bluuebunny/crossref_metadata_2025_split huggingface dataset:
Systematic optimization of capillary electrophoretic separations using the overlapping resolution mapping scheme
Authors: Ng Choon Lan , Ong Chye Peng , Lee Hian Kee , Li Sam Fong Yau 
Published: May 2005

AbstractIn this study, the use of a systematic optimization scheme for capillary electrophoretic separations is described. This scheme utilizes the overlapping resolution mapping procedure to predict the optimum separation conditions for the separation of two groups of compounds, a group of seven flavonoids and a group of eight sulfonamides. The chosen parameters that affect the separation depend on the compounds in question. In the case of flavonoids, pH and SDS concentrations were chosen as the parameters for optimization, whereas in the case of sulfonamides, pH and β‐cyclodextrin concentrations were used. As few as nine experiments are required to achieve optimum conditions for the separation of all peaks. To confirm the validity of the optimization procedure, additional experiments chosen from the predicted optimum conditions were performed. The results show that satisfactory separation could be achieved by using the optimum conditions predicted by the scheme. All flavonoid and sulfonamide peaks were satisfactorily separated in about 30 and 8 min, respectively.
Use of a sheath flow cuvette for chemiluminescence detection of isoluminol thiocarbamyl‐amino acids separated by capillary electrophoresis
Authors: Zhao Jian‐Ying , Labbe Jill , Dovichi Norman J. 
Published: May 2005

AbstractA post‐column reactor was designed for chemiluminescence detection in the capillary electrophoresis separation of isoluminol thiocarbamyl derivatives of amino acids. This system was characterized with respect to hydrogen peroxide concentration and flow rate, surfactant concentration, microperoxidase concentration, and mixing distance. A linear calibration curve (R >0.999) was constructed for isoluminol ranging from at least 30 femtomoles to the detection limit of 40 attomoles injected; the dynamic range of the instrument is at least three orders of magnitude. Detection limit for the isoluminol thiocarbamyl derivative of valine was 500 attomoles. The theoretical plate counts for the raw data are typically 1 × 105 for labeled amino acids, and a factor of two better for isoluminol.
Novel detection schemes for the trace analysis of amino acids and peptides using capillary electrophoresis
Authors: Sweedler Jonathan V. , Fuller Robert , Timperman Scott Tracht Aaron , Toma Verna , Khatib Karim 
Published: May 2005

AbstractThe ability of the cellular biochemist to understand events occurring in small subsections of an individual cell depends on available analytical techniques. Two unique capillary electrophoresis (CE) detection schemes for trace level peptide analysis are characterized: an on‐line, multichannel, laser‐induced fluorescence system and a post‐column radionuclide system. The fluorescence system has picomolar concentration detection limits (and zeptomole mass limits of detection) for tagged amino acids and peptides. Preliminary results are presented for a method to enhance the ability to fluorescently tag low concentrations of amino acids and peptides from neuronal subsections. The procedure takes advantage of the high local concentration of peptides within a synaptic vesicle to enhance the derivatization reaction. The other detection method described involves a post‐column35S detector to examine methionine or cysteine containing peptides. This system deposits the effluent from the separation capillary onto a membrane treated with a solid scintillator. After drying the membrane, the photon emission is imaged with a solid‐state integrating detector. The sensitivity for 35S labeled components is in the attomole range.
High‐speed GC/MS using narrow‐bore columns and ion trap detection
Authors: van Ysacker Peter G. , Janssen Hans‐Gerd M. , Snijders Henri M. J. , Leclercq Piet A. , Cramers Carel A. , van Cruchten Huub J. M. 
Published: May 2005

AbstractFast gas chromatographic separations can be achieved by vacuum‐outlet operation and by applying narrow‐bore columns. In this work, the combination of 50 μm i.d. columns with ion trap mass spectrometric detection is evaluated. Detection limits in the electron ionization mode, and in the chemical ionization mode using CH4 as the reaction gas, are 1 pg and 5 pg, respectively. Owing to the high sensitivity of the ion trap mass spectrometer, a significant improvement in the working range in comparison with other detection systems is obtained. The small column flows cause no loss of mass spectral resolution and sensitivity. The performance of the system is demonstrated by the analysis of some real‐world samples.
Electrophoretic focusing in a natural steady state moving pH gradient
Authors: Šlais Karel 
Published: May 2005

