bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of methanol/water mobile phase on the properties of immobilized Carbowax 20M stationary phase
Authors: Horká Marie , Janák Karel , Krejčí Miloš 
Published: May 2005

AbstractCapillary columns with immobilized Carbowax 20M based on polyurethane (25.6‐μm i.d., 0.06‐μm df, 2.5–4‐m length, and water/methanol mobile phase) were used in capillary liquid chromatography. Stationary phase film swelling occurs due to the effects of the water/methanol mobile phase. The degree of swelling ranges from 0 to 50%. Owing to the resistance to mass transfer decreases, which improves the operation in capillary columns of this type even at temperatures below that of glass transition. The diffusion coefficients in the stationary phase measured by open tubular column liquid chromatography are comparable with those measured by gas chromatography. They range from 10−4 to 10−6 mm2 s−1.
Evaluation of etched borosilicate glass capillary columns in reversed phase open tubular liquid chromatography
Authors: Dohmeier Daniel M. , Jorgenson James W. 
Published: May 2005

AbstractThe performance of etched borosilicate capillary columns with a bonded octadecyl stationary phase has been examined. Plate heights for three test compounds in columns with inner diameters between 6.5 and 14.6 μm were measured as a function of mobile phase velocity. The reduced plate height vs. reduced velocity curves were then fit to the Golay equation using nonlinear regression analysis. It was found that in addition to longitudinal diffusion in the mobile phase, longitudinal diffusion in the stationary phase was a significant contributor to broadening at low mobile phase flow rates. At higher flow rates, resistance to mass transfer in the stagnant mobile phase in the porous glass produced by the etching procedure became measurable.
Nitrogen‐selective detection in capillary supercritical fluid chromatography of derivatized oligosaccharides
Authors: Shirota Osamu , Liu Jinping , Novotny Milos 
Published: May 2005

AbstractMethoximation of reducing oligosaccharides, combined with the additional derivatization of hydroxy groups, yields derivatives suitable for capillary supercritical fluid chromatography with thermionic detection. Detection limits on the order of picogram‐per‐second can easily be achieved. The utility of this analytical procedure has been verified by the analysis of the carbohydrate content of chicken trypsin inhibitor.
Unified open tubular column chromatography: Sequential gas chromatography, at normal pressures, and supercritical fluid chromatography on the same column
Authors: Robinson Robert E. , Tong Daixin , Moulder Robert , Bartle Keith D. , Clifford Anthony A. 
Published: May 2005

AbstractA unified chromatograph was constructed in which open tubular column gas chromatography, at normal helium carrier gas pressures, followed by supercritical fluid chromatography with carbon dioxide mobile phase was carried out in a single run using a 100‐μm i. d. column. Sample introduction was accomplished by means of a pneumatically‐actuated rotary injection valve. A second rotary valve was used post‐column to direct the flow of column effluent to the flame ionization detector through an uncoated fused silica restrictor during the GC separation mode or to the FID through a frit restrictor during the SFC separation mode. This novel valve switching arrangement allowed system operating parameters of temperature and pressure programs and linear velocities to be optimized independently of each separation mode. The unified GC/SFC system was demonstrated for practical applications in various fields of process and product quality control.
Examination of the properties of different 20% phenyl‐substituted polymethylsiloxane stationary phases for capillary chromatography
Authors: Hägglund Ingela , Blomberg Lars , Janàk Karel , Claude Saturnin , Tabacchi Raffaele 
Published: May 2005

AbstractThree polysiloxanes, each having 20% phenyl substitution, have been evaluated for use as stationary phases in fused silica open tubular columns for gas and supercritical fluid chromatography. The columns were coated with PS–090 which had been treated in an aluminum pan in order to improve immobilization properties, OV‐7, and a newly synthesized phase, Polymer S.Excellent columns were prepared with PS‐090; however, treatment in the aluminum pan was an uncontrolled process, and the reproducibility of polarity may be questioned. For comparison, OV‐7 could not be immobilized, but columns coated with this phase showed good thermal stability. The silanol terminated Polymer S was immobilized via a mechanism involving scission of phenyl groups; thus polarity was decreased after immobilization. However, columns for which Polymer S was immobilized in the presence of a cross‐linking reagent maintained their polarity. Such columns showed very good chromatographic performance. These columns were applied to the separation of polynuclear aromatic compounds by GC and to the analysis of extracts from a thermomechanical pulping white water and lichen by SFC.
Solute focusing in supercritical fluid chromatography
Authors: Koski Iina J. , Lee Milton L. 
Published: May 2005

