bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of conditions allowing the synthesis of acrylamide‐based monolithic microcolumns for capillary electrochromatography and of factors determining the retention of aromatic compounds on these stationary phases
Authors: Hoegger Daniela , Freitag Ruth 
Published: September 2003

AbstractThe influence of the cross‐linker (concentration), the porogen (lyotrophic salt) and the solvent type as well as the type and concentration of up to three “functional”, i.e., interactive monomers on the morphology and the chromatographic properties of acrylamide‐based hydrophilic monoliths are investigated. High total monomer concentrations favored polymers with a rigid rather than gel‐like structure. High cross‐linker concentrations also favor the formation of a nodular structure. The addition of a lyotrophic salt favors the formation of small nodules especially at higher monomer concentration; the pore size of the polymer can also be modulated through the salt concentration. Suitable monoliths were further investigated as potential stationary phases for capillary electrochromatography (CEC). Depending on the type and concentration of the monomers, plate numbers between 50 000 and 100 000 were routinely obtained. The standard deviation of the run‐to‐run reproducibility was below 2% and that of the batch‐to‐batch reproducibility below 5%. A set of nine hydrophobic and polar aromatic compounds (all noncharged) was used to investigate the retention mechanism. Possible candidates for chromatographic interaction and retention in these monoliths are the hydrophobic polymer backbone itself and the alkyl, carbonyl, hydroxy, amino, amide, and charged groups introduced by the various functional monomers. Judging from our results, the carbonyl and the hydroxy functions, as well as the hydrophobic polymer backbone can be supposed to be the main sites of interaction. The charged but also the alkyl functions seem to be less important in this regard. The polymerization conditions and especially the composition of the reaction mixture have a strong influence on the behavior of the final column.
Determination of heterocyclic aromatic amines by capillary electrophoresis coupled to mass spectrometry using in‐line preconcentration
Authors: Sentellas Sònia , Moyano Encarnación , Puignou Lluís , Galceran M. Teresa 
Published: September 2003

AbstractThis paper shows the potentiality of capillary electrophoresis (CE) coupled to mass spectrometry (MS) for the analysis of heterocyclic aromatic amines obtaining good results in terms of sensitivity and precision. These compounds have a special interest since they can be carcinogenic for humans. The optimization of a CE‐MS method was performed and the best conditions were obtained using a 16 mM formic acid/ammonium formate solution at pH 4.5 with 60% methanol as running electrolyte. For CE‐MS coupling, a sheath liquid methanol/20 mM formic acid (75/25) solution at a flow rate of 3μL/min and hydrodynamic injection of methanol mixtures for 10 s were used. Detection limits ranging from 18 ng/g to 360 ng/g and precisions up to 1.4% and 12% for migration time and concentration, respectively, were obtained. In order to improve sensitivity, field‐amplified sample injection was applied as an in‐line preconcentration method. Methanol/5 mM formic acid (50/50) as a sample solvent, 3 s hydrodynamic injection (0.5 psi) of a methanol plug, and 25 s of electrokinetic injection (10 kV) of the sample were found to be the optimum conditions. Detection limits up to 25 times lower and similar precisions than those reported for hydrodynamic injection were obtained.
Role of the charge in continuous beds in the chiral separation of hydroxy acids by ligand‐exchange capillary electrochromatography
Authors: Lecnik Oliver , Gübitz Gerald , Schmid Martin G. 
Published: September 2003

AbstractThis paper deals with the chiral separation of hydroxy acids using diallyl‐dimethylammonium chloride as a positive charge‐providing agent in the continuous bed. The chiral continuous bed was prepared by in situ copolymerization of monomers, including an L‐4‐hydroxyproline derivative as a chiral selector. This phase was applied to the chiral separation of hydroxy monocarboxylic acids and hydroxy dicarboxylic acids, respectively. The influence of both the selector concentration and the charge‐providing agent on retention and separation was investigated.
Capillary electrophoresis frontal analysis: Principles and applications for the study of drug‐plasma protein binding
Authors: Østergaard Jesper , Heegaard Niels H. H. 
Published: September 2003

