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P Sandra

Publications and source records attributed to P Sandra.

At least 37 records · Page 2Linked to original sources
PubMed2001

Capillary zone electrophoresis for the characterization of latex particles.

Capillary zone electrophoresis (CZE) was applied to the separation of acrylic styrene copolymer emulsion particles. Fast separations could be performed on samples containing chemically identical latex particles of different size, as well as on samples with particles of the same size but differing in chemical composition. The developed method was also used for the analysis of water soluble fractions of urethane dispersions. Additionally, the physical interaction between different particles (e.g., acrylic and urethane particles) could be studied using this method. The separation mechanism is based on the zeta potential of the particles and the relaxation effect under the applied analytical conditions.

Acrylates↗
PubMed2001

Recent applications of capillary electrochromatography.

A review is presented of the most important recent applications of capillary electrochromatography (CEC) for the analysis of acidic, basic, and neutral compounds, of biomolecules, environmental substances, natural products, pharmaceuticals, and chiral compounds. Packed-column CEC (packed-CEC), open-tubular (OT-CEC), as well as pressure-assisted CEC (pseudo-CEC) are hereby considered. Papers published between July 1999 and April 2001 were taken into account. Applications before July 1999 have been reviewed in Electrophoresis 1999, 20, 3027-3065.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2000

Automated capillary gas chromatographic system to monitor ethylene emitted from biological materials.

An automated capillary gas chromatographic system to measure ethylene emitted from biological materials is presented. The system consists of an on-line sampling device, a thermodesorption preconcentration apparatus and a capillary gas chromatograph with a flame ionization detection system. The limit of detection achievable on the GC system alone is 5 pg ethylene. The use of the strong Carboxen 1000 adsorbent at a sampling temperature as low as -50 degrees C allows sampling of volumes up to a few liters. Ethylene concentrations at low ppt levels can be accurately and reproducibly determined.

Automation↗
PubMed2000

On the calculation of Gibbs energy corresponding to enantioselective interactions at a direct HRGC separation of enantiomers.

A novel procedure is proposed for the calculation of Gibbs energy corresponding to enantiospecific interactions of 2-(2, 4-dinitrophenoxy)-, 2-phenoxy-, and 2-halogen-n-pentane enantiomers with a beta-cyclodextrin (ChirasilDex) stationary phase under gas chromatographic conditions. This energy is calculated from retention data as a difference between the Gibbs energy of an enantiomer and its corresponding achiral congener. The procedure for the determination of 2-(2,4-dinitrophenoxy)-, 2-phenoxy- and 2-halogen- n-pentane achiral congener retention data is discussed in detail.

Chromatography, Gas↗
PubMed1999

On the performance and inertness of different materials used for the enrichment of sulfur compounds from air and gaseous samples.

The performance of the sorbent polydimethylsiloxane (PDMS) is compared to that of the adsorbents Carbotrap and Tenax for the enrichment of volatile and reactive sulfur compounds. These included: 1- and 2-propanethiol, tetrahydrothiophene, 2-thioethanol and 2-ethylthioethanol. Several artifact-forming reactions were identified on both Tenax and Carbotrap including: H2S elimination and dimerization of thiols. Additionally, permanent adsorption was also observed for heavier solutes. These effects are absent when PDMS is applied. This superior performance is explained by the absence of catalytic or adsorptive activity on PDMS.

Adsorption↗
PubMed1999

Analysis of free fatty acids and fatty acid phenacyl esters in vegetable oils and margarine by capillary electrochromatography.

Capillary electrochromatography (CEC) has been utilized to analyze free fatty acids (FFAs) and fatty acid phenacyl esters (FAPEs) originating from vegetable oils and margarine. The analyses were performed on capillaries 25 and 40 cm long, 100 microm ID, and packed with 3 microm Hypersil ODS. Isocratic elution was achieved with the mobile phase acetonitrile/50 mM 2-(N-morpholino)ethane sulfonic acid (MES), pH 6, at a ratio of 9:1. For quantitative analysis, the formation of FAPE derivatives is preferred. Moreover, the number of double bonds in the FAPEs can be elucidated by measuring the UV absorbance ratio of 240:210 nm. For the determination of the oleate/elaidate ratio in margarines, the FFAs are analyzed because of overlap of elaidate/palmitate in FAPE analysis. Data obtained with CEC and micro liquid chromatography (LC) were compared and CEC was found to be far superior in terms of efficiency and speed of analysis. Important selectivity differences were noted between micro LC on highly endcapped ODS and CEC on the silanol-rich Hypersil ODS.

Chromatography, Liquid↗
PubMed1999

Considerations concerning interaction characterization of oligopeptide mixtures with vancomycin using affinity capillary electrophoresis-electrospray mass spectrometry.

