bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhanced radial dispersion in open tubular column chromatography
Authors: Sumpter Sheldon R. , Lee Milton L. 
Published: May 2005

AbstractRadial diffusion of solutes in the mobile phase limits the practical linear velocities that can be used to increase speed of analysis in conventional open tubular column chromatography. Several methods have been devised to enhance radial dispersion that do not depend only on molecular radial diffusion. In this review, the methods of enhancing dispersion found in the chromatographic literature are discussed. These methods include the use of deformed columns, and spinning band and static mixer columns. These techniques have been found to be of little value in analytical chromatography. Electroosmotic flow has been used to generate a plug‐like flow profile in LC and generates one to two orders of magnitude lower plate height than produced at laminar flow conditions. Turbulent and secondary flow have been used to enhance radial diffusion in open tubular columns for gas, liquid, and supercritical fluid chromatography. These techniques are described from their theoretical and practical aspects.Turbulent flow has been investigated as a means for enhancing radial dispersion in open tubular column chromatography for several years. At low linear velocities (Reynolds numbers < 2000), the Golay equation accurately predicts that increasing velocities generate higher plate heights. However, turbulent flow experimental results have shown that unretained solutes have decreasing plate heights with increasing velocity after a critical velocity is achieved. Up to this time, turbulent flow chromatography has not been shown to be useful for retained solutes, and applications in analytical separations are absent in the literature.Secondary flow has also been studied by several investigators for the enhancement of radial dispersion. A circular, radial flow profile can be generated by centrifugal forces in tightly coiled columns, and after a critical velocity is achieved, columns coiled to appropriate aspect ratios yield lower plate heights than straight columns for unretained solutes as the velocity is increased. Although retained solutes yield higher plate heights in coiled rather than conventional straight columns in some cases due to the resistance to mass transfer at the interphase region, higher speeds of analysis are obtained. Secondary flow chromatography has been successfully applied in gas and supercritical fluid chromatography for the rapid separation of alkanes having low retention. Nevertheless, applications using secondary flow in chromatographic separations are limited.
Influence of temperature on the separation properties of immobilized Carbowax 20M open tubular column liquid chromatography
Authors: Janák Karel , Horká Marie , Krejčí Miloš 
Published: May 2005

AbstractProperties of Carbowax 20M stationary phase immobilized with pluriisocyanates were investigated in the temperature interval 20–80°C. Phase transition was observed under both GC and LC conditions. Depending on the type of crosslinking agent, different phase transition temperature intervals were found with the same end point transition temperature of 55°C in the GC system and 60°C in the LC system. In contrast to GC, the retention behavior of the columns in the LC system is not significantly influenced by phase transition. A severe drop of the height equivalent to a theoretical plate was observed near the phase transition in both systems. It was due to the increase in diffusivity of the stationary phase.
New silarylene/methylphenylsiloxane copolymer stationary phase for open tubular gas chromatography
Authors: Janák Karel , Hägglund Ingela , Blomberg Lars G. , Claude Saturnin G. , Tabacchi Raffaele 
Published: May 2005

AbstractA new silanol‐terminated silarylene/siloxane copolymer, having 30% phenyl and 1.5% vinyl substitution, has been evaluated for use as a stationary phase in gas chromatography. The polymer was found to be auto‐cross‐linkable. The highest degree of immobilization (90%) was obtained at relatively low temperatures (300°C). The auto‐cross‐linking at lower temperatures might be due to a silanol catalyzed reaction of vinyl groups. At higher temperatures (350–370°C) scission of phenyl groups and the formation of branched structures are the dominating immobilization reactions. Column polarity is thereby decreased.Thermal stability was excellent at 370°C after conditioning at this temperature. The utility of the columns was illustrated by the separation of polycyclic aromatic compounds.
Preservation of column efficiency when using solvent vent injection in open tubular column supercritical fluid chromatography
Authors: Koski Iina J. , Markides Karin E. , Lee Milton L. 
Published: May 2005

AbstractThe use of small internal diameter precolumns (11–25‐μm i. d.) helped solute focussing when using solvent vent sample introduction in open tubular column supercritical fluid chromatography (SFC). Column efficiencies were similar to those obtained with split injection (3000–5000 plates m−1). Trace analysis in SFC was improved because large volumes (1 μL) could be introduced for analysis with little sacrifice in column efficiency.
Liquid chromatography capillary columns dry‐packed with polar and nonpolar stationary phases
Authors: Crescentini Giancarlo , Mastrogiacomo Anna Rita 
Published: May 2005

AbstractFused silica capillary columns of 0.250‐mm i.d., packed with 5‐μm particles of nonpolar (octadecyl, octyl, and butyl) and polar (silica, diol, cyano, and amino) materials, have been prepared using a dry‐packing technique. The performance of the columns has been evaluated using the reduced plate height/reduced velocity equation and the separation impedance values. A comparison with similar slurry‐packed columns shows that the dry‐packing method may yield, in most cases, columns of analogous or better efficiency and requires a simpler apparatus and a shorter time for column preparation.
Chemical ionization mass spectrometry and gas chromatographic identification of some nitrogen‐containing volatile compounds from large‐scale pyrolysis of poly (acrylonitrile‐butadiene‐styrene) plastics
Authors: Shapi Michael M. , Riekkola Marja‐Liija 
Published: May 2005

AbstractA number of volatile pyrolyzates of large‐scale thermolysis of ABS and SAN plastics, which include phenyl substituted aliphatic nitriles and dinitriles, have been tentatively identified by GC‐MS. The exact isomers of most of these compounds have, however, not been specified, owing to limitations of 70 eV electron ionization (EI) mass spectrometry and temperature‐programmed retention indices in the absence of model compounds. In this study, some of the isomeric forms of these compounds were clarified using chemical ionization (CI) mass spectrometry and capillary gas chromatography (GC) involving model compounds. The presence of phenylacetonitrile, 2‐phenylpropanenirile, 3‐phenylpropanenitrile, trans‐3‐phenyl‐2‐propenenitrile, and 4‐phenylbutanenitrile among the pyrolyzates was confirmed by GC. Isobutane and methane CI of the nitriles yielded intense MH+ and adduct ions of low to medium intensity. Most of the smaller phenyl substituted nitriles tended to fragment by loss of 27 mass units, attributed to HCN. Isobutane CI of the larger molecules produced more fragmentation than methane CI which yielded little or no fragmentation. The reliability of the CI spectra was limited to the role of providing molecular formula information and some indirect evidence for the presence of the nitrile group in the molecules.
Supercritical fluid extraction of pesticides and phthalate esters following solid phase extraction from water
Authors: Ezzell John L. , Richter Bruce E. 
Published: May 2005

AbstractSolid phase extraction (SPE) was evaluated as a sample pretreatment method prior to supercritical fluid extraction (SFE) of pesticides or phthalate esters from spiked water samples. ODS, Florisil, Tenax GC and XAD4 resin were evaluated for their abilities to retain a mixture of 5 pesticides, and the use of supercritical CO2 as an elution solvent was investigated. SPE disks, impregnated with C8 bonded phase silica were examined in both off‐ and on‐line SFE. Using SPE disks prior to off‐line SFE, supercritical CO2, and modified CO2 yielded recoveries comparable to liquid solvent extraction for five pesticides and four phthalate esters at the 100 ppb level. On‐line SFE following disk SPE of chlorpyrifos at the 10 and 1 ppb levels yielded recoveries of 92 and 91%, respectively (%RSD = 7). The natures of supercritical solvents and their possible roles in the analysis of water samples is discussed.
Role of a microbore capillary column in the development of a portable gas chromatograph‐mass spectrometer
Authors: Sinha Mahadeva P. , Gutnikov George 
Published: May 2005

