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See detailSimultaneous Determination of Methylphenobarbital Enantiomers and Phenobarbital in Human Plasma by on-Line Coupling of an Achiral Precolumn to a Chiral Liquid Chromatographic Column
Ceccato, Attilio ULg; Boulanger, Bruno ULg; Chiap, Patrice ULg et al

in Journal of Chromatography. A (1998), 819(1-2), 143-53

A fully automated liquid chromatographic (LC) method for the simultaneous determination of methylphenobarbital enantiomers and phenobarbital in human plasma has been developed. The method is based on the ... [more ▼]

A fully automated liquid chromatographic (LC) method for the simultaneous determination of methylphenobarbital enantiomers and phenobarbital in human plasma has been developed. The method is based on the use of a precolumn packed with an internal-surface reversed-phase packing material (LiChrospher ADS) for sample clean-up coupled to LC analysis on a cellulose tris(4-methylbenzoate) based chiral stationary phase (Chiralcel OJ-R). A 100-microliter plasma sample was injected directly on the precolumn packed with LiChrospher RP-18 ADS using a mixture of pH 5.0 phosphate buffer-methanol (97:3, v/v) as washing liquid. The analytes were then eluted in the back-flush mode with the LC mobile phase. The enantiomeric separation of methylphenobarbital was achieved on Chiralcel OJ-R). The retention times were modelled using a D-optimal design with ten experimental points in order to optimise the LC mobile phase for the separation of phenobarbital from the enantiomers of mephobarbital. The factors selected were the acetonitrile content, the pH and the sodium perchlorate concentration in the mobile phase. A Derringer's desirability function was used to find an optimal and robust solution within the experimental domain. The mobile phase selected consisted of a mixture of pH 7.0 phosphate buffer-acetonitrile (60:40, v/v). The elution profiles of phenobarbital, methylphenobarbital and blank plasma samples on the precolumn and the time needed for analyte transfer from the precolumn to the analytical column were then determined. Finally, the method developed was validated. [less ▲]

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See detailSupercritical fluid extraction of polychlorinated dibenzo-p-dioxins from fly ash: the importance of fly ash origin and composition on extraction efficiency
Windal, I.; Eppe, Gauthier ULg; Gridelet, A. C. et al

in Journal of Chromatography. A (1998), 819(1-2), 187-195

Supercritical fluid extraction (SFE) of polychlorinated dibenzo-p-dioxins (dioxins) from by ash samples, collected at different municipal waste incinerators, was investigated using supercritical CO2 and ... [more ▼]

Supercritical fluid extraction (SFE) of polychlorinated dibenzo-p-dioxins (dioxins) from by ash samples, collected at different municipal waste incinerators, was investigated using supercritical CO2 and compared to the classical Soxhlet extraction. Results were correlated to fly ash composition, which is strongly related to the fume purification system used in the incinerators. Fly ash collected at the bottom of the electrostatic precipitator is composed of dust coming from the combustion unit, but also of lime and eventually of activated charcoal injected in the fumes for acids and pollutants removal. When only lime is used for the fume purification, SFE of dioxins from fly ash leads to better results than Soxhlet extraction. The use of a binary cosolvent (trifluoroacetic acid in toluene) greatly increases the percentage recovery. When activated charcoal is used in conjunction with lime for the fume purification, SFE under classical extraction conditions is not powerful enough to extract dioxins, which are strongly adsorbed to the residual activated charcoal. (C) 1998 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailAutomated Determination of Verapamil and Norverapamil in Human Plasma with on-Line Coupling of Dialysis to High-Performance Liquid Chromatography and Fluorometric Detection
Ceccato, Attilio ULg; Chiap, Patrice ULg; Hubert, Philippe ULg et al

in Journal of Chromatography. A (1996), 750(1-2), 351-60

A fully automated method for the simultaneous determination of verapamil and its main metabolite norverapamil in human plasma is described. This method is based on on-line sample preparation using ... [more ▼]