In the past few years affinity capillary electrophoresis (ACE) has proven to be a powerful tool to study molecular interactions. In ACE the change in electrophoretic mobility between a free and a complexed ligand with a receptor dissolved in the background electrolyte is observed. It provides an accurate way to calculate binding or dissociation constants and, when coupled to mass spectrometry, it forms a promising method to analyze solution-based combinatorial libraries. We report a model study on the macrocyclic antibiotic vancomycin using a 36-component library of tetrapeptides of the type 9-fluorenylmethoxycarbonyl (Fmoc)-L-Asp-L-Asp-D-Xaa-D-Xaa. The mass spectrometry conditions were optimized by fine-tuning the background electrolyte and sheath flow composition to achieve optimal sensitivity in the negative ionization mode. Different types of capillaries were also evaluated on their potential to screen combinatorial libraries. The library components that show the strongest interaction were identified. The dissociation constants of a mixture of six compounds with a broad affinity range were simultaneously established by Scatchard analysis on ACE-MS.

Anti-Bacterial Agents↗
PubMed1999

Comparison of highly sulfated alpha-, beta-, and gamma-cyclodextrins and 18-crown-6-tetracarboxylic acid for the enantiomeric separation of some amino acids and derivatives by capillary electrophoresis.

18-Crown-6-tetracarboxylic acid (18C6H4) and highly sulfated cyclodextrins (HS-alpha-, beta-, gamma-CDs) are highly selective chiral selectors for the enantioseparation of solutes bearing the primary amino function. Excellent resolutions were obtained for all solutes on HS-gamma-CD and on 18C6H4. The former, however, is by far the best chiral selector for the solutes studied in this work because the highest resolution is obtained with the shortest migration times. The reversal of the D- and L-migration order on HS-CDs compared to 18C6H4 is an interesting feature for the determination of enantiomeric excess.

Amino Acids↗
PubMed1999

Applications of capillary electrochromatography.

Applications performed by capillary electrochromatography (CEC) in all its modes, namely packed column CEC (packed-CEC), open tubular CEC (OT-CEC) and pressure-assisted CEC (pseudo-CEC), and published by June 1999 are reviewed. The review is divided into (i) separation of neutral, acidic and basic analytes with the main goal of evaluating column and system performance, (ii) separation according to field of application and/or chemical class, and (iii) separation of chiral analytes.

Biological Factors↗
PubMed1998

Determination of phenylurea herbicides in water samples using online sorptive preconcentration and high-performance liquid chromatography with UV or electrospray mass spectrometric detection.

A recently developed method for the extraction of organic micropollutants from aqueous samples based on sorptive enrichment in columns packed with 100% polydimethylsiloxane (PDMS) particles was coupled on-line with HPLC analysis. The sorptive enrichment procedure originally developed for relatively nonpolar analytes was used to preconcentrate polar phenylurea herbicides from aqueous samples. PDMS extraction columns of 5, 10 and 25 cm were used to extract the herbicides from distilled, tap and river water samples. A model that allows prediction of retention and breakthrough volumes is presented. Despite the essentially apolar nature of the PDMS material, it is possible to concentrate sample volumes up to 10 ml on PDMS cartridges without losses of the most polar analyte under investigation, fenuron. For less polar analytes significantly larger sample volumes can be applied. Since standard UV detection does not provide adequate selectivity for river water samples, an electrospray (ES)-MS instrument was used to determine phenylurea herbicides in a water sample from the river Dommel. Methoxuron was present at a level of 80 ng/l. The detection limit of the current set-up, using 10 ml water samples and ES-MS detection is 10 ng/l in river water samples. Strategies for further improvement of the detection limits are identified.

Chromatography, High Pressure Liquid↗
PubMed1998

Capillary electrophoresis and capillary electrophoresis-electrospray-mass spectroscopy for the analysis of heterocyclic amines.

Fourteen heterocyclic amines (HAs) were analyzed by capillary electrophoresis (CE) on a polyvinyl alcohol (PVA)-coated capillary column. The optimized electrolyte is composed of 20 mM ammonium acetate, pH 3.0, and 20% methanol. Similar conditions were applied in electrospray-mass spectrometry (CE-ES-MS). The CE-ES-MS optimization procedure includes the position of the capillary in the stainless steel interface, the flow of the sheath liquid and its composition.

Acetates↗
PubMed1998

Separation of chiral compounds by capillary electrophoresis.

This review presents the different chiral selectors used in capillary electrophoresis (CE) for the separation of enantiomers. The use of charged cyclodextrins, crown ethers, polysaccharides, proteins, natural and synthetic micelles, macrocyclic antibiotics and ergot alkaloids is discussed in detail. Neutral native and derivatized cyclodextrins are not treated because several review articles have already been published on this topic. Recent developments like the application of two chiral selectors in the same background electrolyte are highlighted.

Electrophoresis, Capillary↗
PubMed1998

A sensitive HPLC method for the quantification of free and total p-cresol in patients with chronic renal failure.