AbstractSolute focusing is an important topic in chromatography, but it has not been discussed extensively in the recent supercritical fluid chromatography literature. The purpose of this paper is to review the different methods that have been used to focus solutes in supercritical fluid chromatography. The theoretical basis for phase ratio and partition coefficient focusing is described. Different solute focusing devices that are used in on‐line supercritical fluid extraction and chromatography are shown. The methods and principles of removing the solvent from the solutes prior to the analytical column, and hence reducing band broadening in the column due to the solvent, are discussed in context with the use of a retention gap or a mixing chamber, and in solvent vent injection.
Capillary electrophoresis with surface coated capillaries
Authors: Kohr Joerg , Engelhardt Heinz 
Published: May 2005

AbstractWith uncoated fused silica capillaries, the electroosmotic flow and its contribution to solute migration are in part responsible for problems with the reproducibility of migration time due to hysteresis effects. In transferring coating procedures from silica to capillary surfaces, it has been possible to prepare stable polymeric coatings where hysteresis effects are negligible. Acrylamide coatings reduce the electroosmotic flow. A pH independent flow could be achieved with bonded cation exchange groups. With bonded anion exchangers, reversal of electroosmotic flow is possible.
Narrow (5‐50‐μm i.d.) open tubular columns in liquid chromatography using immobilized polymethyloctadecylsiloxane as stationary phase
Authors: Göhlin Karin , Larsson Marita 
Published: May 2005

AbstractThis paper presents in detail the preparation of highly efficient, stable open tubular (OT) columns for reversed‐phase liquid chromatography. Chromatographic properties of 5‐50‐μm i.d. fused silica columns (1.5‐5 m in length) are described, and details of the coating procedure are discussed. On‐column fluorescence detection was used for the model substituted‐anthracene test solutes. Gas chromatography was used as a complementary technique for column characterization.The stationary phase studied, immobilized polymethyloctadecylsiloxane, PMSC18, was chosen because of its more lipophilic character compared to other siloxanes. As expected, a higher retention power was found compared to polydimethylsiloxane coatings.The polymeric stationary phase showed good properties. More than 900,000 plates were achieved in 25 min (k = 0.1) in a 5‐μm i.d. fused silica OT column. The stationary phase contribution to band broadening was less than 10% in an 11‐μm i.d. column at a flow rate thirty times uopt (k = 1.3).
Fabrication and characterization of a silicon microvalve
Authors: Emmer Åsa , Jansson Mårten , Roeraade Johan , Lindberg Ulf , Hök Bertil 
Published: May 2005

AbstractThe fabrication of a unidirectional micro‐valve in silicon is reported. Pressure/flow characteristics between 0–1 bar for water were measured. Practically no leakage was observed (less than 1 nL min−1) when the valve was pressurized in the backward direction. A nonlinear pressure‐flow relation, believed to be due to the particular design of the closing cantilever beam, was observed in the forward direction. Some of the merits of the construction are discussed.
Enantiomer separation by capillary SFC and GC on immobilized permethyl‐β‐cyclodextrin: A systematic comparison
Authors: Schmalzing Dieter , Nicholson Graeme J. , Jung Martin , Schurig Volker 
Published: May 2005

AbstractImmobilized permethyl‐β‐cyclodextrin was used for enantiomer separation by capillary supercritical fluid chromatography and gas chromatography. The influences of pressure and temperature on chiral separation factors, α, and capacity factors, k, have been studied for four representative racemic solutes. The enantioselectivities in supercritical fluid chromatography and gas chromatography are compared. Solvation effects by supercritical carbon dioxide are discussed.
Quantitative polymer additive analysis by multidimensional chromatography using on‐line coupled microcolumn size exclusion chromatography as a preliminary separation
Authors: Cortes Hernan J. , Bormett Gary E. , Graham Jeffrey D. 
Published: May 2005

