Estudo ab-initio da a-alanina em meio aquoso

Ab initio Hartree-Fock (HF), Density Functional (B3LYP) and electron correlation (MP2) methods have been used to caracterize the aqueous medium intramolecular hydrogen bond in a-alanine. The 6-31G* and 6-31++G** were taken from Gaussian94 library. We were concerned on the structure of three conformers of a-alanine, in their neutral form plus on the structure of the zwitterionic form (Z). The Z structure is a stationary point at the HF/6-31G* level but it is not when diffuse functions and electron correlation are included. This results shows that the Z form does not exist in the gas phase. The inclusion of solvent effects changed significantly the results obtained in gas phase, therefore this inclusion make the Z form a stationary point within all level of theory, and the relative energy depends dramatically on the level of calculation.

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.

Extração em fase sólida (SPE) e micro extração em fase sólida (SPME) de piretróides em água

The pyrethroids bifenthrin, permethrin, cypermethrin and deltamethrin were extracted by solid phase extraction (SPE) and solid phase microextraction (SPME). The analysis were performed on a gas chromatograph with electron capture detection (GC-ECD). Octadecil Silano-C18, Florisil and Silica stationary phases were studied for SPE. Better results were obtained for Florisil which gave recoveries from 80% to 108%. Pyrethroids extraction by SPME showed a linear response and a detection limit of 10 pg ml-1. Although the data showed that the two extraction methods were able to isolate the pesticide residues from water samples, the best results were obtained by using SPME which is more sensitive, faster, cheeper, being a more useful technique for the analysis of pyrethroids in drinking water.

Estudo de compostos orgânicos em lixiviado de aterros sanitários por EFS e CG/EM

The main purpose of this work was the qualitative study of organic compounds in landfill leachate. The samples were collected from a sanitary landfill located at Gravataí, a southern Brazilian city, that receive both, industrial and domestic refuse. The samples were submitted to solid phase extraction (SPE) with XAD-4 resin as the stationary phase. The instrumental analysis was performed by Gas Chromatography with a Mass Spectrometry Detector (GC/MSD). The compounds achieved in the SPE extracts were tentatively identified by the GC/MS library. It was found several oxygen and nitrogen compounds like carboxylic acids, ketones, amines and amides. Sulfur compounds and phthalate esters are also identified.

Células a combustível de baixa potência para aplicações estacionárias

A paradigmatic shift in developing fuel cell for stationary applications has been occurring in the last ten years. Previously, 100 kW class to a few MW class power plants were preferred but recently, the development has drifted towards units of only a few kW. The motivation is the present market situation, which favors disperse residential electric power generation from natural or liquefied gas. Membrane-type fuel cells are very promising for this application, due to their present state of development in the automobile industry. More recently, small ceramic fuel cells (SOFC) has also been found to be adequate for this application. Considering a family of 4 members, 1 kW (electric) units seem to be optimal for individual residences. This presentation discusses briefly the Brazilian scenario with respect to these units.

Xerogel p-anisidinapropilsílica: estudo da estabilidade térmica e da resistência à lixiviação com solventes

The xerogel p-anisidinepropylsilica was obtained. This solid presents some residual paraffin and also a small fraction of high organofunctionalized material that was leached in polar solvent. The xerogel purification could be achieved by exhaustively washing with hexane and dichloromethane solvents, or submitting the xerogel to thermal treatment up to 300 ºC, in vacuum. The resulting purified xerogel material present an appreciable thermal stability and resistance to leaching by solvents.

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.

Pré-concentração de nitrosaminas a partir de amostras aquosas por extração em fase sólida e cromatografia capilar eletrocinética micelar

This paper describes the development of a methodology for solid phase extraction (SPE) and pre-concentration of nitrosamines from aqueous samples using granular activated charcoal as stationary phase. micelar electrokinetic capillary Chromatography (MEKC) was used for the separation and identification of the nitrosamines in the extracts. Using a sample with 50 µg l-1 of each nitrosamines standards (dimethylnitrosamine, DMN; diethylnitrosamine, DEN; N-nitrosopyrrolidine, NPYR; N-nitrosopiperidine, NPIP; N-nitrosomorpholine, NMOR), the methodology showed a range of recuperation from 29 to 107% with a linear zone between 10 and 500 µg l-1. The developed methodology can be applicable to the determination of these analytes in different aqueous samples.

