Controle de autenticidade de óleos de copaíba comerciais por cromatografia gasosa de alta resolução

Copaiba oil is a resin extracted from the trunk of trees of Copaifera species which grow in Brazil where it is widely used in popular medicine as an anti-inflammatory, antiseptic anti-bactericidal, diuretic, dermatological, expectorant, and anti-infective. The comparative study of the composition of commercial copaiba oils was carried out by high resolution gas chromatography (HRGC) and high resolution gas chromatography-mass spectrometry (HRGC-MS) analysis. The commercial oils were compared with authentic oils, collected from the southeast and northern regions of Brazil. Sixteen commercial oils were analysed and two of them revealed adulterations with fatty acids. Using the chromatographic profile of authentic copaiba species oils, it is possible to analyse commercial oils and determine the authenticity of these materials.

Principais substâncias responsáveis pelo aroma de mangas comerciais brasileiras identificadas por cromatografia gasosa de alta resolução/olfatometria/espectrometria de massas

Six Brazilian commercial mangoes were analysed by HRGC-O-AEDA-MS, viz., Carlota, Haden, Espada, Coração de boi, Rubi and Tommy Atkins. All them showed ethyl butanoate as the main aroma character impact compound by AEDA evaluation. The ethyl esters of 2 and 3-methylbutanoic acids are also important, the main contribution in Carlota variety being 2(S) enantiomer. In Rubi variety, both 2(R) enantiomer and 3-methyl isomer contributes to the caprylic fruity note observed. In four varieties, viz., Haden, Espada, Rubi and Tommy Atkins, d-3-carene showed to be the second impact aroma compound presented. In Tommy Atkins variety, a-pinene also has a significant contribution, mainly due to its (1R,5R)(+)-enantiomer.

Elementos da dinâmica química ao nível da teoria variacional do estado de transição com correções interpoladas

In this article are presented some fundamental elements of the conventional and of the variational transition state theories which are needed to carried out calculations of semi-classical chemical dynamics. Some important bottlenecks in building reliable potential energy surfaces using electronic structure calculations are also discussed. It is put emphasis on the methodology of the variational transition state theory with interpolated corrections (VTST-IC), and its application in the calculations of the rate constants and of the kinetic isotope effect (KIE) of CH4 + Cl « CH3 + HCl reaction.

Estado da arte da cromatografia gasosa de alta resolução e alta temperatura

The developments in stationary phase synthesis and capillary column technology, have opened new perspectives in analysis of high molecular mass compounds (³600 daltons) and thermolabile organic compounds by High Temperature High Resolution Gas Chromatography (HT-HRGC). HT-HRGC is a new analytical borderline and its application to the analysis of high molecular mass compounds is still in its infancy. The apolar and medium polar gum phases can now be operated at temperatures up to 400-480ºC, being used for the analysis of n-alcanes up to C-100, lipids, oligosaccharides, industrial resins, polyglycerols, cyclodextrins, porphyrins, etc. This technique should play a leading role as a powerful tool, for many different analysis types, in multidisciplinary fields of Science.

Combinación de sistemas de flujo de baja y alta presion para la determinacion de Mg, Ca y Sr en salmueras por espectrofotometria de absorcion atomica con llama

This article describes the combination of low- and high-pressure flow systems for the determination of Magnesium, Calcium and Strontium by flame atomic absorption spectrometry (FAAS). In the low-pressure system a short C-18 RP column (length 0,5 cm) was utilized for the preconcentration/matrix separation step, xylenol orange was used as chelating agent and tetrabutylamonium acetate for ion pair formation. The hydraulic high pressure nebulization (HHPN) was used for sample transport and sample introduction in the high pressure system. The repeatabilities and detection limits for Mg, Ca and Sr were determined and compared with those obtained by pneumatic nebulization (PN). The results show that the detection limits obtained using the HHPN for Mg, Ca and Sr are between 1.5 to 2 times better than those obtained by PN when the signal transient was measured in area. The system presented a sampling frequency of 130 h-1 for direct determination of Mg, Ca or Sr in samples of saturated sodium chloride used in the production of chlorine and sodium hydroxide.

A dinâmica de analisar livros didáticos com os professores de química

This work evidences a survey conducted during a teacher professional qualification in Rio Grande do Sul, Brazil. This survey analysed the textbooks used by these teachers. The dynamics consisted of choosing the analytic criteria used by teachers, and adding new criteria for examining their difficulties and ways to choose textbooks. This article emphasises the problematics and difficulties teachers have to make choices and their loss of skills and authority to consider these books more profoundly.

Um potencial de interação para o estudo de materiais e simulações por dinâmica molecular

The Vashishta-Rahman effective interaction potential, based on the Pauling's concept of "ionic radii", has been successfully employed to investigate structural and dynamical properties of different classes of material. By celebrating Pauling's birth centenary, we review the building up of the Vashishta-Rahman potential and we present molecular-dynamics simulation results for structure and dynamics of superionic materials, chalcogenide glasses and metallic oxides.