AbstractThe quantitative determination of polymer additives using a multidimensional system consisting of microcolumn size exclusion chromatography (micro SEC) coupled on‐line to a capillary gas chromatograph and to a conventional size LC system is described. The results obtained were compared to conventional sample preparation procedures consisting of dissolution of the polymer followed by precipitation and analysis of the supernatant. Results obtained for two polymer systems studied indicated losses for some additives using the precipitation approach.An on‐line coupled micro‐SEC‐LC system was investigated for the separation of compounds in which the volatility may not allow determination via capillary GC. The lower volumetric dispersion given by the microcolumns allowed introduction of the complete additive fraction without detrimental effects on the peak shape or resolution.
Effects of different mobile phases on immobilized carbowax 20M stationary phase in capillary liquid chromatography
Authors: Horká Marie , Krejčí Miloš , Kahle Vladislav 
Published: May 2005

AbstractPolyurethane immobilized Carbowax 20M stationary phase was used in capillary liquid chromatography. Mobile phases tested in this study (distilled water and aqueous solutions of the following solvents: 5.5% methanol, 5% acetone, 5, 10, 20% acetonitrile, 0.815% chloroform, 0.178% benzene and up to 0.00095% hexane) cause considerable swelling of the stationary phase polymeric film. The stationary phase swelling index reached a maximal value of S = 131. Diffusion coefficients in the stationary phase vary between 2.6 × 10−5 and 6.5 × 10−4 mm2 s−1.
Determination of naproxen in serum by capillary electrophoresis with ultraviolet absorbance and laser‐induced fluorescence detection
Authors: Soini Helena , Novotny Milos V. , Riekkola Marja‐Liisa 
Published: May 2005

AbstractMethodology for quantitative determination of an anti‐inflammatory drug, naproxen, in human serum by capillary electrophoresis (CE) is described. Ultraviolet absorbance (UV) and laser‐induced fluorescence (LIF) detection without derivatization procedures have been applied in two concentration ranges: the UV absorbance detection method is applicable in the concentration range of 0.5 ‐ 25 μg mL−1 (2 μM – 100 μM), permitting pharmacokinetic studies after a single oral dose of naproxen; for the lower concentration range of 0.01 – 0.5 μg mL−1 (40 nM ‐ 2 μM), LIF detection has been utilized. Sample preparation includes a simple liquid‐liquid extraction of 1.0 mL (UV) or 0.25 mL (LIF) serum aliquots. After solvent evaporation, redissolved samples were analyzed using Tris‐Tricine buffer. UV absorbance measurement was set at 254 nm. LIF using the helium‐cadmium (He‐Cd) laser as a source (excitation at 325 nm) was measured at 375 nm due to the native fluorescence of naproxen. Both methods provided interference‐free, linear and highly precise results. At the quantitation limit, 0.1‐pmol (UV) and 3‐fmol (LIF) naproxen levels were detected. Using ketoprofen (UV) and warfarin (LIF) as internal standards, analytical precision improved substantially.
Cu‐phthalocyanine stationary phase in microcolumn liquid chromatography
Authors: Jinno Kiyokatsu , Uemura Takashi , Haginaka Jun , Saito Yutaka 
Published: May 2005

AbstractIn this investigation, liquid chromatography using Cu‐phthalocyanine stationary phases were examined for polycyclic aromatic hydrocarbon (PAH) analyses. The results have indicated that Cu‐phthalocyanine phases can be useful for PAH separations by their planarity recognition capabilities.
Programmed‐temperature injector for large‐volume sample introduction in capillary gas chromatography and for liquid chromatography‐gas chromatography interfacing
Authors: Staniewski Jacek , Janssen Hans‐Gerd , Cramers Carel A. , Rijks Jacques A. 
Published: May 2005

