and dyes. Through the analysis of N K XANES spectra of conducting polymers and many other dye compounds that are dominated by 1s®p* transitions, it was possible to correlate the band energy value with the nitrogen oxidation states. An extensive N K XANES spectral database was obtained, thus permitting the elucidation of the nature of different nitrogens present in the intercalated conducting polymers.

Um novo método para quantificar mercúrio orgânico (Hg orgânico) empregando a espectrometria de fluorescência atômica do vapor frio

In this work a simple and sensitive procedure to extract organic mercury from water and sediment samples, using methylene chloride in acidic media followed by CVAFS quantification has been developed. The method was evaluated for possible interferents, using different inorganic mercury species and humic acid, no effects being observed. The detection limit for organic mercury was 160 pg and 396 pg for water and sediment samples respectively. The accuracy of the method was evaluated using a certified reference material of methylmercury (BCR-580, estuarine sediment). Recovery tests using methylmercury as surrogate spiked with 1.0 up to 30.0 ng L-1 ranged from 90 up to 109% for water samples, whereas for sediments, recoveries ranged from 57 up to 97%.

Pré-concentração de cádmio com Saccharomyces cerevisiae e determinação em águas fluviais usando espectrometria de emissão óptica com plasma indutivamente acoplado

A preconcentration method based on the use of Saccharomyces cerevisiae as sorbent material is proposed for the determination of Cd(II) in river water. The solid phase extraction was performed in batch mode and the determination of the analyte in the solid phase was easily carried out by introducing a slurry of the yeast (0.0625 g / 2.5 mL) directly into the ICP OES. A limit of detection of 0.11 µg L-1 and a sample throughput in the range of 4 - 54 sample h-1 were obtained. Determinations of cadmium in a certified sample and in real river water samples were in excellent agreement with the expected values.

Produção de hidrogênio a partir da reforma a vapor de etanol utilizando catalisadores Cu/Ni/gama-Al2o3

Cu/Ni/gamma-Al2O3 catalysts were prepared by an impregnation method with 2.5 or 5% wt of copper and 5 or 15% wt of nickel and applied in ethanol steam reforming. The catalysts were characterized by atomic absorption spectrophotometry, X-ray diffraction, temperature programmed reduction with hydrogen and nitrogen adsorption. The samples showed low crystallinity, with the presence of CuO and NiO, both as crystallites and in dispersed phase, as well as of NiO-Al2O3. The catalytic tests carried out at 400 ºC, with a 3:1 water/ethanol molar ratio, indicated the 5Cu/5Ni/Al2O3 catalyst as the most active for hydrogen production, with a hydrogen yield of 77% and ethanol conversion of 98%.

Análise arqueométrica de cerâmica Tupiguarani da região central do Estado do Rio Grande do Sul, Brasil, usando fluorescência de raios X por dispersão de energia (EDXRF)

Energy dispersive X-ray fluorescence methodology (EDXRF) was used to determine Al, Ba, Ca, Cr, Fe, K, Mn, Pb, Rb, S, Si, Sr, Ti, V, Zn in pottery sherds from seven archaeological sites in the central region of Rio Grande do Sul State, Brazil. The potteries' chemical fingerprints from Ijuí River, Ibicuí Mirim River, Vacacaí Mirim River and Jacuí River were identified. Interactions between sites from the Jacuí River, Vacacaí Mirim River and Ibicui Mirim River could have occurred because some samples from these sites are overlapping in a principal component analysis (PCA) graphic. The pottery provenance could be the same.

Determinação experimental dos raios cristalográficos dos íons sódio e cloreto

This experiment, where very common materials and equipments are used, conducts to good and interesting results related to the ionic radii of sodium and chloride ions. It also offers an excellent opportunity to discuss the crystalline arrangement of solids and to apply simple mathematical tools for calculations. Other important concepts such as density, solubility and saturated solution are also used. The simplicity of the experiment creates an excellent opportunity for reasoning with the students about the technique.

Síntese da hidroxiapatita e refinamento estrutural por difração de raios-x

A sample of hydroxyapatite was synthesized and its crystalline structure was analyzed by X-ray diffraction by means of the Rietveld method. Two functions were used to fit the peak profiles, modified Voigt (TCHZ) and Pearson VII. The occupational factors and lattice parameters obtained by both models show that the sample does not contain relevant cationic substitutions. The interatomic distances from Ca1 to oxygens O1, O2 and O3 were adequate for a pure hydroxyapatite without defect at site Ca1. Besides, the use of multiple lines in planes (300) and (002) associated with the model Pearson VII resulted in good agreement with the TCHZ model with respect to the size-strain effectswith an ellipsoidal shape of crystallites. In conclusion, the procedures adopted in the synthesis of hydroxyapatite produced a pure and crystalline material. The experimental results of transmission electron microscopy confirmed the predicted shape of crystals.

Desenvolvimento e validação de metodologia de análise de misturas biodiesel: diesel utilizando cromatografia gasosa-espectrometria de massas

The aim of this work was to develop and validate a method of analysis of biodiesel:diesel blends using HRGC-MS in SIM mode. The proposed method is applicable to biodiesel from linoleic oils, such as soybean oil. The following results were obtained: linearity over the methyl linoleate concentration range of 250-2500 mg L-1 (R² > 0.999); limits of detection and quantification of 2 and 5 mg L-1, respectively; recovery from 82 to 96% of biodiesel in diesel and repeatability < 2% (RSD). Comparison between two operators showed that it is not necessary the same operator to do the analysis.

Estudo de coprólito da bacia sedimentar do Araripe por meios de espectroscopia FT-IR e difração de Raios-X

Coprolites are fossilized faeces that constitute an important source of palaeobiological informations. This paper describes the characterization of some coprolite materials originated from the Romualdo Member of the Santana Formation (Araripe Basin, south of Ceará State in Brazil) by means of two techniques: X-ray powder diffraction and Fourier transform infrared spectroscopy (FT-IR). This characterization allowed us to determine the main composition of the coprolites, of the nodulus (where the coprolites were extracted) and of the sediment (where the nodulus was found) suggesting that the material was produced by a carnivorous fish of the Lower Cretaceous.