Helga Gabriela Aleme

Multivariate curve resolution combined with gas chromatography to enhance analytical separation in complex samples: a review.

This review describes the major advantages and pitfalls of iterative and non-iterative multivariate curve resolution (MCR) methods combined with gas chromatography (GC) data using literature published since 2000 and highlighting the most important combinations of GC coupled to mass spectrometry (GC-MS) and comprehensive two-dimensional gas chromatography with flame ionization detection (GC×GC-FID) and coupled to mass spectrometry (GC×GC-MS). In addition, a brief summary of some pre-processing strategies will be discussed to correct common issues in GC, such as retention time shifts and baseline/background contributions. Additionally, algorithms such as evolving factor analysis (EFA), heuristic evolving latent projection (HELP), subwindow factor analysis (SFA), multivariate curve resolution-alternating least squares (MCR-ALS), positive matrix factorization (PMF), iterative target transformation factor analysis (ITTFA) and orthogonal projection resolution (OPR) will be described in this paper. Even more, examples of applications to food chemistry, lipidomics and medicinal chemistry, as well as in essential oil research, will be shown. Lastly, a brief illustration of the MCR method hierarchy will also be presented.

Determination of disease biomarkers in Eucalyptus by comprehensive two-dimensional gas chromatography and multivariate data analysis

In this paper is reported the use of the chromatographic profiles of volatiles to determine disease markers in plants - in this case, leaves of Eucalyptus globulus contaminated by the necrotroph fungus Teratosphaeria nubilosa. The volatile fraction was isolated by headspace solid phase microextraction (HS-SPME) and analyzed by comprehensive two-dimensional gas chromatography-fast quadrupole mass spectrometry (GC×GC-qMS). For the correlation between the metabolic profile described by the chromatograms and the presence of the infection, unfolded-partial least squares discriminant analysis (U-PLS-DA) with orthogonal signal correction (OSC) were employed. The proposed method was checked to be independent of factors such as the age of the harvested plants. The manipulation of the mathematical model obtained also resulted in graphic representations similar to real chromatograms, which allowed the tentative identification of more than 40 compounds potentially useful as disease biomarkers for this plant/pathogen pair. The proposed methodology can be considered as highly reliable, since the diagnosis is based on the whole chromatographic profile rather than in the detection of a single analyte.

Determination of ethanol and specific gravity in gasoline by distillation curves and multivariate analysis

The partial least-squares regression method (PLS) was employed to predict the amount of ethanol and specific gravity in automotive gasoline using distillation curves (ASTM-D86). Additionally, a comparison was made between regression coefficients of all the algorithms, after selecting the number of latent variables. The low values obtained for RMSEC and RMSEP, associated with high accuracy when compared to the standard methodologies (NBR-13992, ASTM-D4052 and D1298) showed that PLS was efficient to determine the ethanol content and specific gravity in gasoline, since the model contains samples of different gasoline compositions, thus reflecting the variety of fuel in the Brazilian market. In addition, the proposed method is low cost, time reducing and easy to implement, as it utilizes the results of a routine assay carried out to evaluate the quality of automotive fuel.

As práticas educativas e seus personagens na visão de estudantes recém-ingressados nos cursos de Química e Biologia

Resumo: Desenvolvemos o presente trabalho com o objetivo de identificar concepcoes sobre as relacoes em sala de aula apresentadas por alunos recem-ingressados nos cursos de Quimica e Biologia. Baseados em Bruner, usamos a narrativa como instrumento investigativo dessas concepcoes, solicitando aos alunos que se imaginassem professores e relatassem como seria um dia de suas vidas. Pela analise dos relatos, percebemos que o professor e aquele que estuda e se prepara para as aulas, transmite conhecimentos, motiva, contextualiza, tem uma boa relacao com os alunos e e admirado por eles. Alem disso, esse professor e considerado um profissional em tempo integral, trabalhando, sobretudo, no Ensino Medio, com alunos interessados e atenciosos. Entender como essas concepcoes se formaram e problematiza-las na formacao inicial e importante. Palavras-chave: Ensino de Quimica. Ensino de Biologia. Relacoes em sala de aula. Narrativas. Concepcoes.

Ensinar e aprender Química: a percepção dos professores do Ensino Médio

O presente trabalho buscou investigar a percepcao dos professores da educacao basica sobre as praticas pedagogicas em sala de aula e na escola, as dificuldades enfrentadas e as possiveis maneiras de soluciona-las, assim como as formas por eles utilizadas para se manterem atualizados. A investigacao envolveu 93 professores do Ensino Medio de escolas do estado de Minas Gerais, durante a realizacao da Olimpiada Mineira de Quimica (OMQ) 2008. A analise dos comentarios feitos pelos professores, no instrumento de coleta de dados utilizado, mostrou que os mesmos tendem a associar as dificuldades que enfrentam principalmente a escola, aos alunos e a questoes externas a escola, ou seja, nao se assumem como parte dos problemas. Percebemos, tambem, que associam as principais melhorias na educacao basica a infra-estrutura da escola e que nem todos participaram de eventos que promovessem a atualizacao profissional nos ultimos dois anos.

Análise quimiométrica usando RMN de 13C como ferramenta para diferenciar duas espécies de Maytenus

Maytenus robusta foi recentemente sinonimizada com Maytenus gonoclada devido a sobreposicao de caracteres morfologicos utilizados na classificacao botânica. O presente estudo investiga as diferencas quimicas entre robusta Maytenus gonoclada e Maytenus robusta usando analise quimiometrica. Os dados de RMN de 13 C de triterpenos pentaciclicos obtidos a partir dessas especie foram avaliados por meio da Analise de Componentes Principais (PCA) e os friedelanes foram os metabolitos que mais contribuiram para as diferencas entre as duas especies. Isso demonstra a analise quimiometrica como uma ferramenta importante para esclarecer a taxonomia de plantas semelhantes.

Professor de ensino superior: o entendimento a partir de narrativas de pós-graduandos em química

The quality of higher education has raised growing interest among researchers and experts in education. In the present work we have emphasized the correlation between the growing specialization offered by graduate programs in Chemistry and the improvement in the quality of university teachers, trying to understand how the graduate students themselves imagine the teaching activity. For that, graduate students in Chemistry from the Federal University of Minas Gerais were invited to construct narratives about a fictitious situation in which they imagined themselves as teachers. The analysis of the reports was made by grouping the facts described under three categories: the preparation for approval in the admission exam, the classes taught, and the activities developed during the first four months of work. Results have shown that students pay less attention to the teaching activity and tend to value research and the activities that foster it. This shows that future professionals, even taking up the post of teachers, are more predisposed to act as researchers than to exercise the teaching activity. Such indication seems to be related to the demands made during the selection process for higher education teachers and to the current work situation in most universities, which evaluate qualitatively the intellectual production in the form of articles, whereas classes are evaluated in a more quantitative manner.