bluuebunny/crossref_metadata_2025_split huggingface dataset:
Separation of twenty underivatized essential amino acids by capillary zone electrophoresis with contactless conductivity detection
Authors: Coufal Pavel , Zuska Jiří , van de Goor Tom , Smith Vonda , Gaš Bohuslav 
Published: February 2003

AbstractTwenty underivatized essential amino acids were separated using capillary zone electrophoresis and consequently detected with contactless conductivity detection (CCD). A simple acidic background electrolyte (BGE) containing 2.3 M acetic acid and 0.1% w/w hydroxyethylcellulose (HEC) allowed the electrophoretic separation and sensitive detection of all 20 essential amino acids in their underivatized cationic form. The addition of HEC to the BGE suppressed both, electroosmotic flow and analyte adsorption on the capillary surface resulting in an excellent migration time reproducibility and a very good analyte peak symmetry. Additionally, the HEC addition significantly reduced the noise and long‐term fluctuations of the CCD baseline. The optimized electrophoretic separation method together with the CCD was proved to be a powerful technique for determination of amino acid profiles in various natural samples, like beer, yeast, urine, saliva, and herb extracts.
Differences in capillary electrophoresis profiles of urinary and recombinant erythropoietin
Authors: de Frutos Mercedes , Cifuentes Alejandro , Diez‐Masa Jose C. 
Published: February 2003

AbstractDifferent profiles were obtained by capillary zone electrophoresis (CZE) of human erythropoietin (EPO) of recombinant and urinary origin. To unambiguously detect doping by EPO, direct methods able to determine the presence of the drug itself in a physiological fluid are required. Since the host cell line used for EPO production influences its glycosylation, the carbohydrate distribution of natural human EPO may be different from that of recombinant EPO. The different content in sialic acid groups between recombinant and endogenous EPO provide a basis for their distinction by CZE.
Separation of homologues and isomers of linear alkylbenzenesulfonates by capillary electrophoresis with sodium dodecyl sulfate, carboxylic acids and bile salts
Authors: Herrero‐Martínez José Manuel , Simó‐Alfonso Ernesto F. , Ramis‐Ramos Guillermo 
Published: February 2003

AbstractThe ability of several anionic compounds, including carboxylic and dicarboxylic acids, sodium dodecyl sulfate (SDS), and sodium deoxycholate (SDC) and other bile salts, to separate the C10–C13 homologues and the corresponding 20 positional isomers of linear alkylbenzenesulfonates (LAS) by capillary electrophoresis was studied. Up to 19 peaks and a shoulder were observed with a background electrolyte (BGE) containing 10 mM phosphate (pH 6.8), 30% acetonitrile and 40 mM SDS, and 18 peaks were obtained with a BGE containing 10 mM borate (pH 9), 40% ethanol and 40 mM palmitic acid (PA). Resolution increased with the alkyl chain length of the carboxylic acid. Dicarboxylic acids with a short alkyl chain, as azelaic acid, were useful to separate the homologues without distinguishing between the isomers. Up to 16 peaks and a shoulder were distinguished with SDC. Resolution decreased with the other bile salts. The 6‐C11/5‐C11 isomer pair was better resolved with SDC than with SDS, and the 2‐C12 isomer was isolated using both PA and SDC, but not with SDS. Only the 7‐C13/6‐C13 pair could not be resolved with any of the discriminating agents used.
Micellar electrokinetic chromatography with on‐line Fourier transform infrared detection
Authors: Kölhed Malin , Hinsmann Peter , Lendl Bernhard , Karlberg Bo 
Published: February 2003

