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Z El Rassi

Publications and source records attributed to Z El Rassi.

33 records · Page 2Linked to original sources
PubMed1999

Recent developments in capillary electrophoresis and capillary electrochromatography of carbohydrate species.

This review article is concerned with the recent developments in capillary electrophoresis (CE) and capillary electrochromatography (CEC) of carbohydrates. The literature shows that CE possesses impressive potential in the analysis of carbohydrates. On the other hand, CEC has just started to show promise in the analysis of carbohydrates. Advances in separation and detection approaches of derivatized and underivatized carbohydrates are discussed based on the available literature. In addition, important applications are illustrated.

Carbohydrates↗
PubMed1999

Capillary electrophoresis of glucosinolates and their degradation products.

Glucosinolates are important natural products occurring mainly in plants of the Cruciferae family. This review article is aimed at describing the recent progress made in capillary electrophoresis of glucosinolates and their degradation products. It describes the various electrophoretic systems and detection schemes introduced to date for the capillary electrophoresis (CE) of glucosinolates and their degradation products. Also included in this review are the applications of CE to the qualitative and quantitative determination of glucosinolates and their degradation products in plant extracts.

Electrophoresis, Capillary↗
PubMed1999

Capillary electrophoresis and electrochromatography of pesticides and metabolites.

Synthetic pesticides are important chemicals since they are widely used to control many types of weeds, insects and other pests in a wide variety of agricultural and nonagricultural settings. This review article is aimed at describing the recent progress made in capillary electrophoresis (CE) and capillary electrochromatography (CEC) of pesticides and their metabolites. The various electrophoretic systems and detection schemes that have been introduced so far for the CE and CEC of pesticides are discussed. Also included in this review article are the various approaches for trace enrichment that are involved in the analysis of dilute pesticide samples.

Chromatography↗
PubMed1999

High-performance liquid phase separation of glycosides. 5. Determination of individual glucosinolates in cabbage and rapeseed by laser-induced fluorescene capillary electrophoresis via the enzymatically released isothiocyanate aglycon.

A capillary electrophoresis (CE) method was developed for the profiling and determination of individual glucosinolates (GSs) via their isothiocyanate degradation products upon myrosinase digestion. The resulting isothiocyanates, the structures of which are reflective of the parent GS's, were then converted to their corresponding amines via base hydrolysis or reaction with 1, 2-benzenedithiol. Subsequently, the amines were fluorescently labeled to allow their sensitive detection by laser-induced fluorescence (LIF). The CE method involved the use of in situ charged micelles for the separation of isothiocyanates and their corresponding fluorescently labeled amines by micellar electrokinetic capillary chromatography (MECC). The term "in situ charged micelles" refers to micelles formed by complexing the polar hydroxyl groups of glycosidic surfactants with borate. The MECC method with on-column LIF detection was applied to the determination of GSs in white cabbage, rapeseed leaves, and rapeseed roots.

Brassica↗
PubMed1998

Capillary electrochromatography of derivatized mono- and oligosaccharides.

An octadecyl-silica (ODS) stationary phase with light surface coverage of octadecyl ligands was introduced for capillary electrochromatography (CEC) at moderate electroosmotic flow (EOF) velocity. The ODS stationary phase was intentionally produced with light surface coverage in order to ensure a moderate EOF velocity across the packed capillary column, thus allowing relatively rapid analysis time. Despite the fact that the stationary phase leaves 75% of the surface silanols unreacted, fused-silica capillary columns packed with this ODS stationary phase exhibited reversed-phase behavior toward neutral alkylbenzene homologous solutes using hydroorganic eluents. Closely related p-nitrophenylglycosides including some p-nitrophenyl-monosaccharides and p-nitrophenyl-maltooligosaccharides were readily separated on the ODS capillary column within a relatively short analysis time. Also, alpha- and beta-anomers of some p-nitrophenyl-monosaccharides were readily separated in the presence of a small amount of borate buffer in the hydroorganic eluent.

Acetonitriles↗
PubMed1998

Capillary electrochromatography with novel stationary phases. I. Preparation and characterization of octadecylsulfonated silica.

A novel silica-based stationary phase was developed for use in capillary electrochromatography (CEC) at relatively high electroosmotic flow (EOF). The silica was first bonded with a relatively hydrophilic layer bearing strong sulfonic acid groups. To this charged polar sublayer, octadecyl functions were covalently attached to yield the nonpolar top layer. This novel stationary phase, referred to as octadecylsulfonated silica (ODSS), was packed in bare fused-silica capillaries or in capillaries with the same coating as the sublayer on the silica-based stationary phase. The resulting packed columns were evaluated in CEC using alkylbenzenes as the test model solutes. Good separations can be achieved in less than 8 min, much faster than when using a regular octadecyl silica capillary column. Due to the permanent negative charge provided by the sulfonated sublayer on both the capillary walls and the silica particles, the magnitude of the EOF remained more or less constant over a wide range of pH, and its magnitude can be conveniently varied by the applied voltage.