AbstractFor the development of a portable gas chromatograph‐mass spectrometer (GC‐MS) system, drastic reduction in the carrier gas load is necessary in order to minimize the pumping requirements of the mass spectrometer. Two approaches were investigated for achieving this. The first involved the use of a palladium‐hydrogen interface and was found not to be viable due to its chemical reactivity. The second utilized a short microbore capillary column (3−m × 50−μm i.d.). The small cross‐sectional area of the column reduced the gas load into the MS and yielded sharp chromatographic peaks possessing full‐widths at half‐height in the range of 200–600 ms from a mixture of priority pollutants. Good column efficiency (> 2.3 × 104 theoretical plates/meter for k of 10) and resolution were observed, and analyses were completed within a few minutes. Mass spectral measurements were performed with a miniaturized focal plane mass spectrograph having an integrating array detector. Because this system detects (integrates) ions of all masses simultaneously and continuously, short data acquisition times can be used to measure several spectra per gas chromatographic peak without loss in sensitivity. Such time‐resolved mass spectral measurements were applied to the separation and identification of benzene and carbon tetrachloride which coeluted from the column. Our results show that a short microbore capillary column in conjunction with a miniaturized mass spectrograph and an array detector is eminently suited for the development of a field portable GC‐MS system of high performance.
Isoelectric focusing of proteins in a microcapillary with universal concentration gradient detection
Authors: Wu Jiaqi , Pawliszyn Janusz 
Published: May 2005

AbstractProteins were separated by capillary isoelectric focusing (CIEF) performed in a 5‐μm i.d., 12‐cm long uncoated capillary, and detected by an on‐column concentration gradient detector based on Schlieren optics. The narrow capillary allows the application of a 15‐kV separation voltage. The high voltage resulted in a very narrow 30‐μm wide zone for carbonic anhydrase, which corresponded to a 60‐fL zone volume. All focused proteins could be detected by the universal concentration gradient detector without derivatization in less than 7 min. On‐column mass detection limits for proteins were at the 100 amol level, which was lower than that of a UV‐vis absorption spectrometric detector. The detection volume of the detector was calculated to be 20 fL, the smallest detection volumes reported to date for optical or spectroscopic detectors. This microcapillary CIEF‐concentration gradient detector system may be a useful technique for direct analysis of proteins at the single cell level.
Temperature and pressure controlled UV detector for capillary supercritical fluid chromatography
Authors: Hirata Yukio , Katoh Seiki 
Published: May 2005

AbstractA method of controlling UV cell pressure was developed for capillary supercritical fluid chromatography. The cell pressure was kept constant even during pressure programming. This allowed the use of the UV detector at high sensitivities without base‐line drift. It could also be used as a refractive index detector. The detection limit for chrysene at 269 nm was 10 pg at S/N = 2.
Effects of 1‐alkanols on separation performance in micellar electrokinetic capillary chromatography
Authors: Aiken Joseph H. , Huie Carmen W. 
Published: May 2005

AbstractThe effects of alcohols on separation performance in micellar electrokinetic chromatography were investigated using a test mixture containing a variety of substituted phenols. The addition of small amounts (0.5% v/v) of 1‐alkyl alcohols (1‐alkanols) into the electrophoretic buffer containing sodium dodecyl sulfate (SDS) was found to improve the resolution of certain solutes by extending the elution range and changing the selectivity, without causing significant variations in the electroosmotic velocity or column efficiency. The enhancement in resolution was found to be a function of the carbon chain length (C4C8) as well as the mole ratio of the 1‐alkanols.
Solute retention and selectivity behavior in linear‐temperature‐programmed, constant‐density supercritical fluid chromatography
Authors: Chester Thomas L. , Innis David P. 
Published: May 2005

AbstractWhen temperature programming is performed in supercritical fluid chromatography (SFC) under conditions where the solute‐mobile phase interactions are approximately fixed, that is, with the use of constant mobile phase density, then positive temperature programs can be used. The results resemble those in temperature‐programmed gas chromatography (GC) except that chromatograms are compressed and solutes elute at lower temperatures. For a given temperature‐program rat, the extent of this compression effect is controlled by the (fixed) mobile phase density. When a methylsilicone stationary phase is used along with CO2 mobile phase, the compression occurs with little change in selectivity. However, with a biphenyl‐substituted polysiloxane stationary phase, selectivity shifts occur for some solutes (vs. hydrocarbons) as the density is varied. The effect is even greater and affects more solutes when a cyanopropyl‐substituted polysiloxane stationary phase is used.This selectivity behavior differs from the temperature‐dependent selectivity behavior known in GC. In GC only the forces between solutes and the stationary phase are involved. But in SFC, mobile phase interactions with both the solutes and the stationary phase are also important. The large selectivity shifts we observe in SFC most likely arise because of stationary phase swelling by the mobile phase. This is a function of the temperature and mobile phase density (or pressure) and can be tuned without changing the composition of the mobile phase. It is possible to use either temperature or density to adjust or fine‐tune selectivity between a pair of solutes while using the other parameter to adjust retention of the pair.These experiments further suggest that GC is not only a special case of SFC (where the solute‐mobile phase interactions are essentially zero), but that SFC possesses an additional and extremely powerful selectivity adjustment mechanism not available in GC.
Independently temperature programmed uncoated precolumn: A concept for improved sample introduction in capillary GC
Authors: Hagman Gunnar , Roeraade Johan 
Published: May 2005

