Novos sorventes baseados em poli (metiloctilsiloxano) sobre sílica para uso em extração em fase sólida

This paper presents an easy and practical procedure to obtain silica-based C-8 type sorbents for use in solid-phase extraction. The materials are prepared by depositing poly(methyloctylsiloxane), PMOS, on the silica support. Two different treatments for immobilization were used: thermal treatment or gamma irradiation. Suitable recoveries were obtained after pre-concentration of dilute solutions, at the ng/L level, of a mixture of pesticides, indicating the good performance of the materials.

Utilização da extração em fase sólida (SPE) na determinação de hidrocarbonetos policíclicos aromáticos em matrizes aquosas ambientais

Polycyclic aromatic hydrocarbons (PAHs) are a great environmental concern mainly because of their toxic, mutagenic and carcinogenic potential. This paper reports utilization of the solid-phase extraction (SPE) technique to determine PAHs in environmental aqueous matrices. The recovery from environmental aqueous matrices fortified with PAHs varied from 63.7 to 93.1% for atmospheric liquid precipitation, from 38.3 to 95.1% for superficial river water, and from 71.0 to 95.5% for marine water. No negative matrix effect was observed for the recovery of PAHs from atmospheric liquid precipitation and marine water, but was observed for superficial river water, particularly for PAHs possessing 5 and 6 aromatic rings.

Determinação do coeficiente de atividade na diluição infinita (g¥) através da micro-extração em fase sólida (SPME)

In this study a new approach, solid phase micro extraction (SPME), is used in the evaluation of the infinite dilution activity coefficient of the solute in a given solvent. It is the purpose of the current work to demonstrate a different approach to obtain the data needed for studying the solution thermodynamics of binary liquid mixtures as well as for designing multi-component separations. The solutes investigated at the temperature 298.15 K were toluene, ethyl benzene and xylene in the solvent methanol.

Um espalhador de baixo custo de fase estacionária em placas para cromatografia em camada delgada

Chromatography is a means of separating mixtures into their several components. TLC, mainly a liquid/solid process, is one of the separation techniques most often used. It is indispensable in laboratories dealing with natural products, organic and analytical chemistry. Commercial chromatography plates are offered at relatively high cost. In this work the construction of a hand-operated plate coater of stationary phases of low cost and good reproducibility is described to be used in teaching laboratories and research.

Un método de bajo costo para la determinación de cobre a nivel de vestigios en matrices de interés ambiental por espectrofotometría en fase sólida (EFS)

A method for determining copper by solid phase spectrophotometry (SPS) was optimized using the Doehlert design. Copper(II) was sorbed on a styrene-divinylbenzene anion-exchange resin as a Cu(II)-1-(2-pyridylazo)-2-naphthol (PAN) complex, at pH 7.0. Resin phase absorbances at 560 and 800 nm were measured directly. The detection limit was found to be 2.5 µg L-1. The relative standard deviation on ten replicate determinations of 10 µg Cu(II) in 1000 mL samples was 1.1%. The linear range of the determination was 5.0-100 µg L-1. The method was applied successfully to the determination of Cu(II) in natural water and vegetable samples.

Microextração em fase líquida (LPME): fundamentos da técnica e aplicações na análise de fármacos em fluidos biológicos

The analysis of drugs and metabolites in biological fluids usually requires extraction procedures to achieve sample clean-up and analyte preconcentration. Commonly, extraction procedures are performed using liquid-liquid extraction or solid-phase extraction. Nevertheless, these extraction techniques are considered to be time-consuming and require a large amount of organic solvents. On this basis, microextraction techniques have been developed. Among them, liquid-phase microextraction has been standing out. This review describes the liquid-phase microextraction technique based on hollow fibers as a novel and promising alternative in sample preparation prior to chromatographic or electrophoretic analysis. The basic concepts related to this technique and its applicability in extraction of drugs are discussed.

Determinação de metil-etil-cetona em amostras de urina com amostragem por micro extração em fase sólida (MEFS) em headspace associada à cromatografia gasosa com detector de ionização de chama (CG-DIC)

Methyl ethyl ketone (MEK) is a solvent commonly used in chemical, paint and shoe industry. The aim of this study was to develop and validate a method for urinary quantification of MEK, employing headspace solid phase micro extraction sampling (SPME) coupled to gas chromatography with flame ionization detection (GC-FID). The calibration curve (y=4.6851x-0.0011) presented good linearity with r²=0.9993. Accuracy (94-109%), intra-assay precision (4.07-5.91%) and inter-assay precision (3.03-5.62%) were acceptable. The quantification limit was 0.19 mg/L. This low cost method can be used routinely in the biological monitoring of occupational exposure to MEK, according to the requirements of the Brazilian legislation.

Análise de resíduos de agrotóxicos em tomates empregando dispersão da matriz em fase sólida (DMFS) e cromatografia gasosa

This work was aimed on optimization of the matrix solid-phase dispersion (MSPD) technique using gas chromatography for analyzing residues of chlorpyriphos, λ-cyhalothrin, cypermethrin and deltamethrin in tomatoes. The results showed that silica was more efficient for the clean up of extracts, but florisil provided the highest recovery rates. A 2³ complete factorial design was carried out to evaluate the absorbent/sample ratio, presence of co-column (silica) and ultrasonic bath on the extraction rate. The percentage of extraction of the pesticides chlorpyriphos, λ-cyhalothrin, cypermethrin and deltamethrin were 64.7, 88.3, 99.2 and 89.2%, respectively, with relative standard deviations below 5%.