AbstractMicellar electrokinetic chromatography (MEKC) was successfully coupled to Fourier transform infrared (FTIR) detection, using a micromachined IR‐transparent flow cell with an optical path length of 15 μm for the on‐line detection of five neutral analytes. Tight connections between the flow cell and the capillaries were achieved by creating a small O‐ring of UV‐curing epoxy adhesive on the sharply cut capillary ends. The background electrolyte consisted of 15 mM phosphate buffer at pH 7 and 40 mM sodium dodecyl sulfate (SDS). Five analytes (paracetamol, caffeine, p‐nitro benzyl alcohol, m‐nitrophenol and p‐nitrophenol) were successfully separated, yielding detailed IR stack plots that could be used for quantification and identification. Linear calibration graphs were obtained for each individual analyte present in mixtures at concentrations up to 10 mM. The limit of detection (3 S/N) ranged between 1.1 and 1.5 mM (1.2–1.8 ng). Analytes were identified by comparing spectra obtained during the MEKC separation with those resulting from completely filling the capillary with each individual analyte dissolved in the micelle‐containing electrolyte. Information on the specific functional groups of all analytes could be elucidated from the spectra. Since FTIR is a nondestructive detection technique, a conventional on‐line UV detector was introduced directly after the developed IR flow cell to test the system's performance and to demonstrate that tandem FTIR and UV detection is feasible.
Chromatographic behavior of packing materials for capillary electrochromatography with a coating of different immobilized polysiloxanes
Authors: Zhang Guodong , li Yongshan , Fang Yi'ou , Han Nanyin , Xu Bingjiu 
Published: February 2003

AbstractOctadecyl silyl silica (ODS) phase coated with immobilized polysiloxanes (OV1701, SE‐54, SE‐30) were synthesized, their characteristics as capillary electrochromatography (CEC) column packing materials were studied. It was found that, although the polysiloxane coatings were different in polarity, the resulting packing materials showed the highest efficiencies when the respective coating ratios (polysiloxane:ODS, w/w) were all 20–30%. As expected, packing materials coated with different polysiloxanes resulted in different selectivity on solute pairs. Separations on these stationary phases were studied with different factors such as pH values and acetonitrile contents of the mobile phases. It was found that all these kind of stationary phases could resist basic mobile phase with a pH value as high as 11.6. Tests were made to analyze polar, basic drugs with CEC using the stationary phases.
Determination of low‐aliphatic aldehydes indoors by micellar electrokinetic chromatography using sample dissolution manipulation for signal enhancement
Authors: Pereira Elisabete A. , Cardoso Arnaldo A. , Tavares Marina F. M. 
Published: February 2003

AbstractThis work describes a novel approach for the analysis of selected aldehydes (formaldehyde, acetaldehyde, propionaldehyde, and acrolein) and acetone in environmental samples using micellar electrokinetic chromatography (MEKC). The method is based on the reaction of carbonyl compounds with 3‐methyl‐2‐benzothiazoline hydrazone (MBTH) that gives an azine intermediate with maximum absorbance at 216 nm. A systematic evaluation of sample dissolution medium was conducted as a means to enhancing sensitivity. In the best condition, samples were dissolved in 0.030 mol·L−1 tetraborate solution. This condition presented enhancement factors in the range of 35–54 for the aldehydes under investigation, computed as the improvement of the concentration limits of detection (LODs) with reference to the sample dissolved in pure water. The running buffer was 0.020 mol·L−1 tetraborate, pH 9.3, containing 0.050 mol·L−1 sodium dodecyly sulfate (SDS). The overall methodology presented several advantages over established methods for aldehydes. Worthy mentioning that MBTH is available in high purity degree, dispensing laborious reagent purification procedures. A few method validation parameters were determined revealing good migration time repeatability (< 2.5% coefficient of variation, CV) and area repeatability (< 4% CV), excellent linearity (20–120 μg/L, r > 0.995) and adequate sensitivity for environmental applications. The LODs with respect to each single aldehyde were in the range of 0.54–4.0 μg·L−1 and 11 μg·L−1 for acetone. The methodology was applied to the determination of aldehydes indoors. Samples were collected in an impinger flask containing 0.05% MBTH solution, at a flow rate of 0.80 L·min−1, during 2.5 h, at different times during the day. The most abundant carbonyls in the samples were acetone, followed by formaldehyde and acetaldehyde, with estimate peak concentrations of 452, 5.2 and 2.2 ppbv, respectively.
Mixed micellar electrokinetic capillary chromatography separation of depolymerized grape procyanidins
Authors: Herrero‐Martínez José Manuel , Ràfols Clara , Rosés Martí , Torres Josep Lluís , Bosch Elisabeth 
Published: February 2003