Benzene↗
PubMed1998

Capillary zone electrophoresis of proteins with fused-silica capillaries having polymers and surfactants adsorbed onto surfactant moieties previously covalently bound to the capillary column surface.

Fused-silica capillary columns having cationic surfactant moieties (CSM) covalently attached to the capillary inner walls were introduced for the separation of proteins by capillary zone electrophoresis (CZE). The CSM capillary coating proved to be useful in the separation of basic and acidic proteins when modified hydroxypropylcellulose (HPC), namely epoxybutane-HPC (EBHPC), was adsorbed to the primary CSM coating, yielding a hybrid coating (i.e., coating consisting of a covalently bound ligand and an adsorbed ligand). The EBHPC layer rendered the capillary surface highly hydrophilic, thus permitting the separation of basic proteins with relatively high plate counts. Also, the CSM coating was useful for the separation of acidic proteins when the capillary wall had, in addition, a negatively charged polymer adsorbed to the surface, e.g., hyaluronic acid. In general, neutral and charged polymeric compounds could be readily adsorbed by the CSM coating, thus altering the zeta potential of the capillary and diminishing solute adsorption to the capillary surface. In other words, the sign of the zeta potential of the capillary surface could be tailored to be of the same sign as the charge of the analytes. Under these conditions, little or no solute-wall interaction could be observed due to electrostatic repulsion. Although the capillary surface was charged, the presence of adsorbed polymer suppressed or, in most cases, even eliminated the electroosmotic flow (EOF).

Adsorption↗
PubMed1998

Necrolytic migratory erythema, first symptom of a malignant glucagonoma: treatment by long-acting somatostatin and surgical resection. Report of three cases.

We report three cases of malignant glucagonoma with necrolytic migratory erythema as the first clinical symptom. Long-acting somatostatin analogue was the first step of a multimodal therapeutic strategy which included surgical resection of the primary tumour in every case. Liver metastases which were present in two patients were treated by hepatic arterial chemoembolization and systemic chemotherapy in one case and by liver resection for cytoreduction and hepatic arterial chemoembolization in another case. Skin lesions resolved in all three patients.

Aged↗
PubMed1997

Comparison of alkylglycoside surfactants in enantioseparation by capillary electrophoresis.

Three alkylglycoside surfactants, namely n-octyl-beta-D-glucopyranoside (OG), n-nonyl-beta-D-glucopyranoside (NG), and n-octyl-beta-D-maltopyranoside (OM), were compared in the enantiomeric separation of dansyl amino acids, binaphthyl phosphate, bupivacaine and warfarin. While only OM exhibited an enantioselectivity toward warfarin, bupivacaine, and dansyl tryptophan, all three surfactants were effective in the enantiomeric resolution of napthyl phosphate and other dansyl amino acids. With the exception of naphthyl phosphate, which could be resolved enantiomerically with OM at surfactant concentrations below the CMC, all solutes required surfactant concentrations greater than the CMC value. This was attributed to the strong hydrophobic association of napthyl phosphate with the OM monomers and to the presence of maltoside residue in the OM surfactant. In general, the optimum surfactant concentration needed for maximum enantiomeric resolution was an inverse function of the hydrophobic character of the solute. Under a given set of conditions, the enantiomeric resolution exhibited by the alkylglycoside surfactants was largely influenced by the extent and loci of solute solubilization into the micelle, and by the nature of the chiral sugar head group of the surfactant.

Amino Acids↗
PubMed1997

Capillary electrophoresis of pesticides: V. Analysis of pyrethroid insecticides via their hydrolysis products labeled with a fluorescing and UV absorbing tag for laser-induced fluorescence and UV detection.

Some representative standard pyrethroid insecticides, namely permethrin, phenotrin, cypermethrin, sanmarton and fenpropathrin, were subjected to base hydrolysis with the aim of facilitating the indirect determination of these neutral species of low water solubilities by aqueous capillary electrophoresis. This first involved the base fragmentation of the pyrethroids in alcohol buffer (pH 12.0), and then the selective tagging of the carboxylated hydrolytic products with 7-aminonaphthalene-1,3-disulfonic acid (ANDSA) via a condensation reaction in the presence of organic soluble carbodiimide. The tagging of the hydrolytic products with ANDSA imparted each of the derivatives with two strong sulfonic acid groups whose permanent charges were necessary for achieving aqueous capillary electrophoresis. In addition, the labeling with ANDSA allowed the detection of the derivatives at low levels by capillary electrophoresis laser-induced fluorescence. The geometric and optical isomers of the ANDSA derivatives of the pyrethroid hydrolytic products were best separated when using electrolyte systems composed of sodium phosphate buffer, pH 6.5, containing n-octylglucoside chiral surfactant in the presence of small amounts of acetonitrile (e.g., 10% v/v).

