Search results for " Phase"

Off-line dansylation of amines using C18 solid-phase packings: study of the fluorescence and chemiluminescence detection by post-column derivatizatio…

1999

Abstract Dansylation of amines (primaries and secondaries) using C18 solid-phase supports is described. The time of analysis and the handing sample have been markedly improved with respect to those required for solution dansylation. The dansylated amine derivates were injected onto the liquid chromatography system and fluorescence detected. The sensitivity and selectivity is better than the other dansylation procedures described in the literature and also better than other derivatization reagents such 1,2-napthoquinone 4-sulfonate (NQS) or 3,5-dinitrobenzoyl chloride (3,5-DNB). Dansyl compounds can also form chemiluminescent derivatives, therefore a post-column derivatization procedure with…

BEHAVIOUR OF GRAPHITIZED CARBON BLACK IN THE EXTRACTION OF POLAR NON-IONIC NITROGEN-CONTAINING PESTICIDES. A CHECKING OF HYPOTHESES

2000

Graphitized Carbon Black (GCB) extractive cartridges are evaluated for on-line coupling with a C8 analytical column to determine eleven carbamates and one carboximide pesticide from spiked deionized water at the 1.2 μg/L level. Several experiments were carried out to ascertain whether GCB saturation, pesticide degradation on the surface, existence of by-pass channels, mobility among the bulk cartridge, or strong retention on the surface interfere with the determination of pesticides. Problems in on-line CGB elution are partially solved by modifying the acetonitrile/water gradient to contain a front of 100% acetonitrile for a few seconds. Eluting the same GCB cartridges off-line with dichlor…

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…

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.

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…

HERBICIDES | Solid-Phase Extraction

2000

Pleurotus ostreatus volatile aroma compounds identified from fruit-body and from mycelium grown in submerged and solid-state cultures

2003

Comparative analyses of volatile aroma compounds of the Pleurotus ostreatus JMO.95 fruit-body and its corresponding mycelium grown in liquid, on agar surface, or on solid support cultures have been carried out by dynamic headspace concentration using GC/MS and GC/sniffing. The aroma of the fruit-body was due essentially to the presence of octan-3-one and, in a lesser extent, to the presence of octan-3-ol. Other compounds, such as oct-l-en-3-ol, oct-l-en, 2-methylbutanol and a-pinene were also present in low concentrations. The comparison of the aromatic spectra of the fruit-body with the aromatic spectra of mycelia obtained under different culture conditions indicated that the main aromatic…