The physical adsorption of a polymer, poly(3,3,3-trifluoropropylmethylsiloxane), on aluminized silica particles, without any additional procedure for polymer immobilization, was studied for 180 days to evaluate the new chromatographic support. Morphological, structural, and chromatographic evaluations of the stationary phase were assessed. After the 15th day of adsorption, a sufficient polymer amount adsorbs onto the aluminized silica particles to separate mixtures of compounds in reversed-phase mode. However, after the 60th day, the polymer layer adhesion occurs more strongly, self-coating the aluminized silica particles. The self-coated stationary phases after 60 days showed similar chromatographic profiles with low hydrophobicity and more interactions with polar compounds, characteristics arising from the fluorinated polymer. The aluminized silica support firmly adhered to the polymer layer, resulting in a separation material chemically stable at alkaline conditions, suggesting a surface reactivity like other well-established supports without asymmetrical peaks for polar compounds.

Poly(ethylene oxide-co-dimethylsiloxane) was thermally immobilized on silica particles-Si(PEO)-to separate small polar compounds with water-rich mobile phases. Poly(ethylene oxide-co-dimethylsiloxane) content on Si(PEO) stationary phase was optimized using a central composite design. Infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis morphologically and structurally characterized the optimized material. Separation of standard test mixtures showed that the Si(PEO) phase had a typical reversed-phase elution order. However, the Si(PEO) phase retained polar compounds better than C18 or aqueous C18 phases under water-rich mobile phases. Under this condition, small changes in the acetonitrile fraction resulted in a marked increase in the retention of some polar drugs on the Si(PEO) phase. A typical condition observed in per aqueous liquid chromatography separations, a more environmentally friendly liquid chromatography approach. On the other hand, hydrophobic compounds showed lower mass transfer rates due to their low solubility in the aqueous mobile phase. Thus, the Si(PEO) phase was more suitable and efficient for separating polar or hydrophilic compounds.

Biodiesel purification by water washing has been proved to be an unattractive process from an economic and environmental point of view. In this work, we propose the use of regenerated cellulose membranes from peanut shell as an alternative in the biodiesel purification. The preparation of the membranes was optimized from a central composite design, resulting in dense and non-porous membranes. However, in contact with biodiesel, the membranes undergo expansion due to the retention of methanol, water, and glycerol molecules, allowing the permeation of fatty acid methyl esters. The filtered biodiesel presents quality parameters, such as total ester content of 98.3 ± 1.4% and free glycerol content < 0.02%, in agreement with the main regulatory agencies. The regenerated cellulose membranes from peanut shell are easily prepared, with high repeatability (relative standard deviation (RSD) < 1.8%) and are presented as an economical and environmental solution for the biodiesel purification.

Excessive use of pesticides can lead to the accumulation of residues in different parts of plants, endangering various species and contaminating foods. Honey can be used as an indicator of agricultural contamination and pre-mature bee mortality by pesticides. However, to quantify pesticide residues in honey, high sensitivity analytical methodologies are required. In this work, a new method was proposed for the determination of seven pesticides, widely used in Triângulo Mineiro, in honey samples based on QuEChERS method and quantification by UHPLC-MS/MS. The method was optimized and validated according to the protocol recommended by the European Community. The method presented LOQ in the range of 0.6-4.0 µg kg-1, lower than the MRLs established for the pesticides studied. Also, the methodology showed high accuracy, with recoveries ranging from 89-107%, and good accuracy, RSD <14%. Honey samples obtained in the Triângulo Mineiro region and subjected to the determination of pesticide residues were analyzed by the analytical methodology, indicating the presence of methomyl and imidacloprid residues in all samples. These results indicate that beehives close to the grain and sugarcane crops are being affected by the application of pesticides in the Triângulo Mineiro Region, Brazil.

Buffered solutions, additives, and column temperature are widely used in high-performance liquid chromatography to promote adequate retention of compounds and to improve the chromatographic separation. However, these factors can dramatically reduce the column lifetime. In this work, the effect of column temperature, pH and the salt type and concentration in buffered mobile phases were evaluated on the stability of a typical commercial C18 stationary phase. A method for rapid evaluation of stationary phase degradation caused by these variables was employed to avoid the generation of large volumes of organic waste. By monitoring the performance of stationary phase in the separation of a standard test mixture, it was possible to verify that the pH of the mobile phase is the most drastic condition to reduce the column lifetime. Buffer solutions of inorganic salts as well as the use of temperatures above 40 °C also significantly reduce the column lifetime. However, a column can have its use extended working with low concentrations of organic additives in the mobile phase, under moderated temperature, and adjusting the pH to the safety range of silica-based materials.