A fully automated method for the simultaneous determination of verapamil and its main metabolite norverapamil in human plasma is described. This method is based on on-line sample preparation using dialysis followed by clean-up and enrichment of the dialysate on a precolumn and subsequent HPLC analysis with fluorometric detection. All sample handling operations were performed automatically by a sample processor equipped with a robotic arm (ASTED system). The plasma samples were dialysed on a cellulose acetate membrane (cut-off: 15 kD) and the dialysate was purified and enriched on a short pre-column filled with cyanopropyl silica. Before starting dialysis, this trace enrichment column (TEC) was first conditioned with the HPLC mobile phase and then with pH 3.0 acetate buffer. 370 microliters of plasma sample spiked with the internal standard (gallopamil) were dialysed in the static-pulsed mode. The solution at the donor side was pH 3.0 acetate buffer containing Triton X-100 while the acceptor solution was made of the same acetate buffer. When dialysis was discontinued, the analytes were desorbed from the TEC by the HPLC mobile phase and transferred to the C18 analytical column by means of a switching valve. This mobile phase consisted of a mixture of acetonitrile, pH 3.0 acetate buffer and 2-aminoheptane. The influence of different parameters of the dialysis process on the recovery of verapamil and norverapamil has been studied. The effect of the volume, the aspirating and dispensing flow-rates of the dialysis solution has been investigated. The recoveries of verapamil and norverapamil in plasma were close to 75% and the limits of quantification were 5 ng/ml for both analytes. The method was found to be linear in the concentration range from 5 to 500 ng/ml (r2: 0.9996 for both analytes). The intra-day and inter-day reproducibilities at a concentration of 100 ng/ml were 2.3% and 5.6% for verapamil and 1.7% and 5.1% for norverapamil, respectively. [less ▲]

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See detailMulti-Residue Screening and Confirmatory Analysis of Anabolic Steroids in Urine by Gas Chromatography Coupled with Tandem Mass Spectrometry
Van Vyncht, G.; Gaspar, P.; De Pauw, Edwin ULg et al

in Journal of Chromatography. A (1994), 683(1), 67-74

The diversity of substances used illegally as growth promoters in meat production requires the development of multi-analyte methods of analysis involving a sample pretreatment step that is as rapid and as ... [more ▼]

The diversity of substances used illegally as growth promoters in meat production requires the development of multi-analyte methods of analysis involving a sample pretreatment step that is as rapid and as easy as possible, followed by a specific and sensitive determination of several residues within the same run. A general strategy for the screening and confirmatory analysis of fifteen artificial anabolic compounds in urine samples is described. It is based on solid-phase extraction on C18 Empore discs and amino-bonded columns followed, after derivatization (trimethylsilyl or methyloxime-trimethylsilyl derivatives), by gas chromatography coupled with collisionally activated dissociation tandem mass spectrometry. [less ▲]

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See detailKnowledge-Based System for the Automated Solid-Phase Extraction of Basic Drugs from Plasma Coupled with Their Liquid Chromatographic Determination. Application to the Biodetermination of Beta-Receptor Blocking Agents
Hubert, Philippe ULg; Chiap, Patrice ULg; Moors, M. et al

in Journal of Chromatography. A (1994), 665(1), 87-99

Techniques for the preparation of biological samples are often based nowadays on solid-phase extraction (SPE). The different SPE steps can be performed automatically on disposable extraction cartridges ... [more ▼]

Techniques for the preparation of biological samples are often based nowadays on solid-phase extraction (SPE). The different SPE steps can be performed automatically on disposable extraction cartridges (DECs) by means of a sample processor. A knowledge-based system was developed to facilitate the development of fully automated methods for the solid-phase extraction of relatively hydrophobic basic drugs from plasma, coupled with their determination by high-performance liquid chromatography (HPLC). The DEC filled with 50 mg of cyanopropyl-bonded silica phase is first conditioned with methanol and buffer solution (pH 7.4). After sample application, the DEC sorbent is washed with the same buffer. The analytes are then desorbed with an appropriate eluent and the eluate is finally diluted with the same buffer as used in the HPLC mobile phase before injection. Under these conditions, only three variables are still to be optimized: the composition and volume of the elution solvent and the volume of buffer to be added to the eluate. On the basis of this general strategy, a decision tree providing information about suggested starting conditions and guidelines for the optimization of the three variables was developed and implemented by use of a hypermedia software. This didactic expert system was evaluated using several beta-receptor blocking agents as model compounds and the operating conditions obtained for the automated SPE of these compounds are presented. A method for the determination of propranolol in plasma using the SPE conditions deduced from the knowledge-based system was validated. The absolute recovery of propranolol is ca. 93% and the limit of detection is 1.3 ng ml-1. The mean within-day and between-day reproducibilities are 2.3 and 3.6%, respectively. [less ▲]

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See detailFully Automated Determination of Sulfamethazine in Ovine Plasma Using Solid-Phase Extraction on Disposable Cartridges and Liquid Chromatography
Hubert, Philippe ULg; Chiap, Patrice ULg; Evrard, Brigitte ULg et al

in Journal of Chromatography. A (1993), 622(1), 53-60

An automatic sample preparation procedure followed by on-line injection of the sample extract into a HPLC system has been developed for the quantitative analysis of sulfamethazine and its N4-acetyl ... [more ▼]