AbstractCapillary electrophoresis is a well‐established technique for the study of noncovalent interactions. Various approaches exist and capillary electrophoresis‐frontal analysis provides an interesting alternative to the migration shift affinity capillary electrophoresis methods and conventional methods. The present work reviews the principles on which the frontal analysis method is founded. Advantages and limitations of capillary electrophoresis frontal analysis in comparison with both conventional and other capillary electrophoresis based methods for quantification of binding interactions are discussed. Investigations utilizing capillary electrophoresis‐frontal analysis have focused on the interaction of drugs with plasma proteins. These studies, primarily addressing the binding of drugs to human serum albumin, α1‐acid glycoprotein, and lipoproteins are reviewed together with some recent developments in capillary electrophoresis‐frontal analysis methodology.
Macroporous monolithic chiral stationary phases for capillary electrochromatography: New chiral monomer derived from cinchona alkaloid with enhanced enantioselectivity
Authors: Lämmerhofer Michael , Tobler Ernst , Zarbl Elfriede , Lindner Wolfgang , Svec Frantisek , Fréchet Jean M. J. 
Published: September 2003

AbstractA new chiral monomer derived from cinchona alkaloid, namely O‐9‐(tert‐butylcarbamoyl)‐11‐[2‐(methacryloyloxy)ethylthio]‐10,11‐dihydroquinine 1, was employed for the preparation of enantioselective monolithic capillary columns by an in situ copolymerization with 2‐hydroxyethyl methacrylate 2 (HEMA), ethylene dimethacrylate 3 (EDMA) in the presence of cyclohexanol and 1‐dodecanol as porogens (UV or thermal initiation of azobisisobutyronitrile (AIBN) as radical initiator). The porous properties and the electrochromatographic behavior of the new chiral monoliths were comparatively evaluated with previously described analogs obtained from O‐9‐[2‐(methacryloyloxy)ethylcarbamoyl]‐10,11‐dihydroquinidine 4 as chiral monomer. Despite close structural and physicochemical similarities of the both chiral monomers, the pore distribution profiles of the resulting monoliths were shifted typically towards larger pore diameters with the new monomer 1. Once more, it was confirmed that a low cross‐linking (10 wt% related to total monomers) and a pore diameter of about 1 μm in the dry state provides the best electrochromatographic efficiency as a result of lower resistance to mass transfer (smaller C‐term contribution to peak broadening) and more homogeneous flow profile (smaller A‐term). Most importantly, as expected the new poly(1‐co‐HEMA‐co‐EDMA) monoliths showed enhanced enantioselectivities and in addition faster separations as compared to poly(4‐co‐HEMA‐co‐EDMA) analogs, which represents a significant improvement. Further, the elution order was reversed owing to the pseudoenantiomeric behavior of quinine‐ and quinidine‐derived monomers. Fluorescence‐labeled 9‐fluorenylmethoxycarbonyl (FMOC), dansyl (DNS), 7‐dimethylaminosulfonyl‐1,3,2‐benzoxadiazol‐4‐yl (DBD), carbazole‐9‐carbonyl (CC) amino acids could be separated with resolution values between 2 and 4 (with efficiencies typically between 100 000 and 200 000 plates/m) and fluorescence detection (variable wavelength fluorescence detector in‐line with UV) yielding routinely a gain in detection sensitivities up to two orders of magnitude without specific optimization of the conditions with regards to fluorescence efficiency.
Multiple injection techniques for microfluidic sample handling
Authors: Fu Lung‐Ming , Yang Ruey‐Jen , Lee Gwo‐Bin , Pan Yu‐Jen 
Published: September 2003

AbstractThis paper presents an experimental and numerical investigation into electrokinetic focusing flow injection for bioanalytical applications on 1×N (i.e., 1 sample inlet port and N outlet ports) and M×N (i.e., M sample inlet ports and N outlet ports) microfluidic chips. A novel device is presented which integrates two important microfluidic phenomena, namely electrokinetic focusing and valveless flow switching within multiported microchannels. The study proposes a voltage control model which achieves electrokinetic focusing in a prefocusing sample injection system and which allows the volume of the sample to be controlled. Using the developed methods, the study shows how the sample may be prefocused electrokinetically into a narrow stream prior to being injected continuously into specified outlet ports. The microfluidic chips presented within this paper possess an exciting potential for use in a variety of techniques, including high‐throughput chemical analysis, cell fusion, fraction collection, fast sample mixing, and many other applications within the micrototalanalysis systems field.
A new micellar electrokinetic capillary chromatography method for separation of the components of the aminoglycoside antibiotics
Authors: Wienen Frank , Holzgrabe Ulrike 
Published: September 2003

