2006: Cem anos das palavras cromatografia e cromatograma

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Self-immobilization of poly(methyltetradecylsiloxane) onto metalized silica particles as stationary phases for HPLC

This work presents a study of the sorption of a pre-synthesized polysiloxane, poly(methyltetradecylsiloxane) - PMTDS, onto zirconized and titanized-silica particles that results in efficient stationary phases for reversed phase liquid chromatography. The sorbed materials, after 6 days at room temperature without any chemical or physical agent, denominated as self-immobilized stationary phase, present appropriate polymeric layer thicknesses that cover the metalized silica surfaces. The self-immobilization of polymer onto titanized silica particles produces more homogeneous polymeric coatings and stationary phases without silanophilic activity. Zirconized silica-based phases were more chemically resistant, despite their strong retention of basic solutes. In general, the chromatographic performance and chemical stability of metalized silica-based self-immobilized PMTDS phases were similar to conventional chemically bonded stationary phases27712971304CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPSem informaçãoSem informaçã

The search for more pH stable stationary phases for high performance liquid chromatography

High performance liquid chromatographic (HPLC) separations are largely carried out using reversed phase conditions with stationary phases based on silica. A serious problem with these stationary phases is the tendency of silica to dissolve in high pH solutions often needed to separate basic compounds. The literature reports many different ways that have been tried to resolve this problem. This paper reports the results obtained in our laboratory with stationary phases prepared using silica supports having a layer of a metal oxide (zirconia or titania) attached on their surfaces, followed by immobilization of a polysiloxane or by organofunctionalization with a trimethoxyalkylsilane. Stability tests, also developed in our laboratory, indicate that the metal oxide layer increases the HPLC column lifetimes by making the stationary phase less susceptible to dissolution.As separações por cromatografia líquida de alta eficiência (CLAE) são realizadas, na maioria das vezes, em condições de fase reversa empregando fases estacionárias a base de sílica. Um problema sério com estas fases reversas é a tendência da sílica dissolver em soluções de pH elevado, frequentemente necessárias para separar compostos básicos. A literatura reporta várias maneiras diferentes de tentar solucionar este problema. Este artigo relata os resultados obtidos com fases estacionárias desenvolvidas no nosso laboratório, utilizando suportes de sílica, contendo uma camada de um óxido metálico (zircônia ou titânia) ligada à sua superfície, seguido por imobilização de um polissiloxano ou por organofuncionalização com um trimetóxialquilsilano. Testes de estabilidade, também desenvolvidos no nosso laboratório, indicaram que a camada de óxido metálico aumenta o tempo de vida da coluna cromatográfica, por tornar a fase estacionária menos susceptível à dissolução.60461

Controlling factors determining the selective HSCN addition to double bonds and their application to the synthesis of 7-isothiocyano-7,8-alpha-dihydro-bisabolene

The reactivity of terminal and trisubstituted double bonds of monoterpenes with HSCN has been examined by GC giving evidence that kinetics is responsible for the chemoselective addition to terminal double bonds in terpenes. The results show that the addition to the terminal double bond is about 17 times faster than for trisubstituted double bonds and that the presence of the first SCN group in the molecule prevents a second addition. The presence of a hydroxyl or methoxy group in the molecule, decreases the reaction kinetics. Based on these kinetic experiments a two steps synthesis of the natural product 7-isothiocyano-7,8-dihydro-alpha-bisabolene using bisabolol as starting material, was planned and successfully accomplished.A reatividade de duplas ligações terminal e trissubstituída de monoterpenos com HSCN foi examinada por CG evidenciando que fatores cinéticos são responsáveis pela adição quimiosseletiva em duplas ligações terminais em terpenos. O resultado mostra que a adição é cerca de 17 vezes mais rápida em duplas terminais do que em duplas trissubstituídas e que a presença do primeiro grupo SCN impede a entrada de um segundo grupo. A presença de um grupo hidroxila ou metoxila na molécula diminui sensivelmente a velocidade da reação. A partir do estudo acima foi possível elaborar e realizar a síntese do produto natural 7-isothiocyano-7,8-dihydro-alfa-bisabolene em duas etapas a partir do bisabolol.661666Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

The challenges of the analysis of basic solutes by reversed phase liquid chromatography: some possible approaches for improved separations

This review considers some of the difficulties encountered with the analysis of basic solutes using reversed-phase chromatography, such as detrimental interaction with stationary phase silanol groups. Methods of overcoming these problems in reversed-phase separations, by judicious selection of the stationary phase and mobile phase conditions, are discussed. Developments to improve the chemical and thermal stability of stationary phases are also reviewed. It is shown that substantial progress has been made in the manufacturing of stationary phases, enabling their use over a wide variety of experimental conditions. In addition, general measures to significantly extend their lifespan are discussed.9931003Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Applications of high performance liquid chromatography for the study of emerging organic pollutants

Emerging organic pollutants (EOP) include many environmental contaminants based on commercial products such as pharmaceuticals, personal care products, detergents, gasoline, polymers, etc. EOP may be candidates for future regulation as they offer potential risk to environmental and human health due to their continual entrance into the environment and to the fact that even the most modern wastewater treatment plants are not able to totally transform / remove these compounds. High performance liquid chromatography is recommended to separate emerging organic pollutants with characteristics of high polarity and low volatility, especially pharmaceuticals, from environmental matrices.665676Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Aplicações de cromatografia líquida de alta eficiência para o estudo de poluentes orgânicos emergentes

Emerging organic pollutants (EOP) include many environmental contaminants based on commercial products such as pharmaceuticals, personal care products, detergents, gasoline, polymers, etc. EOP may be candidates for future regulation as they offer potential risk to environmental and human health due to their continual entrance into the environment and to the fact that even the most modern wastewater treatment plants are not able to totally transform / remove these compounds. High performance liquid chromatography is recommended to separate emerging organic pollutants with characteristics of high polarity and low volatility, especially pharmaceuticals, from environmental matrices

Stationary phases for reversed phase high performance liquid chromatography (RP-HPLC) based on functionalized inorganic oxide surfaces

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.61662

Preparation, characterization and application of C8 type stationary phases modified by metallic oxides for liquid chromatography

This work describes three C8-stationary phases for high performance liquid chromatography based on silica metallized with ZrO2, TiO2 or Al2O3 layers, having poly(methyloctylsiloxane) immobilized onto their surfaces. The stationary phases were characterized using XRF, XAS, FTIR, SEM and elemental analysis to determine the physical characteristics of the oxide and polysiloxane layers formed on the surfaces and chromatographically to evaluate the separation parameters. The results show the changes on the silica surface and allowed proposing a structure for the oxide layer, being observed tetrahedral and octahedral structures, what is completely new in the literature. The formation of a homogeneous layer of metallic oxide (TiO2 and ZrO2) was observed on the silica. The C8-titanized and C8-aluminized stationary phases presented good chromatographic performances, with good values of asymmetry and efficiency. All stationary phase presented few loss of the polymeric layer after the HPLC, indicating that this layer is well attached on the metalized support.11311138Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP