bluuebunny/crossref_metadata_2025_split huggingface dataset:
Detection and sequence analysis of tryptic peptides by microcolumn liquid chromatography‐tandem mass spectrometry using an electrospray interface
Authors: Hail Mark , Lewis Sydell , Jardine Ian , Liu Jinping , Novotny Milos 
Published: May 2005

AbstractFused‐silica packed LC capillaries were interfaced with a triple quadrupole mass spectrometer through the electrospray ionization device. The coupling of these powerful techniques is suitable for structural characterization of constituents of peptide maps generated at high sensitivity. Sequence determinations appear possible at the femtomole level following this approach.
Microanalysis of explosives and propellants by on‐line supercritical fluid extraction/chromatography with triple detection
Authors: Munder Albrecht , Christensen Richard G. , Wise Stephen A. 
Published: May 2005

AbstractA compact analytical instrument is described which allows microsamples to be extracted with supercritical fluids, and the extract preconcentrated and analyzed by capillary supercritical fluid chromatography in a single coupled unit. Thus, no off‐line sample pretreatment is required, and the possibility of extraneous contamination is reduced. To achieve greater selectivity and sensitivity for selected species, three different detectors (UV absorption, flame ionization and electron capture) were all connected on‐line. This analytical instrument configuration was established by upgrading a commercial capillary supercritical fluid chromatograph using regular chromatographic supplies. To illustrate the analytical utility of this hyphenated technique, an assortment of compounds that are not easily determined by traditional gas chromatographic or liquid chromatographic methods was selected: explosives, propellants, and related species. The instrumental design, as well as selected analytical conditions (sample pretreatment, extraction, preconcentration, separation, and detection) were investigated to improve selectivity and/or sensitivity. The determination of explosive residues on soil is described as an environmental analysis application of the system. Detection limits for some compounds are estimated to be as low as 100 pg. The firearm propellants were characterized through their extractable organic constituents, and the usefulness of such characterization in forensic investigations is discussed. Closely related to this issue is the analysis of the residue in expended cartridge cases. A chromatographic fingerprint was obtained from the propellant used in the ammunition. This fingerprint can be used under certain circumstances to correlate a specific batch of propellant with the residue left in a fired cartridge case.
Preparation of polyacrylamide gel‐filled capillaries for capillary electrophoresis
Authors: Dolnik Vladislav , Cobb Kelly A. , Novotny Milos 
Published: May 2005

AbstractA procedure for preparing polyacrylamide gel‐filled capillaries, for use in capillary gel electrophoresis, is decribed. The method involves the principle of isotachophoretic polymerization, in which the polymerization initiator is introduced by electromigration to promote gradual polymerization of the acrylamide in a sequential manner along the length of the capillary. This procedure has been found to be superior to other methods for polymerizing gels inside of small‐bore (i.e., 50‐μm i.d.) capillaries, because of the reduced formation of bubbles in the gels during polymerization. The method described is simple, reproducible, and several capillaries can be prepared simultaneously. A preliminary result showing the use of 50‐μm i. d. gel‐filled capillaries for SDS‐polyacrylamide gel electrophoresis of proteins is shown.
Diffusion and thermodynamic measurements by supercritical fluid chromatography
Authors: Roth Michal 
Published: May 2005

AbstractApplications of supercritical fluid chromatography (SFC) to physicochemical measurements are reviewed. Emphasis is laid on the determination of binary diffusion coefficients at infinite dilution of solutes in supercritical solvents, and on actual or potential applications of SFC to the measurements of thermodynamic quantities in dilute, binary, supercritical mixtures. Physicochemical measurements emerge as a specific application field of SFC with many links to transport phenomena and to molecular thermodynamics of fluid‐phase equilibria.
Application of sample stacking to gravity injection in capillary electrophoresis
Authors: Burgi Dean S. , Chien Ring‐Ling 
Published: May 2005

AbstractSample stacking can be used to increase the amount of analyte loaded onto a capillary column without loss in resolution. After the sample is loaded onto the column, the analytes are then separated by conventional capillary zone electrophoresis. When using gravity injection, over an order of magnitude improvement in detection limit is achieved. There is an optimal point for the amount of material which can be injected onto the column based on the resolution desired for the separation.
Diffusion coefficients of oligonucleotides in capillary gel electrophoresis
Authors: Yin Hong‐Feng , Kleemiß Maria Helen , Lux Jürgen Alfred , Schomburg Gerhard 
Published: May 2005

AbstractDiffusion coefficients of oligonucleotides have been measured in polyacrylamide gel capillaries without application of an electrical field. A relationship between such diffusion coefficients and molecular size of the oligonucleotides could be achieved. The slower diffusion of larger oligonucleotides cannot explain the high separation efficiencies of capillary gel electrophoretic separations alone. By theoretical considerations it became obvious that diffusion coefficients of oligonucleotide molecules and also their intermolecular interaction with the polyacrylamide gel may be considerably changed by application of electrical fields.
Predictability and effect of phase behavior of CO2/propylene carbonate in supercritical fluid chromatography
Authors: Page Steven H. , Raynie Douglas E. , Goates Steven R. , Lee Milton L. , Dixon David J. , Johnston Keith P. 
Published: May 2005

AbstractThe phase behavior (P‐T‐x) of propylene carbonate was studied using a variable volume view cell for the regions applicable to supercritical fluid chromatography (SFC) and extraction (SFE). Type 5 phase behavior was observed. Phase separation was shown to significantly alter retention and selectivity in the analysis of coal extracts by capillary SFC. Propylene carbonate was found to have limited use as a modifier in capillary SFC. With 5.1 mol% propylene carbonate at 60°C, a single phase is maintained only at pressures above 250 atm.Twenty‐two methods used to estimate critical pressure (Pc), twenty‐seven methods used to estimate critical temperature (Tc), and thirty methods used to estimate critical volume (Vc) were evaluated for various modifiers employed in supercritical fluid chromatography (SFC). None of the methods could predict Pc, Tc, or Vc to within a 5% relative error for all of the modifiers tested. However, several of the methods were successful in predicting Pc, Tc, or Vc to within 5% for select chemical classes of compounds.Four methods used to estimate the vapor‐liquid critical loci of binary mixtures not only failed to accurately predict vapor‐liquid separation, but failed to predict the type of phase separation occurring. None of the above methods could reliably estimate the critrical parameters of propylene carbonate or the critical parameters of the mixture.
Determination of toluene diisocyanate in air using micro liquid chromatography with UV‐detection
Authors: Brunmark Per , Dalene Marianne , Sangö Carsten , Skarping Gunnar , Erlandsson Per , Dewaele Chris 
Published: May 2005

AbstractA routine method using micro‐LC for the determination of toluene diisocyanate (TDI) in air is presented. Air is sampled in impingers containing a toluene solution of 9‐(N‐methylaminomethyl)anthracene as derivatization reagent. The samples are evaporated to complete the reaction, dissolved in toluene, and shaken with buffer to remove access reagent. They are finally evaporated again, dissolved in acetonitrile/aqueous triethylamine phosphate solution and analyzed with micro‐LC. The LC‐system, except for the column and detector, consisted of conventional LC components. The concentration range investigated, 10–50 ng mL−1, gave correlation coefficients of 0.995 for the 2,6‐TDI isomer and 0.998 for the 2,4‐TDI isomer. The relative standard deviation for the method was 3.3% for 2,6‐TDI and 1.5% for 2,4‐TDI when analyzing solutions containing 10 ng mL−1 2,6‐TDI and 20 ng mL−1 2,4‐TDI (n = 15). Injection volumes of up to 200 μL gave a linear peak area response. The detection limits calculated for three times the chromatographic noise were 0.15 ng mL−1 for both TDI isomers when injecting 100 μL from a 1‐mL sample. This corresponds to 0.03 μg m−3 with 1 L min−1 air flow through the impinger for 5 min. The detection limits were found to be better than a factor of ten lower compared to conventional LC.
Influence of derivatization on the chiral selectivity of cyclodextrins: Alkylated/acylated cyclodextrins and γ‐/δ‐lactones as an example
Authors: Schmarr Hans‐George , Mosandl Armin , Kaunzinger Astrid 
Published: May 2005