This study describes the use of uncured polydimethylsiloxane (PDMS) as a binder agent to prepare carbon paste electrodes (CPEs). A comparative study between the properties of CPEs prepared with PDMS and mineral oil Nujol®, the most common binder agent for CPEs, was carried out. Cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry showed that PDMS-CPEs presented higher electrical conductivity, active electrochemical area, and wider useful potential window compared with Nujol®-CPEs. Moreover, PDMS-CPEs were more stable in aqueous mixtures containing 50% (v/v) of ethanol or methanol than Nujol®-CPEs. PDMS-CPEs have also provided higher sensitivity and lower limit of detection to propranolol than Nujol®-CPE. Therefore, this study demonstrated that PDMS is a promising alternative binder agent able to produce CPEs with superior chemical/electrochemical stability and improved analytical performance.

Solid phase extraction (SPE) is one of the main sample preparation techniques. However, the cost of cartridges and the strong retention of hydrophobic compounds in traditional solid phases are limiting factors for their use. This paper describes the application of lab-made SPE cartridges with low retention material as solid phase, Si(PDAS) - poly(dimethyl-co-alkylmethylsiloxane) thermally immobilized on silica, in the determination of pesticide residues in surface water samples. The extraction method of three pesticides: carbendazim, diurom and methyl parathion in water samples was developed, optimized and validated using Si(PDAS) cartridges and HPLC-UV for quantification. The optimized method required a small organic solvent volume for the elution of pesticides from Si(PDAS), producing a concentration factor of 1000 times and allowing limits of detection like those obtained with hyphenated techniques. The validated method for extraction of pesticides in water samples presented: accuracy, with pesticide recoveries between 70-110%; precision, with RSD < 20%, and; high detectability, resulting in LOQ < 0.4 µg L-1 for all compounds. Si(PDAS) cartridges showed similar efficiency to those commercial C18 for the extraction of pesticides in surface water samples, with additional advantages such as ease, simplicity and low cost of preparation, up to six times cheaper than commercial cartridges.

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 phases.

C18 chemically bonded sorbents have been the main materials used in solid phase extraction (SPE). However, due their high hydrophobicity some hydrophobic solutes are strongly retained leading to the consumption of larger quantities of organic solvent for efficient recoveries. This work presents a sorbent with lower hydrophobicity but similar selectivity to the C18 sorbent, prepared by thermal immobilization of poly(dimethylsiloxane-co-alkylmethylsiloxane) (PDAS) on silica. PDAS has organic chains with methyl groups alternating with octadecyl or hexadecyl groups in its monomeric unities. For the Si(PDAS) sorbent presented, the polymeric layer was physically adsorbed on the silica surface with 12% carbon load. Although the coating of silica with the polymeric layer was incomplete, the PDAS provided better protection for the silica surface groups, promoting mostly hydrophobic interactions between analytes and the sorbent. Sorption isotherm studies revealed that the retention of hydrophobic solutes on Si(PDAS) was less intense than on conventional sorbents, confirming the lower hydrophobicity of the lab-made sorbent. Additional advantages of Si(PDAS) include simplicity and low cost of preparation, making this material a potential sorbent for the analysis of highly hydrophobic solutes.

A porfirina 5,10,15,20-Tetra(4-piridil)manganês(III), [Mn-TPyP(H2O)2]PF6, e a porfirina supramolecular eletropolimerizável (ESP), {Mn-TPyP(H2O)2[RuCl3(dppb)]4}PF6 (dppb = 1,4-bis(difenilfosfina)butano), foram sintetizadas e caracterizadas. Um filme fino da PSE foi obtido na superfície do eletrodo de carbono vítreo utilizando o método de voltametria cíclica. Foi observado um aumento da corrente de pico com o aumento do número de ciclos voltamétricos, mostrando um comportamento típico de espécies sendo adsorvidas na superfície do eletrodo. O eletrodo modificado com a ESP foi utilizado para a quantificação de acetoaminofeno por voltametria cíclica. O eletrodo modificado apresentou resposta linear de corrente de pico anódico em função da concentração de acetoaminofeno na faixa de concentração entre 0,05 e 0,70 mmol L- 1. O eletrodo modificado foi utilizado para a determinação de acetoaminofeno em uma amostra comercial e os resultados foram satisfatórios, pois apresentaram concordância quando comparado pelo método de HPLC.