An automatic sample preparation procedure followed by on-line injection of the sample extract into a HPLC system has been developed for the quantitative analysis of sulfamethazine and its N4-acetyl metabolite in ovine plasma. The sample clean-up was performed by solid-phase extraction (SPE) on C18 disposable extraction cartridges (DECs). All the sample handling operations were effected by a robotic auto-sampler. The DEC was first conditioned with methanol and phosphate buffer pH 7.4. After loading 1.0 ml of plasma sample onto the DEC, the latter was washed with the same buffer. The elution step was performed with methanol (0.25 ml) and the eluate was then diluted by adding 0.75 ml volume of phosphate buffer pH 6.4. A 20-microliters volume of the resultant solution was injected onto an octadecyl silica column preceded by a short guard column. The HPLC mobile phase was methanol-phosphate buffer pH 6.4 (25:75, v/v). Sulfamethazine and N4-acetylsulfamethazine were determined photometrically at 262 nm. Under these conditions, linear calibration curves ranging from 2 to 250 micrograms ml-1 have been obtained for both compounds. Drug recoveries were higher than 90% and typical relative standard deviation values were 0.7% (within-day) and 2.0% (between-day) at a plasma concentration of 50 micrograms ml-1. [less ▲]

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See detailPurification Of Antifungal Lipopeptides By Reversed-Phase High-Performance Liquid-Chromatography
Razafindralambo, Hary ULg; Paquot, Michel ULg; Hbid, Choukri et al

in Journal of Chromatography. A (1993), 639(1), 81-85

A rapid procedure for the purification of antifungal lipopeptides from Bacillus subtilis, a potential agent for biocontrol of plant diseases, was tested. It consists of a solid-phase extraction on C18 gel ... [more ▼]

A rapid procedure for the purification of antifungal lipopeptides from Bacillus subtilis, a potential agent for biocontrol of plant diseases, was tested. It consists of a solid-phase extraction on C18 gel followed by reversed-phase chromatography using a biocompatible PepRPC HR 515 column with a pharmacia fast protein liquid chromatographic system. This is a very effective method for isolating and fractionating iturin A and surfactin, two lipopeptides of different nature, co-produced by Bacillus subtilis strain S499. The presence of homologous lipopeptides was easily detected. [less ▲]

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See detailApplication of High-Performance Liquid Chromatography to the Study of Thiamine Metabolism and in Particular Thiamine Triphosphatase
Bettendorff, Lucien ULg

in Journal of Chromatography. A (1991), 566(2), 397-408

Thiamine triphosphate can be found in most tissues at very low levels, but its role is unknown. Organs and muscles that generate electrical impulses are particularly rich in this compound. This paper ... [more ▼]

Thiamine triphosphate can be found in most tissues at very low levels, but its role is unknown. Organs and muscles that generate electrical impulses are particularly rich in this compound. This paper describes a thiamine triphosphatase from the electrical organ of Electrophorus electricus. The activity of this enzyme, as measured by a high-performance liquid chromatographic method, is closely anion-regulated. Furthermore, thiamine triphosphate increases chloride uptake in membrane vesicles prepared from rat brain. Our results suggest that this compound could play an important role in the regulation of chloride permeability. [less ▲]

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See detailDosage densitométrique d'hétérosides de la quercetine dans les extraits végétaux
Brasseur, T.; Wauters, J. N.; Angenot, Luc ULg

in Journal of Chromatography. A (1988), 437(1), 260-4

The assay of quercetine glycosides is easy by TLC and gives better results than those analysed by HPLC in the case of the analysis of a mixture of glucosyl-3 - quercetin and Rhamnoglucosyl-3-quercetin ... [more ▼]

The assay of quercetine glycosides is easy by TLC and gives better results than those analysed by HPLC in the case of the analysis of a mixture of glucosyl-3 - quercetin and Rhamnoglucosyl-3-quercetin because these products are better separated by TLC. The spray reagent for detection was the mixture NP/PEG 400 [less ▲]

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See detailDosage de glycérides par densitométrie
Wathelet, Jean-Paul ULg; Claustriaux, Jean-Jacques ULg; Séverin, Michel

in Journal of Chromatography. A (1975), 110

After determination of charring conditions and the measurement by densitometry of lipids separated by thin-layer chromatography, a statistical analysis was performed to determine the significance of the ... [more ▼]

After determination of charring conditions and the measurement by densitometry of lipids separated by thin-layer chromatography, a statistical analysis was performed to determine the significance of the results. Calibration curves were studied and response factors calculated for some saturated and unsaturated triglycerides. [less ▲]

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