Determinação de dose absorvida em feixes de elétrons utilizado câmara de ionizacão de placas paralelas

OBJETIVO: O objetivo deste trabalho foi estabelecer um procedimento para a determinação dos fatores de calibração e de doses absorvidas em feixes de elétrons. MATERIAIS E MÉTODOS: Foram utilizados um irradiador de 60Co e um acelerador linear Varian, modelo Clinac 2100C, com feixes de fótons e de elétrons. Foram estudadas câmaras de ionização do tipo dedal e de placas paralelas. RESULTADOS: Os sistemas de medidas foram submetidos aos testes preliminares (estabilidade de resposta e corrente de fuga), com resultados muito bons. Quatro métodos de calibração de câmaras de ionização para utilização em feixes de elétrons foram testados. Para a determinação da dose absorvida em feixes de elétrons foram aplicadas três metodologias propostas pela Agência Internacional de Energia Atômica, com a obtenção de resultados concordantes em quase todos os casos. CONCLUSÃO: A maior parte das câmaras de ionização estudadas mostrou-se viável, com desempenho dentro dos limites internacionais estabelecidos.

Comparação entre fatores de calibração em termos de dose absorvida no ar para uma câmara de ionização de placas paralelas

OBJETIVO: O objetivo deste trabalho foi realizar uma comparação entre os fatores de calibração em termos de dose absorvida no ar determinados em feixes gama (60Co) e de elétrons. MATERIAIS E MÉTODOS: Foram utilizados um irradiador de 60Co e um acelerador linear Varian, modelo Clinac 2100C, com feixes de fótons e de elétrons. Foram testadas uma câmara de ionização cilíndrica e três de placas paralelas. RESULTADOS: Os sistemas de medidas foram submetidos aos testes preliminares (estabilidade de resposta e corrente de fuga), com resultados muito bons. Os fatores de calibração em termos de dose absorvida no ar foram determinados utilizando-se quatro sistemas de medidas e dois tipos de objetos simuladores, com a obtenção de resultados dentro das recomendações internacionais. CONCLUSÃO: Os resultados mostraram que os fatores de calibração em termos de dose absorvida no ar obtidos para câmaras de ionização de placas paralelas, determinados em feixes de 60Co, são no máximo 1,2% mais altos que os valores obtidos em feixes de elétrons de altas energias.

Calibração multivariada para sistemas com bandas sobrepostas através da análise da fatores do tipo Q

A multivariate calibration method to determine chemical compositions of systems with severely overlapped bands is proposed. Q mode factors are determined from the spectral data and subsequently rotated using the varimax and oblique transformation of Imbrie. The method is applied to two sets of simulated data to test the sensitivity of analytical results to random experimental error. The chemical concentrations of alanine and threonine mixture are determined from spectral data of the 302,5 - 548,5 nm region.

Metodologias gerais empregadas no isolamento e identificação estrutural de feromônios de insetos

A selection of common procedures which are used for the identification and analysis of volatile biologically active compounds from insects are described.

Quimiometria I: calibração multivariada, um tutorial

The aim of this work is to present a tutorial on Multivariate Calibration, a tool which is nowadays necessary in basically most laboratories but very often misused. The basic concepts of preprocessing, principal component analysis (PCA), principal component regression (PCR) and partial least squares (PLS) are given. The two basic steps on any calibration procedure: model building and validation are fully discussed. The concepts of cross validation (to determine the number of factors to be used in the model), leverage and studentized residuals (to detect outliers) for the validation step are given. The whole calibration procedure is illustrated using spectra recorded for ternary mixtures of 2,4,6 trinitrophenolate, 2,4 dinitrophenolate and 2,5 dinitrophenolate followed by the concentration prediction of these three chemical species during a diffusion experiment through a hydrophobic liquid membrane. MATLAB software is used for numerical calculations. Most of the commands for the analysis are provided in order to allow a non-specialist to follow step by step the analysis.

Redes neurais e suas aplicações em calibração multivariada

Neural Networks are a set of mathematical methods and computer programs designed to simulate the information process and the knowledge acquisition of the human brain. In last years its application in chemistry is increasing significantly, due the special characteristics for model complex systems. The basic principles of two types of neural networks, the multi-layer perceptrons and radial basis functions, are introduced, as well as, a pruning approach to architecture optimization. Two analytical applications based on near infrared spectroscopy are presented, the first one for determination of nitrogen content in wheat leaves using multi-layer perceptrons networks and second one for determination of BRIX in sugar cane juices using radial basis functions networks.

