Excitação eletrônica das moléculas de metacrilato de metila e estireno na região do ultravioleta de vácuo

Angle-resolved electron energy-loss spectra have been measured for the methyl methacrylate (MMA) and styrene molecules in the 0 - 50 eV energy range. The spectra have been obtained at 1 keV incident energy, with an energy resolution of 0.8 eV and covering an angular range of 2.0 to 7.0 degrees. Within our knowledge, this is the first gas-phase excitation spectrum for MMA and styrene in this energy range. The spectra of MMA at small scattering angles are dominated by an intense peak at 6.7 eV followed by a broad band centered at about 16 eV. In the case of styrene, six bands can be observed in the spectra. Based on the angular behaviour of the excitation spectra of these molecules, the low-lying peaks observed are considered to be associated predominantly with dipole-allowed processes. In both cases, new bands can be observed for excitation energies greater than 20 eV. This could be associated with dipole-forbidden transitions to shake-up and doubly-excited states.

Porta-amostras polimérico para espectroscopia infravermelha de sistemas líquidos aquosos ou orgânicos

Infrared spectroscopy laboratories works under permanent care with respect to water contamination, mainly in liquid samples. In this case crystal plates destruction or damage are frequent, increasing the operational expenses. On the other hand, the laboratory which produces such samples must be very careful in drying liquid samples. In this work we develop a simple and inexpensive way to operate in such conditions using polypropylene and HDPE films which were thermally soldered resulting little containers or sample holders. The spectra of sample/sample holder is achieved having the sample holder as background.

Preparo de óxido de nióbio suportado em alumina por deposição química em fase vapor: caracterização por espectroscopia vibracional e termogravimetria

Alumina supported niobium oxide was prepared by chemical vapor deposition (CVD) of NbCl5. The alumina was calcined and pretreated at differents temperatures in order to vary the density of OH groups on the surface which was determined by thermogravimetric analysis. A good correlation was found between the amount of anchored niobium and the total number of anionic sites (oxide and hydroxyl groups) on the surface of the alumina. The infrared spectra on the OH stretching region indicate that OH groups coordinated to at least one tetrahedral aluminum were more reactive towards NbCl5.

Nova rota de preparação do 2-cloro-1,3,2-dioxofosfolana e 2-cloro-4,5-benzo-1,3,2-dioxofosfolana e caracterização por espectroscopia de RMN multinuclear

A new method for the preparation of 2-chloro-1,3,2-dioxaphospholane (1) and 2-chloro-4,5-benzo-1,3,2-dioxaphospholane (2), are reported. The modifications introduced in the synthetic route improved the yield and facilitated the control of reaction, but the synthesis require longer reaction time. The compounds were characterized by ¹H, 13C{¹H} and31P{¹H} NMR spectroscopy. Due to the complexity of the spin system AA'BB'X (A, A', B, B' = ¹H; X = 31P) of 2, a simulation of the ¹H NMR spectra was done and it's in agreement with the bibliography.

Espectroscopia óptica de vidros fluoroindatos dopados com íons Er3+ e Yb3+

Optical spectroscopy in the 400-1700nm wavelength range was performed on rare earth doped heavy metal fluoride (HMF) glasses. In the present work In-based fluoride glasses with a fixed 2 mol % YbF3 concentration and an ErF3 content ranging from 0 to 8 mol % were investigated. According to the experimental spectroscopic data a dependence in the absorption coefficient, the photoluminescence intensity and in the radiative lifetime could be verified as a function of the ErF3 content. In addition, at liquid nitrogen temperature, light emission corresponding to indirect transitions in the infrared energy range could be easily observed as a consequence of the low phonon frequency characteristic of this class of fluoride glasses. For all the studied compositions, strong upconversion to the green and red light was observed by pumping these Er3+- and Yb3+-doped HMF glasses with 790 and 980nm photon sources.

Estudo por espectroscopia no infravermelho da interação metal-suporte em Pt/TiO2. A influência da adsorção de hidrogênio

The influence of the presence of hydrogen on Pt/TiO2 catalysts submitted to reduction treatment has been studied by FT-IR at room temperature. After submitting to LTR treatment, the hydrogen spillover has been detected and the presence of hydrogen at the bulk is shown to produce a strong absorption in the infrared spectral region. After HTR treatment, the hydrogen is strongly chemissorbed.

Aplicação de algoritmos genéticos na seleção de variáveis em espectroscopia no infravermelho médio: determinação simultânea de glicose, maltose e frutose

Genetic algorithm was used for variable selection in simultaneous determination of mixtures of glucose, maltose and fructose by mid infrared spectroscopy. Different models, using partial least squares (PLS) and multiple linear regression (MLR) with and without data pre-processing, were used. Based on the results obtained, it was verified that a simpler model (multiple linear regression with variable selection by genetic algorithm) produces results comparable to more complex methods (partial least squares). The relative errors obtained for the best model was around 3% for the sugar determination, which is acceptable for this kind of determination.