AbstractAminoglycoside antibiotics are always a mixture of structurally related amino sugars, which do not have a chromophore or fluorophore. The aim of the study was to find one method for evaluation of the components and impurities of the antibiotics. Derivatization with o‐phthaldialdehyde and thioglycolic acid is found to be appropriate for all antibiotics. The components of gentamicin (GM), sisomicin, netilmicin, kanamycin, amikacin, and tobramycin were tried to separate by means of micellar electrokinetic chromatography. The background electrolyte was composed of sodium tetraborate (100 mM, pH 10.0), sodium deoxycholate (20 mM), and β‐cyclodextrin (15 mM). This method is valid for evaluation of GM, kanamycin, and tobramycin. It has to be improved for amikacin and netilmicin. In addition, 46 bulk samples of GM of different manufacturer or pharmaceutical companies were investigated. Many samples were found to contain many minor products and different amounts. Beside different patterns of the main compounds GM C1, GM C1a, GM C2a, and GM C2, many lots were found consisting of a substantial number of minor products. The appearance of a high number of minor products is always associated with the existence of sisomicin, which is not found in “pure” samples. However, almost all samples met the requirements of the European Pharmacopoeia (EP) and United States Pharmacopoeia (USP).
Microchip‐based capillary electrochromatography using packed beds
Authors: Jemere Abebaw B. , Oleschuk Richard D. , Harrison D. Jed 
Published: September 2003

AbstractIntegration of a packed column onto a microchip for performance of capillary electrochromatography (CEC) is described. The quartz device incorporated a cross‐injector, and a double weir trapping design for formation of 1, 2 and 5 mm long CEC columns. Three fluorescent dyes were baseline‐resolved with plate numbers of 330 (330 000 plates/m; height equivalent to a theoretical plate, H = 3.0 μm) for BODIPY 493/503, 360 (360 000 plates/m; H = 2.8 μm) for rhodamine 123 and 244 (244 000 plates/m; H = 4.1 μm) for acridine orange (AO) with 500 V applied on a 1 mm long column. The 2 mm column yielded ∼1.8 times more theoretical plates than did the 1 mm column, when operated at the same flow rate. Van Deemter plots were obtained for the three column lengths, showing increased plate height for the 5 mm length. A 2 mm column gave peak height and area relative standard deviation (RSD) values of 2.5 and 3.3%, respectively, as averages for the three dyes (n = 15). The RSD for the dye retention times was 1% (n = 6) over one day, and 3% (n = 30) over five days. Indirect fluorescence detection of thiourea and of amino acids was possible using a neutral indicator dye (BODIPY 493/503), with a detection limit of 10 μM for amino acids.
Bilayered phospholipid micelles and capillary electrophoresis: A new additive for electrokinetic chromatography
Authors: Holland Lisa A. , Leigh Alyison M. 
Published: September 2003

AbstractPhospholipid micelles and bilayered micelles (bicelles) were investigated as a new media for electrokinetic chromatography. The benefit to using these additives for micellar electrokinetic chromatography (MEKC) is the potential of a simple bilayer membrane model operated with fast analysis time, and low sample injection volumes. The system is used to separate peptides/protein and is tested with a series of beta‐blockers. The results suggest that bicelle electrokinetic chromatography provides selectivity and holds potential as an alternative approach to modeling membrane phenomenon.
Large‐volume sample stacking combined with separation by 2‐hydroxypropyl‐β‐cyclodextrin for analysis of isoxyzolylpenicillins by capillary electrophoresis
Authors: Zhu Zhiwei , Zhang Lifeng , Marimuthu Arun , Yang Zhaoguang 
Published: September 2003

