Critical evaluation of microextraction pretreatment techniques-Part 2: Membrane-supported and homogenous phase based techniques.

This review follows up on Part 1, which focused on classification and evaluation of single drop and sorbent-based microextraction techniques. Membrane- and homogenous phase-based microextraction techniques are discussed and classified in Part 2. These techniques are more recent than those in Part 1 and considerable attention has been paid to their development. The new methodologies are more sensitive and, thanks to their miniaturization, they can be classified as "green", but no exhaustive classification is available. We hope that this review will contribute to better orientation in these methods.

Critical evaluation of microextraction pretreatment techniques - Part 1: Single drop and sorbent-based techniques.

Sample pretreatment techniques or preconcentration constitute a very important step before the analysis of environmental, clinical, pharmaceutical, and other complex samples. Thanks to extraction techniques it is possible to achieve higher method sensitivities and selectivities. Miniaturization microextraction methods make them more environmentally friendly and only small amounts of samples are required. In the past 30 years, a number of microextraction methods have been developed and used and are documented in thousands of articles. Many reviews have been written focusing on their use in specified professional fields or on the latest trends. Unfortunately, no uniform nomenclature has been introduced for these methods. Therefore, this review attempts to classify all the essential microextraction techniques and describes their advantages, disadvantages, and the latest innovations. The methods are divided into two main groups: single drop and sorbent-based techniques according to the type of extraction phase.

Analysis of estrogens and estrogen mimics in edible matrices--a review.

This review provides a brief survey of the biological effects of selected endocrine-disrupting compounds that are formed after internal exposure of organisms. Further, the present analytical methods available for the determination of these compounds in foodstuffs are critically evaluated. The attention is primarily devoted to the methods for sample pretreatment, which are the main source of errors and are usually the most time-consuming step of the whole analysis. This review is focused on selected natural and synthetic estrogens, estrogen conjugates, and chemical additives used in the plastic industry that can act as estrogen mimics.

Analysis for estrogens as environmental pollutants--a review.

The approaches to the analysis for estrogen compounds as environmental pollutants are critically reviewed and evaluated on the basis of significant, recent original publications. The importance of sample pretreatment and analyte preconcentration techniques is pointed out, with an emphasis on SPE and on the use of highly selective interactions such as molecular recognition. The hyphenated systems of high-performance gas or liquid chromatography and mass spectrometric techniques are discussed as the basic methods of determination of estrogens in environmental samples. Immunochemical procedures are shown to be useful in semiquantitative screening of estrogen pollutants (e.g. ELISA kits). Classical HPLC and GC with common UV/Vis, fluorescence and electrochemical detection are useful in routine checking on higher pollutant concentrations.

Gas chromatography/mass spectrometry of oils and oil binders in paintings.

A GC/MS procedure has been developed, optimized, and applied to characterization of oil binders in paintings. The procedure involves hydrolysis of lipids to fatty acids (FAs) and derivatization of FAs to fatty acid methyl esters (FAMEs) by a solution of sodium methanolate in methanol at an elevated temperature. FAMEs are analyzed by temperature-programed GC followed by full-scan MS. Old and dried samples are subjected to extraction of nonpolymerized FAMEs into dichloromethane prior to hydrolysis. The method provides a good repeatability of results and has been applied to the characterization of common plant oils used in paintings, to commercial oil and tempera paints, to model painting samples, and to samples taken from real paintings. The fresh oils and binders can readily be identified and characterized. The ratio of the methyl esters of palmitic and stearic acids can be used to characterize oil binders in old works of art.

An evaluation of the experimental approaches to detection of small ions in CE.

This review points out some important trends in the development of the detection techniques for small ions in CE. On the basis of selected literature references it briefly discusses some general requirements on detection techniques in CE. Various optical measurements, mass spectrometric approaches and electrochemical detection techniques are dealt with. Some specific features of microchip CE separation and detection are pointed out and possibilities of dual detection are mentioned. The principal parameters of the above detection techniques are then briefly compared.

Characterization of substituted polyacetylene microstructure by pyrolysis gas chromatography.