Electrophoresis, Capillary↗
PubMed1997

Recent developments in capillary electrophoresis of carbohydrate species.

Carbohydrates are ubiquitous species involved in many life processes. Because of the multilateral roles of carbohydrates, their analysis has come to have increasing importance. As shown in this review, capillary electrophoresis in its various modes of operation has proved very useful in the analysis of carbohydrate species including mono- and oligosaccharides, glycoproteins, glycopeptides and glycosaminoglycans. Advances in separation approaches and applications as well as advances in detection including sensitive and selective pre-column derivatization are described. In summary, this comprehensive review is a supplement to previous reviews and covers the published work in 1996 and the first half of 1997.

Carbohydrates↗
PubMed1997

Capillary electrophoresis of pesticides.

Pesticides are important and diverse environmental and agricultural species. Their determination in pesticide formulations, in feed and food, and in complex environmental matrices (e.g., water, soil, sludge, sediments, etc.) often requires separation methods of high efficiency, unique selectivity and high sensitivity. As shown in this comprehensive review, capillary electrophoresis meets these requirements and has proved to be a suitable microseparation technique for the analysis of a wide variety of chiral and achiral pesticides. It is also shown that by combining selective precolumn derivatization schemes, sensitive detection methods (e.g., laser induced fluorescence detection) and trace enrichment techniques, capillary electrophoresis (CE) is capable of determining pesticides at trace levels as those usually encountered in environmental samples.

Electrophoresis, Capillary↗
PubMed1995

Capillary enzymophoresis of nucleic acid fragments using coupled capillary electrophoresis and capillary enzyme microreactors having surface-immobilized RNA-modifying enzymes.

This report describes the coupling of capillary enzyme reactors to capillary electrophoresis, which is termed capillary enzymophoresis. In the present study, the capillary enzyme reactors were prepared by immobilizing RNA-modifying enzymes, e.g., RNAse T1 and RNAse U2, on the inner walls of 50 microns fused-silica capillaries. These microreactors served to selectively modify the solutes (or substrates) before entering the separation capillary. Capillary enzymophoresis using single or mixed enzyme reactors proved useful in identifying minute amounts of dinucleotides as well as the fingerprinting of tRNAs. The immobilized RNase T1 and RNase U2 displayed their usual enzymic activities toward RNA fragments and in addition exhibited different activity-pH dependency than the soluble enzymes. This was attributed to microenvironmental effects arising from the charged nature of the capillary walls in the close proximity of the immobilized enzymes. The enzyme reactors were reusable for several RNA samples and showed chemical and thermal stability.

Electrophoresis, Capillary↗
PubMed1991

High-performance reversed-phase chromatographic mapping of 2-pyridylamino derivatives of xyloglucan oligosaccharides.

Xyloglucan oligosaccharides from cotton cell walls and tamarind seeds were derivatized with 2-aminopyridine and subsequently separated by reversed-phase chromatography (r.p.c.) using an octadecylsilyl silica stationary phase and aqueous-organic eluents with 0.01% (v/v) trifluoroacetic acid. The chromatographic behavior of the 2-pyridylamino derivatives of xyloglucan oligosaccharides was examined under a wide range of elution conditions, including gradient steepness and shape, initial acetonitrile concentration in the eluent, and pore size of the r.p.c. packings. Relatively steep acetonitrile gradients resulted in poor resolution of the different xyloglucan fragments, which is believed to be the result of acetonitrile-induced conformational changes. Under these circumstances the elution order of the derivatized xyloglucan oligosaccharides was such that the smaller fragments eluted from the column before the larger ones. R.p.c. packing with a 70-A pore size necessitated relatively high acetonitrile concentration in the eluent when compared with 300-A stationary phase. The r.p.c. mapping of 2-pyridylamino derivatives of xyloglucan oligosaccharides was best achieved when both a wide-pore octadecyl-silyl silica stationary phase and a shallow gradient with consecutive linear segments of increasing acetonitrile concentration in the eluent were employed. This combination yielded rapid r.p.c. maps of the xyloglucan fragments from different sources with high separation efficiencies and concomitantly high resolution. The effects of the nature of the sugar residues in the xyloglucan oligomers and their degree of branching on r.p.c. retention and selectivity are also highlighted.

Aminopyridines↗