AbstractThe introduction of large sample volumes in capillary gas chromatography is becoming increasingly important in various application areas. Especially in the analysis of very dilute sample (e.g., environmental samples) and in coupled LC‐GC, large volume sampling is extremely important. Programmed‐temperature sample introduction is shown to be an attractive technique for these purposes.In this paper we present some applications of large volume sampling in environmental analysis. Water samples were analyzed using both off‐line and on‐line extraction with gas chromatography (GC) analysis. In the off‐line method, pollutants were extracted into hexane or methylene chloride. Using the programmed‐temperature injector, up to 250 μL of the extract could be introduced into the GC system. In this way, reproducible quantitative analysis of PAHs and herbicides were achieved at sub‐ppb concentrations using flame ionization detection. In the on‐line mode, pollutants were preconcentrated on a short liquid chromatography (LC) column packed with a PLRP‐S solid phase extraction material. After the trapping step, the components were desorbed by ethyl acetate and transferred directly into the programmed‐temperature vaporizer (PTV‐GC) system. Using this method, detection limits below about 1 ppb of herbicides in water were obtained.
Preparation of polyacrylamide gel‐filled capillaries by photopolymerization for capillary electrophoresis
Authors: Bruin Gerard J. M. , Wang Tianlin , Xu Xiaoma , Kraak Johan C. , Poppe Hans 
Published: May 2005

AbstractA new preparation method for polyacrylamide gels in fused silica capillaries is described. In this method use is made of riboflavin as a light sensitive initiator for the polymerization reaction. Also, results from measurements on the diffusion coefficients of four oligonucleotides in a polyacrylamide gel are reported. Furthermore, a new preparative method to purify and collect oligonucleotides is presented. Separation performance of the gels was tested with various samples of oligonucleotides.
Verification of nonproduction of chemical warfare agents: I. Determination of organophosphorus compounds by microcolumn liquid chromatography with flame photometric or thermionic detection
Authors: Kientz Charles E. , Verweij Albert , De Jong Gerhardus J. , Th. Brinkman Udo A. 
Published: May 2005

AbstractMicrocolumn liquid chromatography (micro‐LC) with on‐line flame photometric (FPD) or thermionic detection (TID) has been used for the determination of a series of organophosphoric and organophosphonic acids isolated from various sample matrices. Silica‐based ion‐exchange materials and polymer packings have been used as stationary phases. In order to improve the sensitivity (expressed in concentration units) of the technique, trace enrichment via a miniaturized precolumn (4 mm × 1 mm i.d.) and direct large‐volume injections (1–10 μL) of aqueous samples have been studied. As an application, the verification of nonproduction of chemical warfare agents and their alleged use have been investigated by analyzing their hydrolysis products in spiked surface water and soil samples. The application of both the precolumn technique and large‐volume injections permit the detection of organophosphorus acids in water and soil at the low ppm level.
Verification of nonproduction of chemical warfare agents: II. Large volume injections in microcolumn liquid chromatography using flame photometric detection
Authors: Kientz Charles E. , Verweij Albert , De Jong Gerhardus J. , Th. Brinkman Udo A. 
Published: May 2005

AbstractThe sensitivity and separation performance of microcolumn liquid chromatography coupled with a flame photometric detector were considerably improved by the direct injection of large sample volumes (approximately 10 μL) and by peak compression. Extremely narrow peaks can be obtained by adding displacers such as hydrochloric acid (ion‐exchange mode) or n‐butanol (reversed‐phase mode) to the sample.The system was used for the determination of ethyl methylphosphonic acid, isopropyl methylphosphonic acid, and pinacolyl methylphosphonic acid which are the hydrolysis products of the super‐lethal nerve agents VX, sarin, and soman, respectively, and of the final degradation product, methylphosphonic acid. The detection limits for the alkyl methylphosphonic acids and sarin in water were 1–20 ppb.Two examples were used to demonstrate the practicality of the present procedure. Sarin and the much more polar isopropyl methylphosphonic acid were simultaneously determined in a spiked surface water sample used for verification studies. Low‐ppb levels of phosphorous acid were identified in mustard gas.
Purification of proteins and peptides for sequence analysis using microcolumn liquid chromatography
Authors: Moritz Robert L. , Simpson Richard J. 
Published: May 2005