Para-cresol (4-methylphenol) is a volatile phenolic compound which is retained in chronic renal failure. Several recent studies suggest that p-cresol interferes with various biochemical and physiological functions at concentrations currently observed in uremia. Only a few methods are available for the determination of p-cresol concentration in serum. In addition, these methods have only been used for the determination of total p-cresol. In particular, the evolution of free (non-protein bound) p-cresol is of concern, because conceivably this is the biologically active fraction. The concentration of free p-cresol, is, however, markedly lower than that of total p-cresol, in view of its important protein binding. We report a method enabling the measurement of total and free p-cresol concentration in serum of healthy controls and uremic patients. Deproteinization, extraction and HPLC procedure are efficient, without interference of other protein bound ligands and/or precursors of p-cresol or phenol. By means of spiking experiments, the measurement of the UV absorbance over the 200-400 nm wavelength range, and capillary gas chromatography-mass spectrometry, the considered compound is identified as p-cresol. With a fluorescence detection at 284/310 nm as extinction/emission wavelengths the detection limit of p-cresol is 1.3 micromol/l (0.14 microg/ml). Recovery of added p-cresol to normal serum is 95.4+/-4.1%. For free p-cresol and total p-cresol determinations, intra-assay and day-to-day variation co-efficients are 3.2%, 4.2%, 6.9% and 7.3%, respectively. Compared to healthy controls, the serum p-cresol levels are 7-10 times higher in continuous ambulatory peritoneal dialysis patients (CAPD), uremic outpatients, and hemodialysis patients: 8.6+/-3.0 vs. 62.0+/-19.5, 87.8+/-31.7 and 88.7+/-49.3 micromol/l (0.93+/-0.32 vs. 6.70+/-2.11, 9.49+/-3.43, and 9.60+/-5.30 microg/ml) (p<0.05), respectively. The difference is even more important if free p-cresol is considered. This corresponds to a decreased protein binding in uremic patients. We conclude that the present method allows an accurate measurement of both total and free p-cresol, and that the measured concentrations in uremia are in the range which may cause biochemical alterations.

Artifacts↗
PubMed1998

Classification of heparinolytic bacteria into a new genus, Pedobacter, comprising four species: Pedobacter heparinus comb. nov., Pedobacter piscium comb. nov., Pedobacter africanus sp. nov. and Pedobacter saltans sp. nov. proposal of the family Sphingobacteriaceae fam. nov.

Sixteen heparinase-producing isolates, related to Sphingobacterium heparinum, were grouped into three major clusters by SDS-PAGE and DNA-rRNA hybridizations. Based on a polyphasic approach, it was shown that isolates of two of these clusters and S. heparinum species belong to a new genus for which the name Pedobacter is proposed. The genus consists of Pedobacter heparinus comb. nov. (formerly Sphingobacterium heparinum), which is the type species, Pedobacter piscium comb. nov. (formerly Sphingobacterium piscium), Pedobacter africanus sp. nov. and Pedobacter saltans sp. nov. and four as-yet-unnamed DNA hybridization groups. All the previously named taxa can be discriminated by phenotypic features, but have strong overall similarities with representatives of the genus Sphingobacterium and the misclassified species [Flexibacter] canadensis. All these organisms constitute a separate rRNA branch in rRNA superfamily V for which the family Sphingobacteriaceae fam. nov. is proposed.

Classification↗
PubMed1997

Micellar electrokinetic chromatography as a fast screening method for the determination of the doping agents furosemide and piretanide in urine.

The possibility of using micellar electrokinetic chromatography for the screening of the loop diuretics piretanide and furosemide in urine was studied. A fast and simple method with good repeatability is described. The method was applied to urine samples collected from a healthy volunteer after oral administration of therapeutic doses of each compound. Positive identification in the urine matrix was possible through recording diode array spectra.

Chromatography, High Pressure Liquid↗
PubMed1997

Determination of okadaic acid by micellar electrokinetic chromatography with ultraviolet detection.

Micellar electrokinetic chromatography (MEKC) with ultraviolet (UV) detection was applied for the determination of non-derivatized phycotoxins associated with diarrhoetic shellfish poisoning. A detection limit for 40 pg of okadaic acid (OA) was achieved. The UV intensities of this toxin measured at 200 nm showed good linearity in the range 40-640 pg. OA was detected in mussels spiked with 10 ng/g whole tissue. The presence of OA and dinophysistoxin-2 was observed in the crude extract of the dinoflagellate Prorocentrum lima.

Animals↗
PubMed1997

A new method for determination of maitotoxin by capillary zone electrophoresis with ultraviolet detection.

Capillary zone electrophoresis with UV detection was applied to the rapid and efficient separation of an underivatized phycotoxin, maitotoxin, associated with ciguateric fish poisoning. Highly sensitive detection was obtained by UV absorption at 195 nm. A detection limit of 50 pg of maitotoxin was achieved at this wavelength. Analysis involved using a fused silica capillary coated with a hydrophobic phase, polyvinylalcohols. Confirmation of the electrophoretic peak of maitotoxin was further evaluated by cytotoxicity on a mammalian fibroblastic cell line, BHK 21 C13.

Animals↗