AbstractSelectively alkylated and acylated cyclodextrin derivatives are suitable stationary phases for capillary GC. To obtain a closer insight into the separation mechanism, an inverse substituted cyclodextrin derivative was synthesized and characterized, and its chiral selectivity was compared with a traditionally substituted and characterized cyclodextrin. The influence of a polar group in the cyclodextrin molecule on the enantioselectivity for γ‐/δ‐lactones is shown with a new, diacylated, cyclodextrin derivative.
Boiling range distribution of petroleum and coal‐derived heavy ends by supercritical fluid chromatography
Authors: Raynie Douglas E. , Markides Karin E. , Lee Milton L. 
Published: May 2005

AbstractAlternatives to conventional gas chromatographic simulated distillation methods for high boiling materials are reviewed. Operational parameters for the use of supercritical fluid chromatography for simulated distillation are explored and examples for the analysis of both petroleum and coal‐derived samples are compared to conventional gas chromatographic methods and thermogravimetric analysis. Extension of the boiling range determined by simulated distillation to over 800°C is demonstrated. An n‐ octylpolysiloxane stationary phase minimized the aliphatic versus aromatic boiling point discrepancy common to other chromatographic methods.
Influence of pressure on solute retention in liquid chromatography
Authors: McGuffin Victoria L. , Evans Christine E. 
Published: May 2005

AbstractAlthough the mobile phase is generally considered to be incompressible in liquid chromatography, the local pressure appears to have a significant effect upon solute retention. In this investigation, laser fluorescence detection was utilized to measure solute retention directly along a reversed‐phase packed capillary column with a methanol mobile phase. For derivatized fatty acids, n‐C10:0 to n‐C20:0, the capacity factors increased systematically by +9.3% to + 24.4% under normal operating pressure conditions (1,500 to 5,000 psi). Whereas the magnitude of this increase in solute retention seems surprising, it appears to correlate well with the unified theoretical model developed by Martire.
Volatile oil analysis of Thymus vulgaris L. by directly coupled SFE/GC
Authors: Hartonen Kari , Jussila Matti , Manninen Pekka , Riekkola Marja‐Liisa 
Published: May 2005

AbstractDynamic supercritical fluid extraction (SFE) with CO2 as the supercritical fluid was coupled to capillary gas chromatography (GC). A cryotrap/thermal desorption unit external to the GC was used to collect the extracted compounds and introduce them into the GC column. The reproducibility of the SFE/GC system was tested through replicate analyses of thyme, and the recoveries of thyme components were compared with those obtained from hydrodistilled oil of thyme by GC. Excellent agreement was achieved, but the results showed that chromatographic valves and valve materials may be critical in obtaining good results.
Indirect UV photometric detection in capillary zone electrophoresis for the determination of phytate in soybeans
Authors: Nardi Annalisa , Cristalli Michele , Desiderio Claudia , Ossicini Luigia , Shukla Shyama Kant , Fanali Salvatore 
Published: May 2005

AbstractA rapid and simple analytical method was developed to determine phytate anion in soybeans. The analysis was performed by capillary zone electrophoresis with indirect UV photometric detection. The determination of phytate was carried out with a background electrolyte in which benzoate was the absorbing ion at 254 nm.
Influence of coiling on performance in capillary electrophoresis using open tubular and polymer network columns
Authors: Wicar Stanislav , Vilenchik Masha , Belenkii Alexii , Cohen Aharon S. , Karger Barry L. 
Published: May 2005

AbstractThe influence of coiling on column efficiency in capillary electrophoresis (CE) has been examined. In open tubular columns of 75‐μm i.d., no significant effect of column coiling on efficiency was observed, even at plate counts of 2 × 106 m−1. The small column internal diameter and radial diffusion in free solution was able to minimize the potential deleterious effect of coiling. With gel‐filled columns of very high efficiency (˜107 plates m−1), the influence of coiling on column efficiency was, however, significant, e.g., a factor of 3 or more loss in plate count per coil. For relatively rigid gels (e.g., 9% T linear polyacrylamide with 7 M urea), this observed loss of column efficiency was attributed mainly to the inability of the polymer network to permit diffusional relaxation of the coiling effects. A significant influence of coiling on column efficiency was also found with medium concentration polymer networks (e.g., 3‐6% T linear polyacrylamide with no urea). The polymer network structure was assumed to change under the influence of mechanical stress caused by coiling, resulting in anisotropy across the column. Furthermore, the changes in structure and in efficiency were found to be time dependent and, in general, reversible. The effect appears to be caused by the shear force imposed on a polymer network structure, since changes are only observed when the column shape is altered after the polymer has been loaded into the capillary.
Packed capillary liquid chromatography/electrospray ionization/mass spectrometry in the pharmaceutical sciences: Characterization of protein mixtures
Authors: Moseley M. Arthur , Unger Steve E. 
Published: May 2005