Espectroscopia vibracional: sistemática para o cálculo dos estiramentos CO de complexos carbonílicos e determinação da sua atividade IV e Raman

IR bands related to M-C stretchings are not diagnostically significant for the identification of carbonyl groups in the spectra of carbonyl complexes. Otherwise, the frequency, intensity and number of bands for the CO stretchings provide very useful informations about the number of CO ligands and many others structural proprieties, like the presence of bridged CO groups. We report about a relatively simple and useful method for the determination of the CO stretchings of carbonyl complexes, which considers only the bond stretching internal coordinates of the CO groups.

Aplicação de alguns modelos quimiométricos à espectroscopia de fluorescência de raios-X de energia dispersiva

The objective of this work was to accomplish the simultaneous determination of some chemical elements by Energy Dispersive X-ray Fluorescence (EDXRF) Spectroscopy through multivariate calibration in several sample types. The multivariate calibration models were: Back Propagation neural network, Levemberg-Marquardt neural network and Radial Basis Function neural network, fuzzy modeling and Partial Least Squares Regression. The samples were soil standards, plant standards, and mixtures of lead and sulfur salts diluted in silica. The smallest Root Mean Square errors (RMS) were obtained with Back Propagation neural networks, which solved main EDXRF problems in a better way.

Aplicação da espectroscopia de ressonância magnética nuclear para estudos de difusão molecular em líquidos: a técnica DOSY

Diffusion coefficients provide uniquely detailed and easily interpreted information on molecular organization and phase structure. They are quite sensitive to structural changes, and to binding and association phenomena, in particular for liquid colloidal or macromolecular systems. This paper describes the principles of diffusion measurements in liquids by pulsed magnetic field gradient spin-echo (PFG-SE) NMR spectroscopy. The important PFG-SE technique known as DOSY is presented and discussed. This is a noninvasive technique that can provide individual multicomponent translational diffusion coefficients with good precision in a few minutes, without the need for radioactive isotopic labelling.

Métodos Ultravioleta Selectivo y de reducción con Hidracina en la determinación del ión nitrato an aguas subterraneas

In this study, a comparison of two methods, the Selective UV Spectrophotometrical Method and Reduction with Hidrazine Method, for the determination of Nitrate ion in groundwater, was carried out. For this purpose, the results from all the drinking water collectings of the city of Olavarría, Argentina, were employed. Both methods present significant different means, but they don´t present significant differences in their variances.

O uso de radiação ultravioleta para o pré-tratamento de amostras em análise inorgânica

The basic principles of UV irradiation as sample pre-treatment step and its potential for inorganic analysis are illustrated and discussed through significant examples from the literature. Not only does this overview cover the classical applications of this technique in the decomposition of organic matter in electroanalysis, but it also presents recent trends, including the increasing interest in employing UV irradiation in flow analytical systems, successful attempts to enhance its effectiveness and the coupling with chromatographic and spectroscopic methodologies. Furthermore, a number of relevant cases of UV-driven derivatization reactions involving photo-sensitive inorganic species are presented, showing some convenient options to perform fast and reliable determination of inorganic and organic analytes.

Determinação da concentração micelar crítica de ácidos húmicos por medidas de condutividade e espectroscopia

The aim of this study was the determination of the critical micelle concentration (CMC) of the sodium dodecyl sulfate (SDS) surfactant using spectroscopic and conductimetric determinations and to compare these methodologies in the determination of the CMC of different humic acids (HA). The CMC obtained by conductimetric determination was satisfactory. By spectroscopic determination two values of the CMC were obtained for HA. These values can be to due the intra and intermolecular interactions in the HA structure.

Validação de modelos de calibração multivariada: uma aplicação na determinação de pureza polimórfica de carbamazepina por espectroscopia no infravermelho próximo

The application of analytical procedures based on multivariate calibration models has been limited in several areas due to requirements of validation and certification of the model. Procedures for validation are presented based on the determination of figures of merit, such as precision (mean, repeatability, intermediate), accuracy, sensitivity, analytical sensitivity, selectivity, signal-to-noise ratio and confidence intervals for PLS models. An example is discussed of a model for polymorphic purity control of carbamazepine by NIR diffuse reflectance spectroscopy. The results show that multivariate calibration models can be validated to fulfill the requirements imposed by industry and standardization agencies.

Montagem de câmara com lâmpada de ultravioleta de baixo custo

Thin layer chromatography is a quick, inexpensive and effective way of screening mixtures of non-volatile organic compounds and it is highly recommended for analytical studies. Inspection of plates under ultraviolet light for the detection of colourless compounds should be performed before any further chemical methods are applied. Construction of a low-cost UV-viewing cabinet with lamp employing parts easily found on the local market is described.