AbstractA simple, quick and sensitive capillary electrophoretic technique has been developed for the pharmaceutical analysis of isoxazolylpenicillins (oxacillin, cloxacillin and dicloxacillin) at trace levels for the first time. This method comprises large‐volume sample stacking using the electroosmotic flow (EOF) pump (LVSEP), separation using 2‐hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) as selective complex‐forming background electrolyte additive, and direct UV detection. A complete resolution was achieved in the optimal background electrolyte containing 5.2 mM HP‐β‐CD. LVSEP was successfully applied in their determinations to improve the sensitivity, where the EOF in the buffer zone was suppressed by using an acidic buffer with pH 3.6. The detection limits of the current technique were found to be 2.0 μg/L for each of the isoxazolylpenicillins based on the signal‐to‐noise ratio of 3. The curves of peak response versus concentration were linear from 5.0 to 400.0 μg/L with regression coefficients of 0.9982, 0.9986 and 0.9976, respectively. The interaction of isoxazolylpenicillins with HP‐β‐CD was discussed. The association constants for complexes of HP‐β‐CD with isoxazolylpenicillins were determined by electrophoretic method. The obtained association constants were 27.3, 34.9, and 48.5 M−1, respectively, being proportional to their hydrophobic properties and steric hindrances. A simple and easy‐manipulative sample preparation method was developed and validated by analyzing commercially available milk samples. It was found that with current sample preparation process and instrumentation system, 0.1 mL of milk sample is enough for the analysis of isoxazolylpenicillins to meet European Union (EU) guideline of 30 μg/kg.
Effect of multivalent ions on electroosmotic flow in micro‐ and nanochannels
Authors: Zheng Zhi , Hansford Derek J. , Conlisk Albert T. 
Published: September 2003

AbstractIn this work, the effect of multivalent ions on electroosmotic flow is investigated for multiple electrolyte components. The cases studied include incorporating Ca2+ and HPO42‐ and other monovalent ions, such as K+ and H2PO4‐, into an aqueous NaCl solution. The governing equations are derived and solved numerically. The boundary conditions for the governing equations are obtained from the electrochemical equilibrium requirements. In comparison with monovalent ions, the results show that in micro‐ and nanochannels having fixed surface charges, multivalent counterions, even in very small amounts, reduce electroosmotic flow significantly, while the multivalent co‐ions have little effect on the electroosmotic flow. Due to the enhanced ion‐wall interactions multivalent counterions compose the majority of ions in the electric double layer (EDL), causing a decrease of net charge at the surface.
Complexation trends and binding constants between dextrin oligomers and small molecules as measured through affinity capillary electrophoresis
Authors: Hoffmann Julia , Mechref Yehia , Cassely Aaron , Novotny Milos V. 
Published: September 2003

AbstractQuantitative aspects of a previously reported pre‐equilibration affinity/capillary electrophoretic methodology (Hong, M., et al., Anal. Chem. 1998, 70, 3590–3597) were studied using fluorescently labeled oligosaccharides and analgesic drugs. Frontal analysis capillary electrophoresis (FA‐CE) was investigated for these interaction systems. In order to fulfill certain FA requirements, the analysis conditions of the sugar‐drug combinations had to be adjusted individually. Only after the establishment of these conditions, acceptable binding data (association constants) could be obtained. The constants are in the range of weak hydrogen bonding and are comparable to the constants that were independently obtained through 1H nuclear magnetic resonance (NMR) spectroscopy.
Validation of capillary electrophoresis – mass spectrometry methods for the analysis of a pharmaceutical formulation
Authors: Geiser Laurent , Rudaz Serge , Veuthey Jean‐Luc 
Published: September 2003

AbstractThe coupling of capillary electrophoresis (CE) to mass spectrometry (MS) with an electrospray ionization (ESI) technique is generally performed for qualitative applications, and only few quantitative results have been reported. This paper investigates the validation of a CE‐ESI‐MS method for the analysis of a pharmaceutical formulation containing lidocaine. Some important ESI criteria are discussed including sheath‐liquid composition, nebulizing gas pressure and position of the CE capillary outlet. After optimization of these parameters, an intermediate precision of about 5% was achieved. The latter, as well as efficiency and resolution, were compared to those achieved with UV detection. Besides, a multiple injection procedure was developed to reduce analysis time per sample and was successfully applied to both UV and MS detectors. The validation results achieved by multiple injections were identical to those obtained with classical injection, but afforded a gain of time by a factor of 2.5.
Capillary electrophoresis – electrospray ionization – mass spectrometry for the characterization of natural organic matter: An evaluation with free flow electrophoresis‐off‐line flow injection electrospray ionization‐mass spectrometry
Authors: Schmitt‐Kopplin Philippe , Kettrup Antonius 
Published: September 2003