AbstractThe coupling of packed capillary liquid chromatography with electrospray ionization mass spectrometry has yielded an instrument capable of generating molecular weight information from very complex natural protein mixtures. The use of the packed capillary liquid chromatography columns offers two principle advantages over conventional liquid chromatography columns: high separation efficiencies and very low mobile phase flow rates (100 nL min−1). The low mobile phase flow rates permit the use of a relatively high ionic strength buffer (0.1% trifluoroacetic acid), While delivering a very low mass flux of the buffer to the mass spectrometer.
Syntheses of isomeric cyanobiphenyl‐substituted polysiloxanes for stationary phases in gas chromatography
Authors: Rossiter Bryant E. , Reese Shawn L. , Morgan Sarah , Malik Abdul , Bradshaw Jerald S. , Lee Milton L. 
Published: May 2005

AbstractNine isomeric cyanobiphenyl‐substituted polysiloxanes were synthesized using a four‐step procedure and tested as stationary phases in open tubular column gas chromatography.
Novel cyanobiphenylpolysiloxane stationary phases for gas and supercritical fluid chromatography
Authors: Malik Abdul , Ostrovsky Ivan , Sumpter Sheldon R. , Reese Shawn L. , Morgan Sarah , Rossiter Bryant E. , Bradshaw Jerald S. , Lee Milton L. 
Published: May 2005

AbstractNine different 25% cyanobiphenyl‐substituted polysiloxane (CBP) stationary phases were evaluated for use in gas and supercritical fluid chromatography. They were easily coated and cross‐linked on fused silica capillaries to produce highly efficient columns. For a 200 μm i.d. column, an efficiency of as high as 5,100 plates m−1 was obtained. For most of the new phases, the upper temperature limit was 300°C. A comparative study of the chromatographic behaviors of the cyanobiphenyl and commercial reference phases was made. Some of the cyanobiphenyl stationary phases showed polarities higher than those for carbowax 20M or 50% cyanopropyl. All six positional isomers of dodecylxylene and the five isomers of four‐ring polycyclic aromatic hydrocarbons were baseline resolved on GC capillary columns with certain of the cyanobiphenyl phases, demonstrating higher selectivity over SE‐54 or Carbowax 20M phases. In SFC, a cyanobiphenyl column provided better separation of a standard coal tar sample than columns with biphenyl or cyanopropyl phases. The retention behavior of fatty acid methyl esters and a mixture of polar solutes was investigated on the cyanobiphenyl and references phases. With respect to certain solute pairs, the selectivities of the new stationary phases were found to increase with temperature. The new cyanobiphenyl phases were found to be useful for GC and SFC separations of various classes of complex mixtures including essential oils, explosives, and polycyclic aromatic hydrocarbons.
Direct examination of separation processes in liquid chromatography: Effect of temperature and pressure on solute retention
Authors: McGuffin Victoria L. , Evans Christine E. , Chen Shu‐Hui 
Published: May 2005

AbstractIn this study, retention processes in reversed‐phase liquid chromatography were examined in situ along an optically transparent column by means of laser‐induced fluorescence. Using a homologous series of derivatized fatty acids as model solutes, the capacity factors were systematically measured as a function of temperature in the range from 10 to 60°C and pressure in the range from 980 to 4,430 psi. A phase transition was observed for the octadecylsilica stationary phase as temperature was decreased and as pressure was increased. From evaluation of its thermodynamic properties during this phase transition, the stationary phase appears to be more similar to a randomly oriented alkane solvent than a highly ordered system such as a phospholipid membrane. Because this phase transition occurs within the range of routine operating conditions in liquid chromatography, it has important implications for both fundamental and practical applications.
Solventless injection technique for microcolumn separations
Authors: Arthur Catherine L. , Chai Meng , Pawliszyn Janusz 
Published: May 2005