A series of substituted acetylenes has been polymerized with WOC14/Ph4Sn metathesis catalyst and [Rh(cod)OMe]2 insertion catalyst, and the thermal degradation of the polyacetylenes prepared has been studied using pyrolysis capillary gas chromatography (Py-GC) with flame ionization and mass spectrometric detection to obtain information on the effect of the catalyst on the head-tail (H-T) isomerism of polyacetylenes (poly(phenylacetylene), poly[(4-methylphenyl)acetylene], poly(benzylacetylene), poly((2-fluorophenyl)acetylene], poly[(3-fluorophenyl)acetylene], and poly[(4-fluoro-phenyl)acetylenel). Cyclotrimers have been found to be the main pyrolysis products in all cases. Direct Py-MS connection was used to determine the temperature profiles of the released pyrolysis products. 1,3,5-Trisubstituted benzenes were found to be the predominant pyrolysis products of the polymers prepared with the insertion catalyst, which proves the presence of long head-to-tail sequences of monomeric units in these polyacetylenes. On the other hand, both 1,2,4- and 1,3,5-trisubstituted benzenes are present in significant amounts in the pyrolysis products of polymers prepared with the metathesis catalyst, which proves the presence of a significant content of the head-to-head (HH) and tail-to-tail (TT) linkages in these isomers of polyacetylenes. Contents of the regular (HT) and inverse (HH-TT) monomer linkages (RML and IML, respectively) in polymer chains were determined from the relative amounts of di-, tri-, and tetrasubstituted benzenes found in the Py-GC products.

Porous polyacrylamide monoliths in hydrophilic interaction capillary electrochromatography of oligosaccharides.

Capillary electrochromatography (CEC) of oligosaccharides in porous polyacrylamide monoliths has been explored. While it is possible to alter separation capacity for various compounds by copolymerization of suitable separation ligands in the polymerization backbone, "blank" acrylamide matrix is also capable of sufficient resolution of oligosaccharides in the hydrophilic interaction mode. The "blank" acrylamide network, formed with a more rigid crosslinker, provides maximum efficiency for separations (routinely up to 350,000 theoretical plates/m for fluorescently-labeled oligosaccharides). These columns yield a high spatial resolution of the branched glycan isomers and large column permeabilities. From the structural point of view, some voids are observable in the monoliths at the mesoporous range (mean pore radius ca. 35 nm, surface area of 74 m2/g), as measured by intrusion porosimetry in the dry state.

Affinity liquid chromatography and capillary electrophoresis of seminal plasma proteins.

Interactions of boar, bull, and human seminal plasma proteins with heparin and phosphorylcholine were studied by affinity LC using heparin immobilized to a Toyopearl support. A step gradient elution from 0.15 to 1.50 M NaCl was employed to elute the seminal plasma proteins. Relative amounts of the heparin-binding fraction of seminal plasma proteins (H+) in seminal plasma of three species were determined. Further on, the fraction of seminal plasma proteins interacting with phosphorylcholine-binding proteins (P+) was evaluated. P+ proteins were not found in human seminal plasma and their highest amount was present in bull seminal plasma. A CE method was developed for separation of seminal plasma proteins. Various capillaries and separation conditions were tested; the best resolution was obtained in a bare-silica capillary, with a micellar system consisting of a 0.02 M borate buffer and 0.05 M SDS pH 10.0. The optimized conditions were applied to the identification of the components in boar plasma.

Monolithic organic polymeric columns for capillary liquid chromatography and electrochromatography.

This review briefly summarizes the present state of the preparation and use of capillary monolithic columns for liquid chromatography (LC) and electrochromatography (EC). Most important approaches to the preparation of monolithic stationary phases based on organic polymers are outlined and the properties of the monoliths obtained are compared with those of classical particulate phases. A few selected applications of monolithic columns are shown to demonstrate the most important advantages of monolithic capillary columns. It is concluded that both the monolithic and particulate capillary columns are important and that judicious choice of the type suitable for a particular application requires careful consideration of the purpose of the separation and the properties of the solutes to be separated. Monolithic columns are substantially younger than packed ones and thus will require further theoretical and experimental study to further improve their preparation and to enable reliable prediction of their properties and applicability; nevertheless, they are very promising for the future.