O conceito de incerteza aplicado aos processos de medição associados à preparação de uma solução de referência para calibração

The implementation of a quality assurance program in chemical analytical laboratories, that can aid in demonstrate the quality of their results, is an issue of great concern. As a consequence, it is mandatory to give an estimate of the confidence that can be placed on the obtained results. An useful measure of this confidence is the measurement uncertainty and, nowadays, a result without the corresponding uncertainty statement cannot be considered reliable. This paper presents a summary of the most important mechanisms for the evaluation and reporting of the measurement uncertainty. In implementing these principles, it is described the measurement uncertainty estimation associated with the preparation of a uranium elemental reference solution at 2.4 mg.kg-1 from the corresponding certified reference material (in this example at 1003 mg.kg-1).

Comparação de metodologias para a determinação de umidade em geléia real

The aim of this paper was to compare methods of moisture determination to choose the best one for the determination of this parameter in royal jelly samples. Royal jelly is sensitive to high temperatures becoming dark and loosing volatiles in high temperatures. The methods were: vacuum oven at 60 ºC, 70 ºC, conventional oven at 105 ºC, Karl Fisher, dissecator with sulfuric acid and dryness with infrared light at 105 ºC. Based on the results, the best method was the dissecator with sulfuric acid for moisture determination in royal jelly.

Aplicação de metodologias FTIR de transmissão e fotoacústica à caracterização de materiais altamente energéticos: parte II

Materials obtained during the synthesis of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) were characterized by Fourier transform infrared (FTIR) transmission spectroscopy and/or Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS). By these techniques the spectrometric alterations that occurred during the process were observed. The characterized species during the synthesis of HMX were alpha-HMX, beta-HMX, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and HMX/RDX mixtures. The FTIR-PAS was verified to be a promising technique of great usefulness of the characterization of highly energetic materials because it is fast, simple and requires no sample preparation unlike Fourier transform infrared transmission technique (KBr pellet). The FTIR-PAS analysis showed that with small sample quantity is possible to distinguish between thealpha-HMX and beta-HMX and to detect even in a qualitative way different HMX / RDX ratios.

Recomendações para calibração em química analítica: parte I. Fundamentos e calibração com um componente (calibração univariada)

This paper is a translation from IUPAC nomenclature document by K. Danzer and L. A. Currie (Pure Appl. Chem., 1998, 70(4), 993-1014). Its goal is to establish an uniform and meaningful approach to terminology (in Portuguese), notation, and formulation for calibation in analytical chemistry. In this first part, general fundamentals of calibration are presented, namely for both relationships of qualitative and quantitative variables (relations between variables characterizing certain types analytes of the measured function on the other hand and between variables characterizing the amount or concentration of the chemical species and the intensities of the measured signals, on the other hand). On this basis, the fundamentals of the common single component calibration (Univariate Calibration) which models the relationship y = f(x) between the signal intensities y and the amounts or concentrations x of the analyte under given conditions are represented. Additional papers will be prepared dealing with extensive relationships between several intensities and analyte contents, namely with multivariate calibrations and with optimization and experimental design.

Vinte e cinco anos de reações, estratégias e metodologias em Química Orgânica

An overview of the developments that occurred in the field of organic chemistry in Brazil in the last 25 years is presented. These developments are briefly compared to those observed worldwide, including some modern trends. The main source of information was the annual meeting of the Brazilian Chemical Society (RASBQ) covering the period 1979-2001 and the biennial Brazilian Meeting on Organic Synthesis (BMOS). All the contributions presented at these two meetings were classified according to six main indicatives, to permit a discussion about the past, present and future activities of Organic Chemistry in Brazil.

Metodologias de síntese de 2-arilcicloexanonas

Several methodologies concerning the preparation of 2-aryl and 2-heteroarylcyclohexanones are presented. The use of these intermediates in the synthesis of chemically and biologically interesting organic compounds is also discussed.

Modelo de calibração da concentração de metilmetacrilato em solução aquosa utilizando espectroscopia de absorção no ultravioleta

Dilutions of methylmetacrylate ranging between 1 and 50 ppm were obtained from a stock solution of 1 ml of monomer in 100 ml of deionised water, and were analyzed by an absorption spectrophotometer in the UV-visible. Absorbance values were used to develop a calibration model based on the PLS, with the aim to determine new sample concentrations. The number of latent variables used was 6, with the standard errors of calibration and prediction found to be 0,048 ml/100 ml and 0,058 ml/100 ml. The calibration model was successfully used to calculate the concentration of monomer released in water, where complete dentures were kept for one hour after polymerization.

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.

Comparação de duas metodologias de amostragem atmosférica com ferramenta estatística não paramétrica

In atmospheric aerosol sampling, it is inevitable that the air that carries particles is in motion, as a result of both externally driven wind and the sucking action of the sampler itself. High or low air flow sampling speeds may lead to significant particle size bias. The objective of this work is the validation of measurements enabling the comparison of species concentration from both air flow sampling techniques. The presence of several outliers and increase of residuals with concentration becomes obvious, requiring non-parametric methods, recommended for the handling of data which may not be normally distributed. This way, conversion factors are obtained for each of the various species under study using Kendall regression.