AbstractIn this paper, a GC sample introduction technique is described in which an uncoated precolumn and the analytical capillary column are individually temperature programmed. The influence of different rates of temperature programming of the retention gap on band broadening of a series of n‐alkanes has been investigated for different lengths of the precolumn. It is shown that extra column band broadening of high boiling solutes is reduced when the temperature of the precolumn is ramped at a faster rate than the analytical column. This benefit is particularly pronounced when long retention gaps are employed.The technique extends the useful lifetime of the analytical column when complex real‐world samples with a wide volatility range are analyzed. This is due to the fact that the final temperature of the precolumn can be kept below the final temperature of the analytical column. Thus, the column is not contaminated with high boiling non‐elutable solutes.
Ampholyte‐free isoelectric focusing of proteins in cone shaped capillaries
Authors: Pawliszyn Janusz , Wu Jiaqi 
Published: May 2005

AbstractA simple method of generating pH gradients for use in capillary isoelectric focusing was described and evaluated experimentally. In the proposed scheme, the cone shaped capillary filled with a conventional buffer is used to produce an effect of nonuniform heating which then generate temperature and corresponding pH gradients along the capillary axis. Concentration and separation of proteins by applying a simple isoelectric focusing system based on this principle is demonstrated. An inexpensive absorption imaging detection system is used to continuously monitor progress of the separation and concentration processes.
Effect of column diameter on plate height in high speed liquid chromatography using pellicular and perfused particles in packed capillaries
Authors: Cole Laura J. , Schultz Nicole M. , Kennedy Robert T. 
Published: May 2005

AbstractThe purpose of this work was to examine column designs that allow for rapid separations by packed capillary liquid chromatography. Previous work with packed capillary columns with inner diameters (i.d.'s) of 20 to 150 μm revealed significantly reduced eddy diffusion broadening in these columns compared to larger bore columns. These results suggested that resistance to mass transfer dominates band broadening in microcolumns at high flow rates. Thus, it should be possible to attain rapid separations in capillaries by using pellicular or perfused particles which reduce resistance to mass transfer in the stagnant mobile phase. Furthermore, the use of capillary columns with small eddy diffusion effects should give better performance than larger bore columns packed with similar particles. To test these possibilities, the plate height of an unretained solute as a function of flow velocity was evaluated in columns with internal diameters of 50 to 250 μm packed with pellicular particles (8 and 15 μm diameter) and perfusion particles (10 and 20 μm diameter). Decreasing both column i.d. and column i.d. to particle diameter ratio (ρ) were found to improve the performance of columns packed with pellicular particles; however, ρ was the most important factor. Column i.d. and ρ had no effect on the performance of perfusion particles within the range tested. However, the capillary perfusion columns had better performance than previously reported for larger bore perfusion columns. The best results were obtained for 8 μm pellicular particles inside 50 μm i.d. columns. These columns generated nearly 7,000 theoretical plates in 10 s. Further improvements should be possible by using smaller particles and smaller column internal diameters.
Investigation of retention and selectivity in high‐temperature, high‐pressure, open‐tubular supercritical fluid chromatography with CO2 mobile phase
Authors: Chester Thomas L. , Innis David P. 
Published: May 2005