AbstractOligomeric procyanidins are potent antioxidant polyphenols of potential interest as disease‐preventing agents. Their efficiency depends on the size and composition of their oligomeric structures. The mean degree of polymerization of these compounds is usually estimated by thiolysis with thiol‐α‐toluene followed by analysis using high‐performance liquid chromatography (HPLC). We show the development of a mixed micellar electrokinetic chromatography (MEKC) method for the separation of the major components obtained after thiolysis with cysteamine (catechins and their cysteamine conjugates). MEKC studies using sodium dodecyl sulfate (SDS as pseudostationary phase led to long migration times, e.g., with 100 mM SDS, at pH 7, the solutes were separated in about 40 min), while the use of sodium cholate (SC) produced an elution window relatively short. Using a mixed micellar SC‐SDS system (50 mM phosphate at pH 7 containing 40 mM SC and 10 mM SDS), it is possible to separate these compounds in less than 15 min. The proposed method is useful to separate the major components of the thiolysate in effluents from food processing (e.g., skins and seeds from grape and apple) considered as potential procyanidin sources.
Ultrafast analysis of oligosaccharides on microchip with light‐emitting diode confocal fluorescence detection
Authors: Dang Fuquan , Zhang Lihua , Hagiwara Hisashi , Mishina Yoshinori , Baba Yoshinobu 
Published: February 2003

AbstractWe have developed a new method for the high‐speed separation and high‐sensitivity detection of complex oligosaccharides based on microchip electrophoresis (ν‐CE) with light‐emitting diode (LED) confocal fluorescence detection. Oligosaccharides labeled with 8‐aminopyrene‐1,3,6‐trisulfonate (APTS) were found to strongly adsorb to the surface of polymethylmethacrylate (PMMA) microchips. Accordingly, three classes of major dynamic coating additives were systematically investigated, and cellulose derivatives were found to specifically suppress such adsorption and allow high‐performance separation on PMMA chips. Additive concentration, buffer pH and applied field strength were found to be key factors in the high‐performance separation& of APTS‐labeled oligosaccharides on PMMA chips. Under optimal conditions, 15 oligosaccharides in dextrin hydrolysate can be separated within 45 s with an electrophoretic separation efficiency of over 400 000 theoretical plates per meter. The relative standard deviation (RSD) values of migration times of fourteen oligosaccharides were less than 0.50% between six different channels, and the detection limit for APTS‐labeled glucose was about 1.98×10−8 mol/L or 8.61 amol with a signal‐to‐noise ratio (S/N) of 3. The high speed, high efficiency and high sensitivity of this μ‐CE‐based method indicate that it can be widely applied to analysis of complex oligosaccharides.
Microdevices for manipulation and accumulation of micro‐ and nanoparticles by dielectrophoresis
Authors: Dürr Manfried , Kentsch Jörg , Müller Torsten , Schnelle Thomas , Stelzle Martin 
Published: February 2003

AbstractMicrofluidic devices with three‐dimensional (3‐D) arrays of microelectrodes embedded in microchannels have been developed to study dielectrophoretic forces acting on synthetic micro‐ and nanoparticles. In particular, so‐called deflector structures were used to separate particles according to their size and to enable accumulation of a fraction of interest into a small sample volume for further analysis. Particle velocity within the microchannels was measured by video microscopy and the hydrodynamic friction forces exerted on deflected particles were determined according to Stokes law. These results lead to an absolute measure of the dielectrophoretic forces and allowed for a quantitative test of the underlying theory. In summary, the influence of channel height, particle size, buffer composition, electric field, strength and frequency on the dielectrophoretic force and the effectiveness of dielectrophoretic deflection structures were determined. For this purpose, microfluidic devices have been developed comprising pairs of electrodes extending into fluid channels on both top and bottom side of the microfluidic channels. Electrodes were aligned under angles varying from 0 to 75° with respect to the direction of flow. Devices with channel height varying between 5 and 50 μm were manufactured. Fabrication involved a dedicated bonding technology using a mask aligner and UV‐curing adhesive. Particles with radius ranging from 250 nm to 12 μm were injected into the channels using aqueous buffer solutions.
In‐column field‐amplified sample stacking of biogenic amines on microfabricated electrophoresis devices
Authors: Beard Nigel P. , Zhang Chao‐Xuan , deMello Andrew J. 
Published: February 2003