AbstractThe physical and mathematical basic of a natural steady state, moving pH gradient is outlined. With certain approximations, a differential equation of the concentration of the component contributing to the natural steady state, moving pH gradient is formulated. Solutions of the differential equation and the relationships to the resolution calculations of both carriers and trace components present in the large excesses of carriers are presented. The steady state distribution profiles of both amphoteric and nonamphoteric components predict Gaussian distributions only if and when the conductivity and the pH gradient remain constant within the moving focused zone. The practical significance of the model is shown by its application to isoelectric focusing (IEF) with electrophoretic mobilization, to isotachophoresis (ITP) with polyampholytic spacers, and to related methods. It is shown that the presented approximate model represents the transition between classical models of IEF and ITP.
Evaluation of solvent venting with a gas purge for the introduction of microliter sample volumes in supercritical fluid chromatography
Authors: Berg Bjørn E. , Hansen Ellen M. , Flaaten Anne M. , Greibrokk Tyge 
Published: May 2005

AbstractPeak broadening and sample recovery are important considerations when working with large sample volume injections in capillary SFC. To measure possible contribution to peak broadening in the venting valve, a tee coupling was inserted between the retention gap and the column. A standard sample containing glyceryl esters was injected. Based on time variance measurements, the venting valve did not lead to measurable band broadening. Recovery was found to be dependent on the length of the retention gap, the CO2/He ratio in the purge gas, and the temperature of the retention gap. Cryofocusing was needed to increase the recoveries of volatile n‐alkanes. To increase the recoveries of glyceryl esters, an enhanced CO2/He ratio was needed.
Importance of molecular shape in supercritical fluid chromatography using a porous glassy carbon adsorbent stationary phase
Authors: Larkins William C. , Olesik Susan V. 
Published: May 2005

AbstractThe effect of a solute's shape on retention using porous glassy carbon (PGC) as a stationary phase in supercritical fluid chromatography (SFC) is described. A series of stilbene and stilbene‐like molecules that have similar solvatochromic parameters but markedly different three dimensional configurations was used to explore the possible effects of molecule shape on PGC adsorption. The extent of π‐π interactions between the solutes (stilbene and stilbene‐like molecules) and the carbon surface was predominately controlled by the three‐dimensional shape of the solutes. In every case the planarity of the solute correlated with the retention of the solute.
Diluted modified cyclodextrins as chiral capillary gas chromatographic stationary phases: Influence of the polysiloxane solvents on enantioselectivity and column efficiency
Authors: Dietrich Armin , Maas Birgit , Mosandl Armin 
Published: May 2005

AbstractThe influence of different polysiloxane solvents on the efficiency and stereoselectivity of columns coated with mixtures of heptakis(2,3‐di‐O‐methyl‐6‐O‐tert‐butyldimethylsilyl)‐β‐cyclodextrin (DIME‐6‐TBDMS‐β‐CD) and the polysiloxanes was investigated. In the case of DIME‐6‐TBDMS‐β‐CD, the enantioselectivity of the chiral selector is strongly influenced by the polysiloxane used as diluting phase. Enantioselectivities achieved using apolar polysiloxanes are usually higher than those obtained with increased cyclodextrin content in a more polar polysiloxane, without the drawback of reduced column efficiency resulting from high cyclodextrin content. Changing the polarity of the polysiloxane can also be useful for limited “selectivity tuning” of the chiral stationary phases, for resolving randomly co‐eluting peaks.
Effects of pH and organic solvent on chromatographic behavior in capillary electrochromatography
Authors: Kitagawa Shinya , Tsuda Takao 
Published: May 2005

AbstractElectrochromatography is demonstrated using a 50 μm i.d. capillary column. The separation of solutes due to their different mobilities is obtained by the application of high voltage along the column. The elution times of solutes are dependent on the pH and composition of the eluent. Both electrophoretic and electroosmotic flow velocities are almost constant between 30 and 90% methanol in the eluent, and they increase with more than 90% methanol. The pH dependence of the electroosmotic flow velocity may be related to the dissociation of unreacted silanol groups on the surface of the ODS‐silica particles.
Electrogenerated chemiluminescence detection for capillary electrophoresis
Authors: Gilman S. Douglass , Silverman Charlotte E. , Ewing Andrew G. 
Published: May 2005

