Search results for " ACE"
showing 10 items of 1883 documents
Determination of organochlorine pesticide residues in honey from the central zone of Portugal and the Valencian community of Spain
2004
In this study nine organochlorine pesticide residues ([alpha]-, [beta]-, and [gamma]-hexachlorocyclohexane (HCH), hexachlorobenzene (HCB), aldrin, p,p'-DDE, p,p'-DDD, o,p'-DDT, and p,p'-DDT) in forty nine samples of honey collected from markets of Portugal and Spain during 2001 and 2002, respectively, were evaluated. For this evaluation, three analytical procedures were studied. The analytical procedure, based on LLE extraction with ethyl acetate followed by gas chromatography-electron-capture detection (GC-ECD) for quantification, and mass spectrometry (GC-MS) for confirmation, has been selected. Recoveries of spiked samples ranged from 68%, for [beta]-HCH, and 126% for p,p'-DDT, for forti…
Gel chromatography
1968
Abstract The separation efficiency of gel chromatographic columns was investigated under a wide variety of experimental conditions. By use of reduced quantities it is possible to describe the separation efficiency for different gels and experimental conditions by a single equation. Deviations from this equation were found to be caused by an alteration of the diffusion coefficient within the gel with respect to the mobile phase. Factors governing the gel chromatography of p -oligophenylenes on poly(vinyl acetate) and poly(styrene) gels are generalized and discussed.
Solid-Phase Extraction Techniques for Assay of Diuretics in Human Urine Samples
1991
Abstract Solid-phase extraction techniques were evaluated for the treatment of urine samples in the analysis of diuretics before injection into an HP-Hypersyl ODS-C18 column. Six different reversed-phase extraction columns were tested, and the results obtained are compared with those obtained in a classical liquid-liquid extraction with ethyl acetate. The solid-phase extraction procedures are the best overall choice for all the diuretics tested, due to their versatility, the minor time-consuming, and the good recovery percentages obtained. C18 and C8 packings give the highest recoveries for a majority of the diuretics studied. However, CH or PH columns, due to their greater selectivity, can…
Simultaneous isolation of xanthomegnin, viomellein, rubrosulphin, viopurpurin, and brevianamide A by preparative HPLC.
1984
A method for the isolation of xanthomegnin, viomellein, rubrosulphin, viopurpurin, and brevianamide A from Penicillium viridicatum (DSM 2447) is described. After extraction, HPLC was performed with a preparative silicagel column, eluted with toluene / ethyl acetate / formic acid (27/9/1, v/v/v) and dichloromethane / acetic acid (9/1, v/v). The toxins were detected with a UV-monitor. It was possible to isolate them in an absolutely pure state. The described method is operationally simple and very efficient.
Rayleigh and Brillouin scattering in a lysozyme–water mixture: An unusual behavior around 343K
2011
Abstract This article describes Rayleigh and Brillouin light scattering studies on a lysozyme–water mixture from 293 K to 355 K. The scattering intensities from this system are compared with those from a sodium acetate buffer used to dissolve the lysozyme. It is found that in the vicinity of 343 K the lysozyme–water mixture becomes opalescent, and the intensity of the Brillouin peaks decreases and almost vanishes, to be restored at temperatures above 343 K. Around the same temperature the intensity of the central, unshifted Rayleigh peak, however, increases strongly. No such behavior was observed for the sodium acetate buffer. The analysis of the experimental data indicates an irreversible …
Determination of triazines and organophosphorus pesticides in water samples using solid-phase extraction.
1991
Abstract Octadecyl (C 18 )-bonded porous silica was evaluated for the extraction of triazine and organophosphorus pesticides from natural water. The extraction results showed an effective performance when 1 l of water was passed through small glass columns containing 500 mg of 50–100-μm C 18 bonded porous silica. The absorbed compounds were removed with ethyl acetate, evaporated to 200 μl and determined by gas chromatography. The overall average recoveries were greater than 85% except for dimethoate and trichlorfon. Application of this procedure to the analysis of natural water samples gave results that agree well with those obtained by solvent extraction methods.
Isobaric Vapor–Liquid–Liquid Equilibria for the Ternary Systems Ethanol + Water + Propyl Acetate and 1-Propanol + Water + Propyl acetate
2014
In order to break azeotropes appearing in mixtures of water and either ethanol or 1-propanol, an azeotropic distillation process is proposed using propyl acetate as entrainer. Therefore, isobaric vapor–liquid–liquid equilibrium (VLLE) data at atmospheric pressure have been obtained for the ternary systems ethanol + water + propyl acetate and 1-propanol + water + propyl acetate. Data correlation has been carried out in four different ways and a comparison between the results obtained in each correlation has been done. The set of parameters obtained from the best correlation has been used in the VLLE estimation. Effects of using propyl acetate as entrainer in the azeotropic distillation have …
Chromium(VI) oxide oxidation of non-ethoxylated and ethoxylated alcohols for determination by electrospray ionization mass spectrometry
2010
A new derivatization procedure to increase the sensitivity of electrospray ionization mass spectrometry (ESI-MS) to non-ethoxylated and ethoxylated alcohols was investigated. The analytes were oxidized with chromium(VI) oxide and the resulting carboxylic and ethoxy-carboxylic acids were isolated by extraction with ethyl acetate; the extracts were alkalinized and infused into the ESI-MS system working in the negative-ion mode. The yields of the combined oxidation-extraction were ca. 100% for non-ethoxylated fatty alcohols dissolved in acetone and they decreased moderately in samples containing increasing amounts of water (e.g., a 75% yield was obtained with 50% water). Ethoxylated alcohols w…
Isobaric Vapor−Liquid Equilibria for Water + Acetic Acid + Lithium Acetate
2001
Isobaric vapor−liquid equilibria for all of the binary and ternary mixtures of water, acetic acid, and lithium acetate have been measured at 100.00 kPa using a recirculating still. To take into account the association of the acetic acid in the vapor phase, Marek's chemical theory has been considered. The three experimental binary data sets have been independently correlated using Mock's electrolyte NRTL model, and the binary parameters estimated for each binary system have been used to predict the ternary vapor−liquid equilibrium using the same model. No ternary parameters were required. The ternary equilibrium values obtained in this way agreed well with the experimental values.
Comparison of microextraction procedures to determine pesticides in oranges by liquid chromatography-mass spectrometry.
2002
A liquid chromatographic-mass spectrometric method has been developed for the determination of bitertanol, carbendazim, fenthion, flusilazole, hexythiazox, imidacloprid, methidathion, methiocarb, pyriproxyfen and trichlorfon. Two procedures, based on stir bar sorptive extraction (SBSE) and matrix solid-phase dispersion (MSPD), have been evaluated for the extraction of these compounds in oranges. Their respective advantages and disadvantages are also discussed. The recoveries obtained by MSPD ranged from 47 to 96% and the relative standard deviations (RSDs) ranged from 1 to 15%, whereas with the SBSE method the recoveries were between 8 and 84% and the RSDs between 4 and 16%. Although, the l…