AbstractA novel method for performing in‐column field‐amplified sample stacking (FASS) in chip‐based electrophoretic systems is presented. The methodology involves the use of a narrow sample channel (NSC) injector. NSC injectors allow sample plugs to be introduced directly into the separation channel, and subsequent stacking and separation can proceed without any need for leakage control. More importantly, stacking and separation occur in a single step negating the requirement for complex channel geometries and voltage switching to control sample plugs during the stacking procedure. The chip is composed of six paralleled systems. Using the NSC injector design, the number of reservoirs in the multiplexed chip is reduced to N + 2, where N is the number of paralleled systems. This design feature radically reduces the complexity in chip structures and associated chip operation. The approach is applied to the analysis of fluorescently labelled biogenic amines affording detection at concentrations down to 20 pM.
Analysis of the quorum‐sensing regulon of the opportunistic pathogen Burkholderia cepacia H111 by proteomics
Authors: Riedel Kathrin , Arevalo‐Ferro Catalina , Reil Gerold , Görg Angelika , Lottspeich Friedrich , Eberl Leo 
Published: February 2003

AbstractBurkholderia cepacia H111, an important pathogen for persons suffering from cystic fibrosis, employs a quorum‐sensing (QS) system, cep, to control expression of virulence factors as well as the formation of biofilms. The QS system is thought to ensure that pathogenic traits are only expressed when the bacterial population density is high enough to overwhelm the host before it is able to mount an efficient response. In this study, we compared the protein pattern of the intracellular, extracellular, and surface protein fractions of an AHL‐deficient cepI mutant with the one of the parent strain H111 by means of two‐dimensional gel electrophoresis (2‐DE). Our analysis showed that 55 proteins out of 985 detected spots were differentially expressed; these are expected to represent QS‐controlled gene products. Addition of the respective signal molecules to the growth medium of the cep mutant fully restored the wild‐type protein expression profile. In total about 5% of the B. cepacia proteome was downregulated and 1% upregulated in the cepI mutant, indicating that quorum sensing represents a global regulatory system. Nineteen proteins were identified with high confidence by N‐terminal sequence analysis.
Sodium dodecyl sulfate versus acid‐labile surfactant gel electrophoresis: Comparative proteomic studies on rat retina and mouse brain
Authors: König Simone , Schmidt Oliver , Rose Karin , Thanos Solon , Besselmann Michael , Zeller Martin 
Published: February 2003

AbstractA long‐chain derivative of 1,3‐dioxolane sodium propyloxy sulfate, with similar denaturing and electrophoretic properties as SDS, and facilitated protein identification following polyacrylamide gel electrophoresis (PAGE) for Coomassie‐stained protein bands, has been tested. Comparative acid‐labile surfactant/sodium dodecyl sulfate two‐dimensional (ALS/SDS 2‐D)‐PAGE experiments of lower abundant proteins from the proteomes of regenerating rat retina and mouse brain show that peptide recovery for mass spectrometry (MS) mapping is significantly enhanced using ALS leading to more successful database searches. ALS may influence some procedures in proteomic analysis such as the determination of protein content and methods need to be adjusted to that effect. The promising results of the use of ALS in bioanalytics call for detailed physicochemical investigations of surfactant properties.
Multiple polypeptide forms observed in two‐dimensional gels of Methylococcus capsulatus (Bath) polypeptides are generated during the separation procedure
Authors: Berven Frode S. , Karlsen Odd A. , Murrell J. Colin , Jensen Harald B. 
Published: February 2003

AbstractWe have examined two‐dimensional electrophoresis (2‐DE) gel maps of polypeptides from the Gram‐negative bacterium Methylococcus capsulatus (Bath) and found the same widespread trains of spots as often reported in 2‐DE gels of polypeptides of other Gram‐negative bacteria. Some of the trains of polypeptides, both from the outer membrane and soluble protein fraction, were shown to be generated during the separation procedure of 2‐DE, and not by covalent post‐translational modifications. The trains were found to be regenerated when rerunning individual polypeptide spots. The polypeptides analysed giving this type of trains were all found to be classified as stable polypeptides according to the instability index of Guruprasad et al. (Protein Eng. 1990, 4, 155–161). The phenomenon most likely reflects conformational equilibria of polypeptides arising from the experimental conditions used, and is a clear drawback of the standard 2‐DE procedure, making the gel picture unnecessarily complex to analyse.
The use of dynamic grid adaptation algorithms for the modelling of flow around a circular cylinder in sub‐critical flow regime
Authors: de With G. , Holdø A. E. , Huld T. A. 
Published: February 2003