AbstractElectrogenerated chemiluminescence (ECL) detection based on the reaction of luminol and H2O2 has been developed for capillary electrophoresis. The ECL response at carbon fiber and platinum wire microelectrodes has been investigated. Carbon fiber electrodes are observed to be less sensitive than platinum electrodes but provide a more stable response. The ECL response at a carbon fiber electrode is linear over three orders of magnitude for luminol with a linear correlation coefficient of 0.998. Mass detection limits of 92 amol and 260 amol have been obtained for luminol using platinum wire microelectrodes and carbon fiber microelectrodes, respectively. The influence of hydrogen peroxide concentration (in the detection buffer resrvoir) on the luminescence response has been examined and found to be dependent on electrode type. The dependence of the ECL response on the applied voltage at the microelectrode has been studied for both electrode types. Capillary electrophoresis with ECL detection has been used for analysis of amines derivatized with N‐(4‐aminobutyl)‐N‐ethylisoluminol coupled to N, N‐disuccinimidylcarbonate (ABEI‐DSC). Detection limits of 2.0 fmol and 0.96 fmol are obtained for n‐octylamine and n‐propylamine, respectively. In addition, ABEI‐DSC has been used to successfully label the tripeptide Val‐Tyr‐Val, and micellar electrokinetic capillary chromatography has been used with ECL detection for the separation of ABEI‐DSC labeled amines.
Cyclodextrin PLOT columns for the gas‐solid chromatographic separation of light hydrocarbons and inorganic gases
Authors: Reid George L. , Armstrong Daniel W. 
Published: May 2005

AbstractAlpha and beta cyclodextrin (α‐ and β‐CD) were chemically bonded to porous layer fused silica open tubular columns and used as gas‐solid chromatographic (GSC) stationary phases for the separation of C1 to C6 hydrocarbons and a variety of inorganic gases. In general, these cyclodextrin PLOT columns were superior to the analogous packed columns. The capillary columns show similar selectivities with an increase in efficiency and number of theoretical plates over the packed columns. The cyclodextrin stationary phases show good selectivities toward the light hydrocarbons and inorganic gases on capillary columns as short as ten meters. Subambient temperatures allow the baseline resolution of oxygen from nitrogen. These columns have been effectively utilized at temperatures up to 260°C without loss of efficiency or degradation of selectivity.
Reversed‐phase liquid chromatography coupled on‐line with capillary gas chromatography II. Use of a solvent vapor exit to increase introduction volumes and introduction rates into the gas chromatograph
Authors: Goosens Elise C. , de Jong Dirk , de Jong Gerhardus J. , Th. Brinkman Udo A. 
Published: May 2005

AbstractA large‐volume introduction system for capillary gas chromatography (GC) is described which can be coupled on‐line with reversed‐phase liquid chromatography (LC) using 2 mm i.d. LC columns. An on‐column interface with a special retention gap, coated with a very thin film (0.02 μm) of Carbowax was used. Insertion of a solvent vapor exit before the analytical gas chromatography column allowed the solvent evaporation rate for an azeotropic acetonitrile/water mixture (84:16, v/v) to increase from 20 to 175 μL min−1 at 91°C and 150 kPa inlet pressure. A volume of 200 μL of this mixture containing phenanthrene and the potential basic drug eltoprazine, could be injected into the retention gap at introduction rates up to 200 μL min−1, under partially concurrent solvent evaporation conditions. Repeatability (CV = 2.4%) and linearity (at least 10–1000 ng mL−1) were satisfactory. The Carbowax‐coated retention gap has a relatively large retention power for the polar solute. This means that the solvent can be completely evaporated through the vapor exit without loss of analyte. With apolar solutes, losses will occur if evaporation is unduly prolonged. In order to allow the use of a nitrogen‐phosphorus detector, a special pressure‐balanced carrier gas circuit was designed and tested for total solvent‐free performance of the detector. With this set‐up, 150 μL injections of eltoprazine in the acetonitrile/water azeotrope were made at an introduction rate of 200 μL min−1. No traces of acetonitrile were detected, while analyte detectability was 20‐fold higher than with the FID.Finally, the practicability of reversed‐phase LC‐GC was demonstrated by on‐line heart‐cutting of the phenanthrene‐containing fraction from a 2 mm i.d. LC column using acetonitrile/water (84:16, v/v) as eluent, and analyzing it by capillary GC‐FID.
New μLC/GC interface
Authors: Rusek Miroslav , Cigánková Marie , Krejčí Miloš , Kahle Vladislav 
Published: May 2005