Estudo por espectroscopia micro-Raman dos mecanismos de separação de fase em vidros fosfatos de metais de transição

Glass-ceramics are prepared by controlled separation of crystal phases in glasses, leading to uniform and dense grain structures. On the other hand, chemical leaching of soluble crystal phases yields porous glass-ceramics with important applications. Here, glass/ceramic interfaces of niobo-, vanado- and titano-phosphate glasses were studied by micro-Raman spectroscopy, whose spatial resolution revealed the multiphase structures. Phase-separation mechanisms were also determined by this technique, revealing that interface composition remained unchanged as the crystallization front advanced for niobo- and vanadophosphate glasses (interface-controlled crystallization). For titanophosphate glasses, phase composition changed continuously with time up to the equilibrium composition, indicating a spinodal-type phase separation.

Determinação de etanol e voláteis relacionados em sangue e fluido oral por microextração em fase sólida em headspace associada à cromatografia gasosa com detector de ionização em chama

The aim of this study was to validate a method for the determination of acethaldehyde, methanol, ethanol, acetone and isopropanol employing solid-phase microextraction associated to gas chromatography with flame ionization detection. The operational conditions of SPME were optimized by response surface analysis. The calibration curves for all compounds were linear with r² > 0.9973. Accuracy (89.1-109.0%), intra-assay precision (1.8-8.5%) and inter-assay precision (2.2-8.2%) were acceptable. The quantification limit was 50 µg/mL. The method was applied to the meaurement of ethanol in blood and oral fluid of a group of volunteers. Oral fluid ethanol concentrations were not directly correlated with blood concentrations.

Enriquecimento de compostos fenólicos de folhas de Inga edulis por extração em fase sólida: quantificação de seus compostos majoritários e avaliação da capacidade antioxidante

A phenolic fraction was obtained from of the acetone-water-acetic acid extract of Inga edulis leaves, by liquid-liquid partition and SPE-C18 cartridges. This method provided an increase of 108, 66, 51, 50 and 36% of flavonols, proanthocyanidins, total polyphenols, gallotannins and flavanols, respectively. The major phenolics in purified fraction were procyanidin B2, catechin and myricetin-3-O-α-L-rhamnopyranoside, which achieved increases of 111, 47 and 45%, respectively, after SPE. Acid hydrolysis confirmed the presence of procyanidins, prodelphinidins and glycosylated flavonoids.

Sistema limpo em linha para extração em fase sólida de contaminantes emergentes em águas naturais

A solid-phase in-line extraction system for water samples containing low levels of emerging contaminants is described. The system was specially developed for large volume samples (up to 4 L) using commercial solid-phase extraction (SPE) cartridges. Four sets containing PTFE-made connectors, brass adapters and ball valves were used to fit SPE cartridges and sample bottles to a 4-port manifold attached to a 20 L carboy. A lab-made vacuum device was connected to the manifold cap. The apparatus is robust and less expensive than the typical available system. Its also provides less experimental handling, avoiding cross contamination and sample losses.

Otimização e validação de métodos analíticos para determinação de BTEX em água utilizando extração por headspace e microextração em fase sólida

Three analytical methods for the determination of BTEX in water were optimized and validated. With the best method the analytes were extracted of 10 mL of sample with 2.50 g of NaCl in headspace vial of 20 mL by HS and SPME to 40 ºC for 30 min for adsorption and to 250 ºC for 4 min for desorption and were analyzed by GC-MS. The recovery was between 97.9% and 104.3%, and the limit of detection was 2.4 ng L-1 for o-xylene. This method was using to analyze BTEX in water supply and surface water in Ouro Preto city. No sample had concentrations of BTEX above the legislation.

Estratégias de pré-concentração em eletroforese capilar: parte 2. Manipulação da velocidade da fase dispersa/secundária

This work describes CE preconcentration strategies based on the effect of manipulation of the disperse/secondary velocity. Introduced by Terabe et al. in 1984, micellar electrokinetic chromatography is a powerful separation approach that increases the usage of electrokinetic phenomena for the separation of nonionic compounds. The main disadvantage of MEKC is the low concentration sensitivity associated with the limited optical path length for on-capillary photometric detection and the limited volume of sample solution that can be injected. This paper compiles on-line concentration strategies for neutral analytes by sample stacking and sweeping in micellar electrokinetic chromatography.

Possibilidades e limitações no uso da temperatura em cromatografia líquida de fase reversa

High-temperature liquid chromatography (HTLC) is a technique that presents a series of advantages in liquid phase separations, such as: reduced analysis time, reduced pressure drop, reduced asymmetry factors, modified retentions, controlled selectivities, better efficiencies and improved detectivities, as well as permitting green chromatography. The practical limitations that relate to instrumentation and to stationary phase instability are being resolved and this technique is now ready to be applied for routine determinations.