Quantificação do linalol no óleo essencial da Aniba duckei Korstermans utilizando uma nova coluna capilar POLYH4-MD em Cromatografia Gasosa

In the present work a polyurethane polymer derived from castor oil was used as stationary phase for capillary gas chromatography. The polymer was obtained by reaction of hydroxylated compound and isocynate (NCO), forming urethane. Columns of 7 m x 0,25 mm were then coated with this stationary phase (film thickness of 0,25 µm) using static coating method. The Grob test was also performed. Samples of essential oil of the Aniba duckei Korstermans was then analysed in POLYH4-MD capillary column in order to evaluate its chromatographic perfomance. The linalool was found to be the major component and has been used as compound of departure for many important syntheses. Results show that the experimental columns give higher resolution and can be employed for analysis of essentials oils.

Quantitative analysis of phenol and alkylphenols in Brazilian coal tar

The main purpose of this work is the identification and quantification of phenolic compounds in coal tar samples from a ceramics factory in Cocal (SC), Brazil. The samples were subjected to preparative scale liquid chromatography, using Amberlyst A-27TM ion-exchange resin as stationary phase. The fractions obtained were classified as "acids" and "BN" (bases and neutrals). The identification and quantification of phenols, in the acid fraction, was made by gas chromatography coupled to mass spectrometry (GC/MS). Nearly twenty-five phenols were identified in the samples and nine of them were also quantified. The results showed that coal tar has large quantities of phenolic compounds of industrial interest.

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.

Análise enantiosseletiva de fármacos: contribuições da cromatografia líquida de alta eficiência e eletroforese capilar

The demand for analytical methods suitable for accurate and reproducible determination of drug enantiomers has increased significantly in the last years. High-performance liquid chromatography (HPLC) using chiral stationary phases and capillary electrophoresis (CE) are the most important techniques used for this purpose. In this paper, the fundamental aspects of chiral separations using both techniques are presented. Some important aspects for the development of enantioselective methods, particularly for the analysis of drugs and metabolites in biological samples, are also discussed.

Análise de fármacos em material biológico: acoplamento microextração em fase sólida "no tubo" e cromatografia líquida de alta eficiência

A new solid phase microextraction (SPME) system, known as in-tube SPME, was recently developed using an open tubular fused-silica capilary column, instead of an SPME fiber, as the SPME device. On-line in-tube SPME is usually used in combination with high performance liquid chromatography. Drugs in biological samples are directly extracted and concentrated in the stationary phase of capillary columns by repeated draw/eject cycles of sample solution, and then directly transferred to the liquid chromatographic column. In-tube SPME is suitable for automation. Automated sample handling procedures not only shorten the total analysis time, but also usually provide better accuracy and precision relative to manual techniques. In-tube SPME has been demonstrated to be a very effective and highly sensitive technique to determine drugs in biological samples for various purposes such as therapeutic drug monitoring, clinical toxicology, bioavailability and pharmacokinetics.

Fases estacionárias monolíticas para separações cromatográficas

Monolithic stationary phases represent a new generation of chromatographic separation media. These phases consist of a continuous separation bed prepared by in situ polymerization or consolidation inside the column tubing. In recent years, their simple preparation procedure, unique properties and excellent performance have attracted quite remarkable attention in liquid chromatography and capillary electrochromatography. This review summarizes the preparation, characterization and applications of monolithic stationary phases. The analytical potential of these columns is demonstrated with separations involving various families of compounds in different separation modes.

Cromatografia em leito móvel simulado na produção de substâncias enantiomericamente puras ou enriquecidas em larga escala

There is great interest nowadays in the use of preparative liquid chromatography as an effective tool for the production of enantiomerically pure, or enriched, compounds for the pharmaceutical industry. To make the chromatographic process economically attractive, attention is now focused on the choice of the chromatographic operating mode to minimize eluent consumption and to maximize productivity. Among the alternatives to the traditional batch chromatography, attention is now shifting towards simulated moving bed (SMB) technologies and a review covering the latest developments in this area seems timely. Several aspects of this important analytical technique are presented and details concerning the SMB technology for process optimization are outlined.