AbstractThe combination of a microcolumn liquid chromatograph with a gas chromatograph is described. The new interface is based on the principle of pneumatic regulation of the effluent flow from the microcolumn chromatograph. In the course of operation, the analyte does not contact the metal components of the apparatus.
Preparation and evaluation of supercritical carbon dioxide‐packed capillary columns for HPLC and SFC
Authors: Tong Daixin , Bartle Keith D. , Clifford Anthony A. 
Published: May 2005

AbstractPreparation of packed capillary columns with supercritical carbon dioxide as the packing carrier is demonstrated; column performance was evaluated by both HPLC and SFC. It is shown that this procedure yields excellent column performance. The density of the packed bed can be controlled by varying the restrictor dimensions and the packing pressure. Column preparation using a supercritical fluid is more rapid than with liquid slurry packing and yields good column stability. Because supercritical fluids have a wider range of viscosities and velocities, in comparison with gases and liquids, a wide choice of packing conditions is available. Several applications of columns packed by this method are presented.
Chiral separations using packed capillary liquid chromatography
Authors: Cortes Hernan J. , Nicholson Lawrence W. 
Published: May 2005

AbstractReduction of the internal diameter of the column used for the separation of enantiomers by liquid chromatography to microcolumn dimensions (0.1‐0.5 mm i.d.) offers significant advantages to the technique, such as low eluent consumption, reduced packing material needs which ensures column‐to‐column reproducibility and lower column costs, and high efficiencies, among others. The present report documents studies conducted in the preparation of highly efficient microcolumns for chiral separations using Chiracel OD stationary phase (3,5‐dimethylphenylcarbamate derivative of cellulose). The resolution, efficiency, and peak asymmetry values obtained using microcolumns were significantly better when compared to a conventional size column (4.6 mm i.d.) of the same length (25 cm). These results may be explained by the more efficient column packing process when using fused silica tubing of narrow diameter as column material. The use of long (80 cm) microcolumns yielded increases in enantiomer resolution of 200–300%. Operation of the long microcolumns at high linear velocities resulted in resolution increases over conventional columns without a decrease in analysis time. In addition to much improved column performance, miniaturization of chiral separation systems has a significant economic impact. Since operating flow rates are 5 μL min−1 compared to 1–2 mL min−1 for conventional columns, a significant savings in the cost of solvents and solvent disposal can be realized by using the microcolumn technology. In addition, the small amount of packing material required to prepare a microcolumn significantly reduces column costs.
Scanning electrochemical detection in capillary electrophoresis
Authors: Ferris Sandra S. , Lou Guoan , Ewing Andrew G. 
Published: May 2005

AbstractScanning electrochemical detection has been combined with capillary electrophoresis to increase the resolving power for closely eluting solutes. This detection mode has been characterized and provides voltammetric information for easily oxidized solutes with linear detection over concentrations in the 10−3 to 10−5 M range. Detection limits for catechols range from 360 amol to 740 amol (2.3 μM to 6.6 μM concentrations). Finally, two neutral solutes, catechol and tryptophan, co‐elute under zone electrophoresis conditions, but are resolved with scanning detection.
Chitosan coated capillary with reversed electroosmotic flow in capillary electrophoresis for the separation of basic drugs and proteins
Authors: Sun Peng , Landman Adam , Hartwick Richard A. 
Published: May 2005

AbstractAn enhanced surface coating method was developed for capillary electrophoresis (CE) using the natural polymer chitosan. The cationic property of chitosan at pH below 6.5 created a reversed electroosmotic flow (EOF) in the capillary. The EOF changed significantly with the run buffer pH at values below 4.0, with less pH dependency at values in the pH range of 4.0‐5.5. The new coating exhibited good performance reproducibility. The relative standard deviation (RSD) of EOF was 0.77%. The EOF changed an average of 2.4% after 10 h normal use. The EOF started to change significantly after a constant electric field (300 v cm−1) had been applied for 20 h. This capillary with a reversed EOF can be used to reduce the solute‐wall interaction problem for separations of basic analytes, for example, separations of positively charged proteins and basic drug enantiomers.
Simple detector for microcolumn LC using electrospray ionization
Authors: Št́astná Miroslava , Krejčí Miloš , Kahle Vladislav 
Published: May 2005