AbstractThermal desorption of analytes from a solid phase microextraction (SPME) device is the ideal techniques for sample introduction into microcolumns because the solvent is entirely eliminated. SPME is compatible with various injector designs, is independent of the instrument manufacturer, and can be completely automated. It can be used to concentrate the analytes from liquid, gaseous, or headspace samples with equal success. The location of the fiber in the injector for programmable direct and splitsplitless injectors are described since fiber positioning varies with injector design. An SPME injection consists of two parts: desorption in the injector followed by cryofocusing in the gas chromatographic column. The factors affecting desorption and cryofocusing, and the thickness of the column stationary phase. Example of fiber injections of liquid and gaseous samples are discussed.
Reduced elution speed detection for capillary electrophoresis/mass spectrometry
Authors: Goodlett David R. , Wahl Jon H. , Udseth Harold R. , Smith Richard D. 
Published: May 2005

AbstractA combined capillary electrophoresis/mass spectrometry (CE/MS) method is described that provides an increase in the efficiency of analysis by decreasing the analyte elution rate into an electrospray ionization (ESI) interface. The method is readily implemented by instituting a step change in the CE electric field strength for desired periods of time during a separation. As a result, the m/z range or the number of times an m/z range can be scanned while a solute elutes is increased by a factor proportional to the decrease in CE electric field strength. In addition, the method is shown not to cause any significant loss in separation quality as demonstrated for mixtures of proteins and peptides, while providing an effective gain in sensitivity. This allows an enhancement in the quality of mass spectra recorded while scanning wide m/z ranges. Mass spectra for a set of standard proteins were obtained for injections of 60 femtomole/protein, while analysis of an albumin tryptic digest was obtained for injections corresponding to 40 femtomoles of protein.
Separation of nucleosides and nucleotide‐3′‐monophosphates by micellar electrokinetic capillary chromatography
Authors: Lecoq Anna‐Francesca , Montanarella Luca , Biase Sebastiano Di 
Published: May 2005

AbstractSimultaneous separation of ionic and neutral compounds in micellar electrokinetic capillary chromatography (MECC) is a consequence of a combination of charge/mass ratios, hydrophobicity and charge interactions at the surface of the micelles. The type of resolution can be chosen mainly by modification of the buffer composition and pH. Reproducibility depends on the capillary tubing characteristics, operating conditions, and temperature effects. We report here on the different buffer compositions, pH, temperature, operating conditions, and capillary tubing treatments for the optimal separation and best reproducibility of deoxynucleosides and deoxynucleotide‐3′‐monophosphates. The effects of different buffer compositions were tested when operating in a constant current mode at 38 μAmps. Lithium phosphate buffer improved the separation speed with little loss in resolution. The best concentration was found to be 20 mM. A concentration of 5% acetonitrile substantially improved the efficiency of the nucleoside peaks and therefore their resolution. The optimum SDS concentration was found to be at 100 mM. The pH has a significant influence on retention time and resolution, and was adjusted for maximum resolution at pH 9.6. Capillary surface treatments were also investigated. Effective heat dissipation occurred below an operating voltage of 15kV, and a temperature of 35°C was found to give a good compromise between efficiency, resolution, and time of analysis. Time of analysis can be decreased by using higher operating voltages without compromising the resolution. Efficiencies were 350,000 and 235,000 plates m−1 for the nucleosides and nucleotides, respectively. The reproducibility of retention times was good with coefficients of variation below 1%, which allows the possibility for automatic fraction collection.
tert‐Butyldimethylsilyl‐substituted cyclodextrin derivatives as versatile chiral stationary phases in capillary GC
Authors: Maas Birgit , Dietrich Armin , Karl Volker , Kaunzinger Astrid , Lehmann Detmar , Köpke Thomas , Mosandl Armin 
Published: May 2005

Abstracttert‐Butyldimethylsilylated cyclodextrin derivatives dissolved in polysiloxanes were shown to be versatile chiral stationary phases for the differentiation of important chiral food and flavor ingredients and chiral acids of biochemical and pharmaceutical interest.