Dinámica de reacciones unimoleculares en fase gas: Desviaciones del comportamiento estadístico

The present review summarizes the most relevant results of our research group obtained recently in the field of unimolecular reaction dynamics. The following processes are specifically analyzed: the isomerization, dissociation and elimination in methyl nitrite, the fragmentation reactions of the mercaptomethyl cation, the C-CO dissociation in the acetyl and propionyl radicals, and the decomposition of vinyl fluoride. In all the cases, only state- or energy-selected systems are considered. Special emphasis is paid to the possibility of systems exhibiting non-statistical behavior.

Fases estacionárias para cromatografia líquida de alta eficiência em fase reversa (CLAE-FR) baseadas em superfícies de óxidos inorgânicos funcionalizados

Particles of porous silica or other solvent resistent inorganic oxides can be functionalized by aliphatic (e.g., C-8 or C-18) or other groups to give stationary phases for use in reversed phase HPLC. The functionalization can be done by bonding of individual groups to the surface of the support particles, by producing an organic polymeric film from pre-polymers, or by adsorbing/immobilizing pre-formed polymers on the surfaces. These three types of functionalization are reviewed.

Determinação de alfa-Tocoferol em alho irradiado utilizando cromatografia líquida de alta eficiência (CLAE)

The effects of 60Co ionizing radiations in doses of 0, 75, 100, 150, 200 and 250Gy on garlic, upon the alpha-tocopherol concentration were studied. The alpha-tocopherol contents were established by high performance liquid chromatography (HPLC), after direct hexane extraction from the garlic samples. The alpha-tocopherol was determined through normal-phase column, and mobile phase was composed by hexane: iso-propyl alcohol (99:01 v/v), with 2mL/min flow rate and fluorescence detector. It is statistically shown that an irradiation dose of up to 150 Gy does not affect the garlic alpha-tocopherol content.

Determinação de compostos de massa molecular alta em folhas de plantas da Amazônia

The fractIons of dichloromethane extracts of leaves from andiroba (Carapa guianensis - Meliaceae), caapi (Banisteriopsis caapi - Malpighiaceae), cocoa (Theobroma cacao - Sterculiaceae), Brazil nut (Bertholletia excelsa - Lecytidaceae), cupuaçu (Theobroma grandiflorum - Sterculiaceae), marupá (Simaruba amara - Simaroubaceae) and rubber tree (Hevea brasiliensis - Euphorbiaceae), were analyzed by HT-HRGC and HT-HRGC-MS. Esters of homologous series of fatty acids and long chain alcohols, phytol, amyrines and tocopherols were characterized. The characterization of the compounds was based mainly in mass spectra data and in addition by usual spectrometric data (¹H and 13C NMR, IR).

Determinação de corantes artificiais por cromatografia líquida de alta eficiência (CLAE) em pó para gelatina

Synthetic dyes were determined by high performance liquid chromatography in 76 samples of regular jelly and diet jelly powders, of several flavors produced by seven different manufacturers. Three sample of each product, from different batches, were analyzed. The same qualitative composition was observed for products of the same flavor from different manufacturers, but the quantitative composition varied markedly from one manufacturer to the other. There were no or few significant differences between batches from a given manufacturer, demonstrating good quality control in the use of these additives by the food industry. None of the samples exceeded the limit stipulated by Brazilian legislation.

Estudo da estrutura e da solvatação do HNP-3, um antibiótico natural, por dinâmica molecular

The structure and hydration of the HNP-3 have been derived from molecular dynamics data using root mean square deviation, radial and energy distributions. Three antiparallel beta sheets were found to be preserved. 15 intramolecular hydrogen bonds were identified together with 36 hydrogen bonds on the backbone and 35 on the side chain atoms. From the point of view of the hydration dynamics, the analysis shows a high solvent accessibility of the monomer and attractive interactions with water molecules.

Análise química quantitativa para a padronização do óleo de copaíba por cromatografia em fase gasosa de alta resolução

Quantitative GC-FID was evaluated for analysis of methylated copaiba oils, using trans-(-)-caryophyllene or methyl copalate as external standards. Analytical curves showed good linearity and reproducibility in terms of correlation coefficients (0.9992 and 0.996, respectively) and relative standard deviation (< 3%). Quantification of sesquiterpenes and diterpenic acids were performed with each standard, separately. When compared with the integrator response normalization, the standardization was statistically similar for the case of methyl copalate, but the response of trans-(-)-caryophyllene was statistically (P < 0.05) different. This method showed to be suitable for classification and quality control of commercial samples of the oils.

Novas fases estacionárias à base de sílica para cromatografia líquida de alta eficiência

The present work reviews recent advances in the preparation of new reversed phase packing materials such as sterically protected, bidentate, hybrid organic-inorganic and monolithic phases and phases containing embedded polar groups. The bonding chemistry involved in the preparation of these phases as well as their advantages over conventional C8 and C18 reversed phases are discussed. Understanding the reasons behind the development of these newer column packings helps analysts select the best stationary phase for a given application.