AbstractThe separation of Suwannee River natural organic matter (NOM) with capillary zone electrophoresis hyphenated to electrospray ionization‐mass spectrometry (CZE‐ESI‐MS) is presented. The obtained electropherograms and signal distributions are comparable to the mobility distributions obtained with more classical UV detection. A direct comparison of the results was possible with free‐flow electrophoresis (FFE), which allows an upscaling of the CZE method and the analysis of the collected fractions in an off‐line modus with flow‐injection electrospray ionization‐mass spectrometry (FI‐ESI‐MS). The changes of the m/z distributions with mobility are very similar with both methods and show a decrease of the m/z with increasing electrophoretic mobility in the humic hump at alkaline pH; superimposed on this hump a low‐molecular‐weight fraction migrates at lower mobility. The analysis of benzene carboxylic acids, glycerrhycic acid as well as oligomers of polystyrene sulfonic acid and polyacrylic acid additionally illustrates possible fragmentation, formation of adducts and multiplicity of the charges of the molecules prior to MS detection. These hardly controllable difficulties add a challenge to the interpretation of the obtained m/z distributions of NOM in terms of charge and mass distributions of molecules present in the NOM mixture.
Analysis of N‐acyl‐L‐homoserine lactones produced by Burkholderia cepacia with partial filling micellar electrokinetic chromatography – electrospray ionization‐ion trap mass spectrometry
Authors: Frommberger Moritz , Schmitt‐Kopplin Philippe , Menzinger Franz , Albrecht Valerie , Schmid Michael , Eberl Leo , Hartmann Anton , Kettrup Antonius 
Published: September 2003

AbstractA method for the analysis of N‐acyl‐L‐homoserine lactones (AHLs) with micellar electrokinetic chromatography coupled to electrospray ionization‐ion trap mass spectrometry, combining the flexibility of capillary electrophoresis with the unmatched structural information provided by mass spectrometry is presented. Different surfactants were evaluated, with sodium dodecyl sulfate (SDS) yielding the best results considering sensitivity and flexibility. We examined the interaction of AHLs with the SDS micelles at different analysis conditions and applied the optimized method to the analysis of a real bacterial sample. Two AHLs from Burkholderia cepacia colonizing the rhizosphere of traditional Indian rice cultivars could be unambiguously determined in an ethyl acetate extract with high resolution flexibility.
Recent developments in capillary electrokinetic chromatography with replaceable charged pseudostationary phases or additives
Authors: Perič Iván , Kenndler Ernst 
Published: September 2003

AbstractAlthough electrochromatography in packed beds or monolithic columns has gained enormous interest, techniques based on charged pseudostationary phases like micelles are of high practical importance in electrically driven separation science. However, nonmicellar alternatives, e.g., using charged soluble polymers or smaller additives are still attractive, as they allow high concentrations of organic solvents, and their application is not limited by the critical micellar concentration. This review discusses the developments in the field of electrokinetic chromatography with these additives in the last three years, covering ionic polymeric pseudostationary phases, dendrimers and so‐called micelle polymers, but also small molecules which implement separation selectivity due to their specific interaction with the analytes.
Mother–child and metapelet–child touch behavior with three‐year‐old kibbutz children in two contexts
Authors: Landau Rivka , Shusel Ronit , Eshel Yohanan , Ben‐Aaron Miriam 
Published: September 2003

AbstractThe frequency and function of self‐touch and of touching another was studied among 32 three‐year‐old kibbutz children, their mothers, and their metaplot [caretakers; singular: metapelet] in two contexts: coconstruction of a narrative with Duplo toys, and coconstruction of a narrative with an emotion‐evoking picture book without text. Self‐touch, mainly fidgeting, was more frequent for children during the task with the picture book and more frequent for adults during the task with the Duplo toys. Mothers and children touched each other more often than metaplot and children. Adults' touches of the children were perceived as either expressions of affection or as acts of grooming and were task‐related. The children's touching of the adults was mainly task‐related. It appears that self‐touch is for children and adults alike a mode of self‐regulation of mild stress and that touching the other has a wide range of functions, especially in intimate relationships. ©2003 Michigan Association for Infant Mental Health.