Porphyrin 5,10,15,20-Tetra(4-pyridyl)manganese(III), [Mn-TPyP(H2O)2]PF6, and electropolymerized supramolecular porphyrins (ESP), {Mn-TPyP(H2O)2[RuCl3(dppb)]4}PF6 (dppb = 1,4-bis(diphenilphosphine)butane), were synthesized and characterized. A thin solid film of ESP was obtained on a glass carbon electrode surface by a cyclic voltammetry method. The peak current increased with the number of voltammetric cycles, which shows a typical behavior of the species being adsorbed on the surface of the electrode. Cyclic voltammetry was also employed for acetaminophen quantification using an ESP modified electrode. The modified electrode shows a linear relationship between the anodic peak current and the concentration of acetaminophen (in the rage 0.05 to 0.7 mmol L- 1). The performance of the modified electrode was verified by the determination of acetaminophen in a commercial pharmaceutical product and the results were in good agreement with those obtained by a control HPLC method.

Uma nova fase estacionária baseada na imobilização térmica do poli(metiltetradecilsiloxano) (PMTDS) sobre partículas de sílica recoberta com mistura de zircônia e titânia foi preparada e avaliada pela separação cromatográfica de misturas testes neste trabalho. As partículas esféricas foram caracterizadas por análise elementar, MEV, infravermelho e 29Si RMN. As propriedades físico-químicas da fase PMTDS com suporte misto se apresentaram intermediárias às de fases PMTDS baseadas em sílica titanizada e sílica zirconizada. O desempenho cromatográfico da fase Si-Zr/Ti(PMTDS) foi similar ao desempenho de fases contendo apenas um dos óxidos metálicos no suporte, a preparação da fase permitiu a observação do efeito de cada óxido no processo de separação e estabilidade da fase Si-Zr/Ti(PMTDS). A estabilidade hidrolítica da fase Si-Zr/Ti(PMTDS) foi similar a de fases PMTDS com suporte de sílica titanizada, e duas vezes mais estáveis que fases PMTDS com suporte de sílica.

A new stationary phase based on the thermal immobilization of poly(methyltetradecylsiloxane) (PMTDS) on silica particles coated with a mixture of zirconia and titania was prepared and evaluated for the chromatographic separation of test mixtures. The spherical particles were characterized by elemental analysis, SEM, FTIR and 29Si NMR. The physicochemical properties of PMTDS phase supported on Si-Zr/Ti were intermediate between PMTDS phases supported on titanized silica and zirconized silica. The chromatographic performance of Si-Zr/Ti(PMTDS) phase was similar to PMTDS phases based on metal oxide coated silica having only one metal oxide and the preparation of a Si-Zr/Ti(PMTDS) phase allowed evaluation of the effect of each oxide, zirconia and titania, on the separation process and on the stability of the immobilized polymer phase. The hydrolytic stability of Si-Zr/Ti(PMTDS) stationary phase was similar to the Si-Ti(PMTDS) phase, improving the chemical stability of the silica-based PMTDS phase by about 100%.

O aumento da estabilidade química e a redução da alta atividade de grupos residuais têm sido, nas últimas quatro décadas, os principais focos de pesquisas na preparação de fases estacionárias para cromatografia líquida de alta eficiência na modalidade de fase reversa (CLAE-FR). Novas e eficientes estratégias de modificação da superfície da sílica e a introdução de novos materiais como suportes cromatográficos têm minimizado estas limitações e possibilitado uma crescente popularização da CLAE-FR. Neste trabalho será apresentada uma visão geral do estado da arte de uma das estratégias de preparo de fases estacionárias que vem contornando tais limitações da CLAE-FR; as fases estacionárias baseadas na imobilização de polímeros orgânicos pré-sintetizados sobre partículas de sílica e sílica metalizada (zirconizada e titanizada). Uma consideração especial será dada ao desenvolvimento destas fases estacionárias ocorrido no Brasil nos últimos 15 anos.

Increasing stability and reducing the high activity of residual groups from stationary phases have been the main focuses of research on the preparation of reversed-phase high-performance liquid chromatography (RP-HPLC) phases over the last four decades. New and more efficient strategies for modifying the silica surface as well as the introduction of new chromatographic supports have minimized these effects and have enabled the increasing popularization of RP-HPLC. In this paper, an overview will be given of the state-of-the-art in stationary phases for RP-HPLC based on immobilization of pre-synthesized organic polymers on both silica and metalized-silica supports. Special consideration is given to the development of HPLC stationary phases in Brazil in the past 15 years.

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.

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.

This paper presents a simple and practical thermogravimetric method for determining the layer thickness of immobilized polymer stationary phases used in reversed-phase high-performance liquid chromatography. In this method, the weight loss of different polysiloxanes immobilized onto chromatographic supports, determined over the temperature range 150-650 ºC, demonstrated excellent agreement with the sum of carbon and hydrogen content obtained by elemental analysis. The results presented here suggest that the thermogravimetric procedure is an accurate and precise method to determine the polymeric material content on polymer-coated stationary phases.

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.