AbstractWe studied solute retention for n‐hydrocarbons, (low‐molecular‐weight) polystyrenes, an ethoxylated surfactant, and a selectivity test mix on open‐tubular columns with methyl‐, biphenyl‐, and cyanopropyl‐substituted stationary phases for pressures up to 680 atm and temperatures up to 240°C. The solute elution range varied tremendously with column choice, with the least retentive stationary phases providing the highest elution range. However, the best resolution and largest analysis range were obtained with the most retentive stationary phase and the highest pressures. Increasing the temperatures above 160°C did not cause a large increase in elution pressure for the solutes used in this study. Exceptionally large shifts in selectivity with temperatures up to about 160°C occurred for the biphenyl and cyanopropyl stationary phases. The availability of pressures higher than 680 atm, coupled with adequately retentive stationary phases used at optimal temperatures, would further increase the analysis scope of opentubular supercritical fluid chromatography.
Pharmaceutical applications of a bonded cyclodextrin stationary phase
Authors: Juvancz Zoltan , Grolimund Karl , Schurig Volker 
Published: May 2005

AbstractOpen tubular columns were coated with Chirasil‐Dex, a polysiloxane anchored permethylated β‐cyclodextrin stationary phase. A number of chiral separations of pharmaceuticals and agrichemical are presented to demonstrate the usefulness of this stationary phase in both GC and SFC. Racemates of various amines, amino acids, amino alcohols, carboxylic acids, coumarines, diols, and imides were resolved. To achieve acceptable separation of some enantiomers, a series of derivatives were studied. In many cases, cyclic derivatives and free acids gave the highest enantioselectivity.
Reproducibility of the determination of caffeine in coffee by micellar electrokinetic capillary chromatography
Authors: Burton D. Edward , Powell Larry L. , Xi Xiaobing 
Published: May 2005

AbstractSamples of regular and decaffeinated varieties of green coffee beans, instant coffee, and “roast & grind” coffee have been examined by micellar electrokinetic capillary chromatography (MECC). The separation conditions affecting the reproducibility of the determination of caffeine in these samples are presented. Sodium dodecyl sulfate (SDS) and cetyltrimethylammonium chloride (CTAC) Were employed to demonstrate the role of the surfactant system in reproducibility. The use of NaOH and HCl was explored for column rinsing to enhance the stability of the electroosmotic flow. The levels of caffeine ranged from 3.95% (by weight) for regular coffee to 0.07% for decaffeinated coffee. The relative standard deviation (RSD) for the migration time of the peak corresponding to caffeine in coffee samples was 0.74%. The RSDs for the peak areas and heights were 1.04 and 2.07%, respectively. The results of the quantitation of caffeine by MECC are compared to levels determined by high‐performance liquid chromatography (HPLC).
Supercritical fluid extraction and capillary gas chromatography of the rhizomes of Z. zerumbet
Authors: Ahmad Umi K. , Sirat Hasnah M. , Sanagi M. Marsin , Smith Roger M. 
Published: May 2005

AbstractSupercritical carbon dioxide at 60°C and 200 bar has been used to extract the nonpolar components of the dried rhizomes of Zingiber zerumbet. The extract could be fractionated by placing an on‐line silica column before the pressure relief valve. The extracts were analyzed using capillary GC and GC‐MS. This technique provides an effective means of sample preparation and a relatively fast way of determining the constituents of plant materials.
On‐column ITP focusing in CZE for the quantitation of low‐molecular‐weight basic solutes in biological samples
Authors: Larsson Marita , Någård Sofia 
Published: May 2005

AbstractCapillary zone electrophoretic (CZE) separations were performed after the injection of large sample volumes by use of a discontinuous buffer system for analyte focusing. Up to 700 nL were injected into a 75 μm i.d. capillary, corresponding to a 23 cm long sample zone. Automated analyses were performed in a commercially available instrument, which was modified to work with a larger pressure drop for hydrodynamic injection. The method was adapted to the determination of a low‐molecular‐weight enzyme inhibitor, DuP 714, in aqueous samples and a structurally related test compound in extracts from plasma samples. The separation system based on a coated capillary was stable and reproducible over several weeks use for aqueous samples, but the analysis of large volumes (> 600 nL) of solid‐phase extracts from plasma, containing acetonitrile, indicated that there is a need for more stable coatings or more extensive sample cleanup. Calibration curves are presented for the test substances, showing a linear relationship between the area ratio of the solute vs. an internal standard and the concentration. Samples containing 50–100 nmol L−1 of solute could be successfully analyzed by CZE with UV detection at 215 nm, approaching levels that are relevant for bioanalytical applications.