AbstractReversed phase microcolumn (0.32 mm i.d.) liquid chromatography was used to purify low‐picomole amounts of proteins and peptides suitable for structural analysis. Using this approach, rapid trace enrichment (concentration) of low nanogram levels of proteins from volumes as high as 500 μL down to 1–2 μL was demonstrated. The total system recovery (including manual collection and reinjection) for 50 ng of lysozyme was >95%; the overall recovery after five injections was 90%. Using the same packing, Brownlee RP‐300, the resolution of a standard mixture of proteins was comparable for columns varying in length from 250 mm to 10mm. Identification by amino acid sequence analysis of selected peptides recovered from a sub‐10 pmol Staphylococcus aureus V8 protease digest of recombinant murine interleukin‐6 (IL‐6) was achieved.
Immobilized metal affinity chromatography with fused silica microcolumns
Authors: Flurer Cheryl L. , Novotny Milos 
Published: May 2005

AbstractFused silica capillaries of 250 μm i.d. were slurry‐packed with a TSK Chelate‐5PW stationary phase. Cu(II) was immobilized on the iminodiacetate surface, and proteins were separated using either an increasing imidazole gradient or a decreasing pH gradient. The microcolumn system increases detection sensitivity without affecting chromatographic behavior. The possible use of this system in the study of tertiary structure relationships between related proteins is explored.
Measurement of thermodynamic quantities of micellar solubilization by micellar electrokinetic chromatography with sodium dodecyl sulfate
Authors: Terabe Shigeru , Katsura Takehisa , Okada Yukihirao , Ishihama Yasushi , Otsuka Koji 
Published: May 2005

AbstractMicellar electrokinetic chromatography (MEKC) allows the calculation of distribution coefficients between a micelle and the surrounding aqueous phase from the measurement of the migration time, provided the critical micelle concentration (CMC) and the phase ratio are known. Thermodynamic quantities such as enthalpy and entropy changes of micellar solubilization were calculated from the temperature dependence of the distribution coefficients. Sodium dodecyl sulfate (SDS) was employed to prepare a micellar solution and its CMCs and partial specific volumes at different temperatures were measured. The relationship between the molecular structures of solutaes and the resulting thermodynamic quantities was investigated. The temperature inside the capillary was calculated from the temperature dependence of the distribution coefficient.
Diluted versus undiluted cyclodextrin derivates in capillary gas chromatography and the effect of linear carrier gas velocity, column temperature, and length on enantiomer separation
Authors: Hardt Ingo , König Wilfried A. 
Published: May 2005

AbstractThe effect of dilution of the chiral stationary phase octakis (3‐O‐butyryl‐2, 6‐di‐O‐pentyl)‐γ‐cyclodextrin in the achiral polysiloxane OV–1701 on the separation factor was investigated over a wide concentration range. The loss in enantioselectivity was only negligible down to a dilution of 50% (w/w), since the separation factor vs. concentration curves levels off at higher concentrations. Because of the strong temperature dependence of the separation factors, the properties of short columns (10 m and 4.5 m) were evaluated. These short columns, which allow operation at low temperatures and lead to enhanced separation factors were found to be appropriate for the separations of simple mixtures, because the gain in selectivity exceeded the loss in separation efficiency. For complex mixtures, the higher efficiencies of columns of at least 25 m in length were still necessary. A plot of In α vs. 1/T did not yield straight lines, but showed a significant curvature, leading to considerable relative errors if thermodynamic data were derived from these plots.
Simple method for the preparation of highly efficient polymer‐coated capillary electrophoresis columns
Authors: Malik Abdul , Zhao Zhongxi , Lee Milton L. 
Published: May 2005

AbstractA simple method for the preparation of polymer‐coated fused silica capillary columns for electrophoresis is presented. It is shown that the static coating technique used in GC and SFC can be conveniently utilized for the preparation of highly efficient capillary electrophoresis columns. In this method, the coating solution contains appropriate proportions of three ingredients: a polymer, a surface derivatization reagent, and a crosslinking reagent dissolved in a suitable low‐boiling solvent. After coating, the column is subjected to heat treatment to immobilize the polymer film. Simplicity, rapidity, high column efficiency, batch‐to‐batch and run‐to‐run reproducibility, and long column life‐time are advantageous features of the new method. Column efficiencies of as high as 1.2 million theoretical plates were achieved for cytochrome c on a 96 cm long Ucon 75 H‐90,000 coated column. Efficient electrophoretic separation of five cytochrome c proteins was achieved on a Superox 4 coated column. The possibility of CE separation of histones on the new columns was also explored.