AbstractA simple detector for microcolumn liquid chromatography using electrospray ionization is described. The principle operational parameters of the detector were evaluated. The minimum detectable quantity for a variety of analytes is in the 10−10 mole range or below.
Analytical merit of electrospray ion mobility spectrometry as a chromatographic detector
Authors: Chen Yong Hong , Hill Herbert H. , Wittmer Douglas P. 
Published: May 2005

AbstractElectrospray ionization ion mobility spectrometry (ESI‐IMS), a technique which has only recently become analytically useful, has been evaluated for use as a detector for microbore liquid chromatography and capillary electrophoresis. Figures of merit for ESI‐IMS were determined. Detection limits as low as 1 × 10−15 mol s−1 were measured, with a linear response range of 3 to 4 orders of magnitude and with reproducibility within 3% (relative standard deviation of peak area). Gradient elution with water/methanol mobile phase did not perturb chromatographic baseline, compound response, or product ion mobility. Both positive and negative ion mobility spectra for more than 30 compounds demonstrated the sensitivity of ESI‐IMS response to a wide range of analytes. Finally, the concept of using ESI‐IMS as an ionization source for gasphase samples was presented, potentially unifying detector application for both gas and liquid chromatography.
Self‐assembled alkylsilane monolayers for the preparation of stable and efficient coatings in capillary electrophoresis
Authors: Huang Mingxian , Dubrovcakova‐Schneiderman Eva , Novotny Milos V. , Fatunmbi Hafeez O. , Wirth Mary J. 
Published: May 2005

AbstractThe approach of forming self‐assembled monolayers on the surface of fused silica capillaries has been evaluated for capillary electrophoresis of proteins. Two polymer matrices (polymerized acrylamide or methacryloyl‐Tris) were successfully grafted on the self‐assembled monolayers, as evidenced by electroosmotic flow measurements and efficient separations of model proteins.
Gas chromatography‐atomic emission detection (GC‐AED) set‐up for bio‐monitoring of PCBs and methylsulfonyl‐PCBs
Authors: Janák Karel , Grimvall Eva , Östman Conny , Colmsjö Anders , Athanasiadou Maria , Bergman Åke 
Published: May 2005

AbstractGas chromatography‐atomic emission detection (GC‐AED) has been evaluated in order to determine the optimal conditions for chlorine and sulfur response of chlorinated biphenyls (CBs) and methylsulfonyl metabolites of CBs (MeSO2‐CBs). The influence of the shape of the capillary column end facing the plasma, make‐up gas flow, additional transfer line make‐up gas flow and reagent gas flows on the detector response has been studied. Using an additional make‐up gas flow applied through a transfer line capillary having a decreased outlet diameter yielded an increased detector response with minimum detectable levels for sulfur and chlorine of 1.7 and 20 pg, respectively. Further, a substantial decrease in peak tailing was achieved. The applicability of the method for analysis of biological materials is demonstrated by the determination of the main CB congeners present in human blood and of MeSO2‐CBs in seal blubber.
Determination of trace quantities of volatile sulfur compounds in aqueous solutions by gas chromatography after purge and trap isolation and cryogenic focusing
Authors: Wardencki Waldemar 
Published: May 2005

AbstractA method for the determination of volatile organic sulfur compounds, such as dimethylsulfide (DMS), at the nanogram level in aqueous samples is described. A purge and trap technique was used to remove and preconcentrate DMS and other sulfur compounds from aqueous solutions. Trapping of the isolated compound was performed on Tenax TA and Carbosieve III S. The water vapor from the purging stream was removed by a commercially available Nafion tube inserted in a plastic container packed with molecular sieve 5A. Analytes, after thermal desorption, were recollected in a short fused silica capillary tube cooled with the vapors of liquid nitrogen to a temperature ca. −150°C. Next, sulfur compounds were revolatilized and directly transferred to the analytical capillary column for analysis. Detection was performed with a flame photometric detector. The whole procedure was optimized and checked using a homemade valving device easily coupled to any gas chromatograph. The method has been used to measure DMS and other volatile sulfur compounds in seawater of the Baltic Sea and in samples of water from three rivers in the Gdańsk, Poland, region.