AbstractIn the present study a dynamic grid adaptation (DGA) algorithm is utilized for predicting flow around a circular cylinder in sub‐critical flow regime at a Reynolds number of 1.4×105. The reason for adopting a DGA algorithm is the unsteadiness of the flow field which makes a conventional mesh inefficient. The concept being adopted is to concentrate mesh refinement in regions with high gradients and high turbulent viscosity, while in the region further downstream where the flow is fully developed a coarser mesh will develop and turbulence is modelled with the large eddy simulation (LES) turbulence model.The aim of the study is to present an appropriate variable for mesh refinement, which accomplishes a high rate of mesh refinement in the region with high gradients. The new variable is a product of the local mesh cell size and the rate of strain and includes two additional variables to allow control over the refinement behaviour. The results are compared with experimental data at the corresponding Reynolds number and also with numerical results obtained with conventional mesh. It is demonstrated that DGA algorithms can give results of a very high quality for a mesh that is significantly smaller than for a conventional mesh. Copyright © 2003 John Wiley & Sons, Ltd.
Parallel finite element simulation of mooring forces on floating objects
Authors: Aliabadi S. , Abedi J. , Zellars B. 
Published: February 2003

AbstractThe coupling between the equations governing the free‐surface flows, the six degrees of freedom non‐linear rigid body dynamics, the linear elasticity equations for mesh‐moving and the cables has resulted in a fluid‐structure interaction technology capable of simulating mooring forces on floating objects. The finite element solution strategy is based on a combination approach derived from fixed‐mesh and moving‐mesh techniques. Here, the free‐surface flow simulations are based on the Navier–Stokes equations written for two incompressible fluids where the impact of one fluid on the other one is extremely small. An interface function with two distinct values is used to locate the position of the free‐surface. The stabilized finite element formulations are written and integrated in an arbitrary Lagrangian–Eulerian domain. This allows us to handle the motion of the time dependent geometries. Forces and momentums exerted on the floating object by both water and hawsers are calculated and used to update the position of the floating object in time. In the mesh moving scheme, we assume that the computational domain is made of elastic materials. The linear elasticity equations are solved to obtain the displacements for each computational node. The non‐linear rigid body dynamics equations are coupled with the governing equations of fluid flow and are solved simultaneously to update the position of the floating object. The numerical examples includes a 3D simulation of water waves impacting on a moored floating box and a model boat and simulation of floating object under water constrained with a cable. Copyright © 2003 John Wiley & Sons, Ltd.
Rotary oscillations of axi‐symmetric bodies in an axi‐symmetric viscous flow with slip: Numerical solutions for sphere and spheroids
Authors: Tekasakul P. , Loyalka S. K. 
Published: February 2003

AbstractRotary oscillations of several axi‐symmetric bodies in axi‐symmetric viscous flows with slip are investigated. A numerical method based on the Green's function technique is used wherein the relevant Helmholtz equation, as obtained from the unsteady Stokes equation, is converted into a surface integral equation. The technique is benchmarked against a known analytical solution, and accurate numerical results for local stress and torque on spheres and spheroids as function of the frequency parameter and the slip coefficients are obtained. It is found that in all cases, slip reduces stress and torque, and increasingly so with the increasing frequency parameter. The method discussed here can be potentially extended to the realistic case of an oscillating disk viscometer. Copyright © 2003 John Wiley & Sons, Ltd.
Central schemes for open‐channel flow
Authors: Gottardi Guido , Venutelli Maurizio 
Published: February 2003

AbstractThe resolution of the Saint‐Venant equations for modelling shock phenomena in open‐channel flow by using the second‐order central schemes of Nessyahu and Tadmor (NT) and Kurganov and Tadmor (KT) is presented. The performances of the two schemes that we have extended to the non‐homogeneous case and that of the classical first‐order Lax–Friedrichs (LF) scheme in predicting dam‐break and hydraulic jumps in rectangular open channels are investigated on the basis of different numerical and physical conditions. The efficiency and robustness of the schemes are tested by comparing model results with analytical or experimental solutions. Copyright © 2003 John Wiley & Sons, Ltd.