Search results for " Extraction"
showing 10 items of 1344 documents
Solid phase extraction of amines
2005
Abstract The objective of this paper is to provide information about solid phase extraction (SPE) as an alternative to liquid–liquid extraction of amines from several matrices. Different sorbents ranging from non-polar phases, such as C 18 silica to more polar such as cyanopropylsilica (CN) have been tested for analysis of aliphatic amines as monoamines, diamines and polyamines. Phenylalkylamines such as amphetamine or methamphetamine and heterocyclic amines such as histamine or cephalosporins (which also contain a carboxylic group), have also been studied. The different steps involved in the extraction procedure have been tested (conditioning, retention, pre-concentration, washing and elut…
Determination of theophylline and paraxanthine in urine samples by liquid chromatography using the H-point standard additions method
1992
Abstract The simultaneous determination of theophylline and paraxanthine in urine samples by the H-point standard additions method (HPSAM) is described. Samples are extracted with C 18 solid-phase extraction cartridges and chromatographed using a Hypersil C 18 -ODS column and a mobile phase consisting of acetonirile-phosphate buffer in the gradient elution mode. Under these conditions theophylline and paraxanthine are eluted with short retention times. Although their chromatographic peaks are overlapped and their spectra are very similar, the H-point standard additions method provides excellent results in the determination of both xanthines at therapeutic levels.
Solid-phase extraction of quaternary ammonium herbicides
2000
This paper highlights recent advances in the solid-phase extraction (SPE) of quaternary ammonium herbicides in water, soil, plant and biological samples. After a brief introduction summarizing the properties of quaternary ammonium herbicides and the difficulties involved in measuring them, attention is paid primarily to solid supports used for isolation and concentration, pre-treatments required for the different matrices, and eluents applied for quantitative desorption of these analytes. The determination techniques used after SPE and applications of the proposed SPE methodology are also briefly discussed.
High-pressure solubility data of system ethanol (1)+catechin (2)+CO2 (3)
2001
Abstract Supercritical fluid extraction posses several advantages over traditional liquid–solvent-based extraction methods including improved selectivity, expeditiousness, automation and environmental safety. Fluid phase equilibrium data is essential for study the viability of supercritical extraction and the design of the extraction columns often used for this type of separations. During the past few years it has been demonstrated that phenolic compounds, such catechins and procyanidins from seeds, contribute to both the flavour properties and the pharmacological effects of wine. The extraction of catechin using supercritical CO2 is not possible, it only extracts traces of product, probabl…
High-pressure solubility data of the system resveratrol (3)+ethanol (2)+CO2 (1)
2001
Abstract Supercritical fluid extraction possesses several advantages over traditional liquid-solvent-based extraction methods, including improved selectivity, expeditiousness, automation and environmental safety. Fluid-phase equilibrium data are essential for studying the viability of supercritical extraction and the design of the extraction columns often used for this type of separation. Resveratrol has been correlated with serum lipid reduction and inhibition of platelet aggregation, and its cancer chemopreventive activity has recently been reported. The extraction of resveratrol using supercritical CO 2 is not possible; it only extracts traces of product, probably due to its polar nature…
Analysis of neuropeptide Y and its metabolites by high-performance liquid chromatography-electrospray ionization mass spectrometry and integrated sam…
2000
A novel restricted access cation exchanger with sulphonic acid groups at the internal surface was proven to be highly suitable in the sample clean up of peptides on-line coupled to HPLC-electrospray ionization (ESI)-MS. Neuropeptide Y (NPY) and several of its fragments in plasma were subjected to the sample clean-up procedure. The peptides were eluted by a step gradient from the restricted access column, applying 10 mM phosphate buffer pH 3.5 from 5 to 20% (v/v) of acetonitrile with 1 M NaCl and transferred to a Micra ODS II column (33x4.6 mm). The separation of the peptides and their fragments was performed by a linear gradient from 20 to 60% (v/v) acetonitrile in water with 0.1% formic ac…
Determination of pyrethroid insecticide residues in vegetable oils by using combined solid-phases extraction and tandem mass spectrometry detection
2005
Abstract A methodology has been developed for the determination of pyrethroid insecticide residues in vegetable oils, based in a solid-phase extraction (SPE) with combined solid supports phases. Several solid phases such as florisil, alumina, C18 and graphitized carbon black were tested in order to minimize fat residues, being a combination of treated alumina and C18 which provided the best results. Oil samples were partitioned with acetonitrile–hexane (1:1) and then eluted through a combined column packed with deactivated basic-alumina and C18, employing the acetonitrile extract as elution solvent. Gas chromatography tandem mass spectrometry was used for determination. Tetramethrin, Bifent…
Sulphonic acid strong cation-exchange restricted access columns in sample cleanup for profiling of endogeneous peptides in multidimensional liquid ch…
2006
Abstract In this work, the pore structural parameters and size exclusion properties of LiChrospher strong cation-exchange and reverse phase restricted access materials (RAM) are analysed. The molecular weight size exclusion limit for polystyrenes was found to be about 17.7 kDa, while for standard proteins, the molecular weight size exclusion limit was higher, at approximately 25 kDa. The average pore diameter on a volume basis calculated from the pore network model changes from 8.5 nm (native LiChrospher) to 8.6 nm (diol derivative) to 8.2 nm (sulphonic acid derivative) to 6.9 nm ( n -octadecyl derivative). Additional characterisations were performed on restricted access materials with nitr…
Pesticides (New Generation) and Related Compounds, Analysis of
2017
Miscellaneous pesticides and related compounds comprise substances that can neither be included in the classical chemical category of pesticides nor classified by their mode of action. They are a heterogeneous group of substances, the most representative of which are macrocyclic lactones, chloronicotinyls, tetranortriterpenoids, ammonium quaternary salts, dinitroanilines, acetamides, oximes, triazoles, and pyridine-based molecules. The pesticides covered in this article have hardly changed in the last years. However, their analytical determination has undergone significant improvements. This article provides a well-defined and critical compilation of the sample treatment and clean-up proced…