bluuebunny/crossref_metadata_2025_split huggingface dataset:
Refractometric detector for a microcolumn high‐performance size‐exclusion and micro gel chromatograph
Authors: Alexandrov Maxim L. , Belenkii Boris G. , Gotlib Vladimir A. , Kever Jeno E. 
Published: May 2005

AbstractIt is shown that an interference‐polarizing refractometric detector makes it possible to use microcolumn size‐exclusion chromatography (MSEC) columns with inner diameters of 0.2 to 0.5 mm and ensures a detection limit (at a signal to noise ratio of 3) of 8 × 10−8 refractive index units.Taking into account the above requirements, a micro‐gel chromatograph with a refractometric (interference‐polarizing) detector was developed. Teflon columns gave reproducibilities (the mean square deviation at the 95% confidence level) of retention times and signal amplitudes of 0.2% and 0.5%, respectively, which ensures reproducibilities of molecular weight determinations within about 2 to 4%. Examples of polymer and protein analyses carried out on this chromatograph are given. It is suggested that a micro‐gel chromatograph can be developed for fused‐silica capillary columns with inner diameters of 0.2 mm. This would permit analysis of approximately 10 pg of polymer.
Capillary GC analysis of biogenic amines, their precursors and catabolytes after fast derivatization with ethyl chloroformate
Authors: Hušek Petr 
Published: May 2005

AbstractSix aromatic biogenic amines, three aromatic amino acid precursors, four aromatic hydroxycarboxylic acid catabolytes, and two aromatic glycols were analyzed by capillary GC after derivatization. Instantaneous derivatization was performed by reaction with ethyl chloroformate in a medium of aqueous acetonitrile containing ethanol and pyridine. After extraction of the derivatives into chloroform, the sample was ready for analysis.
Separation of C60 and C70 fullerenes on methoxyphenylpropyl bonded stationary phases in microcolumn liquid chromatography
Authors: Jinno Kiyokatsu , Saito Yoshihiro , Chen Yung‐Lin , Luehr Gary , Archer Jim , Fetzer John C. , Biggs Wilton R. 
Published: May 2005

AbstractChromatographic separation of C60 and C70 fullerenes was performed with phenylpropyl and three different methoxyphenylpropyl bonded phases in microcolumn liquid chromatography. The results indicate that the 3,4‐dimethoxyphenylpropyl phase possesses the best resolving power among the evaluated phases, producing a separation factor of 1.87 for C70 and C60 using n‐hexane as the mobile phase. This observation could be explained by examining the energy minimized conformations of the bonded phases and their associative interactions with the fullerene molecules.
Direct chiral resolution of amino acid derivatives by capillary electrophoresis
Authors: Okafo George N. , Camilleri Patrick 
Published: May 2005

AbstractA mixture of sodium deoxycholate and β‐cyclodextrin has been used to resolve the enantiomers of the 1‐cyano‐2‐substituted‐benz[L]isoindole and dansyl derivatives of a variety of amino acids. The enantiomers of CBI‐histidine and glutamic acid were resolved with this system unlike the case of γ‐cyclodextrin in combination with SDS reported in the literature. Dansyl derivatives have been generated in situ to provide information about the migration behavior of dansylic acid, a major by‐product in the dansylation.
Fullerene‐linked particles as LC chromatographic media and modification of their electron donor/acceptor properties by secondary chemical reactions
Authors: Stalling David L. , Guo Congyuan , Kuo Kenneth C. , Saim Said 
Published: May 2005

AbstractFullerenes (C60 and C70) linked to small silica or polymer particles provide novel chromatographic stationary phases with electron donor/acceptor surface interactions that may parallel those of aromatic carbons. Separations of fullerenes and aromatic compounds frequently encountered as environmental contaminants were investigated using LC microcolumns containing either particles prepared from BrHC60 linked to amino‐silica (Spherisorb‐NH2, Phenomenex) or porous polymers containing ca. 12% fullerene by weight. The polystyrene divinylbenzene (PSDVB)‐C60/70H column had greater capacity (k') than the SiNHC60/70H column. Toluene and polycyclic aromatic hydrocarbons (PAHs), naphthalene, anthracene, pyrene, and perylene, were retained in the order of increasing ring number; nitro‐substituents increased retention; and chlorinated‐dibenzo‐p‐dioxins and ‐dibenzofurans were more strongly retained than their parent compounds. PCB congeners with no chlorine in the ortho, ortho'‐positions are co‐planar and are strongly retained; for these isomers, retention increased with higher chlorination. We demonstrate that surface‐linked fullerenes can also accommodate further chemical modification through the addition of 2‐(4‐nitrophenyl)ethyl or ‐NHCH2CH2NH2 moieties to yield altered electron donor/acceptor affinity. Separations appear to be derived primarily from aromatic electron induced dipole‐dipole or electron‐pair donor or acceptor interactions (charge transfer complexes). Except for the fullerenes, surface interactions with compounds are largely suppressed with methylene chloride as the mobile phase.
Band broadening during mobile phase change in unified chromatography (GC‐SFC)
Authors: Tong Daixin , Bartle Keith D. 
Published: May 2005

AbstractBand broadening brought about by changing the mobile phase from the GC mode to the SFC mode in unified chromatography is discussed. Its origin is shown to result from several factors: the replaceable volume of the tubing and valves in front of and following the column; the volume, internal diameter, and film thickness of the open tubular column; the initial pressure of the supercritical mobile phase; and the column temperature. Improvements to restrict band broadening were achieved by optimizing the system and its operating conditions.
Polymeric hollow fibers for capillary electrophoresis
Authors: Liu Peter Z. , Malik Abdul , Kuchar Marvin C. J. , Vorkink William P. , Lee Milton L. 
Published: May 2005

AbstractIn this paper, polymeric hollow fibers prepared from polypropylene and polybutylene terephthalate were used as CE columns. Surface modifications with polyacrylamide greatly improved the performance of the capillaries. Separations of substituted pyridines, model proteins and standard ribonucleotides were demonstrated. The column efficiency for model proteins was over 200,000 theoretical plates. Comparisons of electroosmotic flow, UV absorption properties, heat dissipation, and diameter variation between fused silica capillaries and polymeric hollow fibers were made. The practical potential of small diameter polymeric hollow fibers as CE columns was evaluated.
Preparation and evaluation of an on‐line preconcentrator for capillary electrophoresis
Authors: Hoyt Arthur M. , Beale Stephen C. , Larmann John P. , Jorgenson James W. 
Published: May 2005

AbstractThe preparation and performance of an on‐line preconcentrator for capillary electrophoresis (CE) is described. Borosilicate glass microspheres were dry‐packed into the fused silica column terminus and sintered in place with a micro electric are developed for this application. Reversed‐phase LC packing material was slurry‐packed onto this frit, in lengths of 1‐3 mm. An additional frit of borosilicate beads behind the preconcentrator was used to fix the packed bed in place. The performance of the packed bed preconcentrator for the enhancement of UV and fluorescence detection limits was evaluated. Construction of the micro electric are device, the packing procedures, and practical applications are described.
Preparation of long packed capillary columns using carbon dioxide slurries
Authors: Malik Abdul , Li Wenbao , Lee Milton L. 
Published: May 2005

AbstractA new, reproducible method is described for the preparation of highly efficient fused silica packed capillary columns using pressure programmed liquid or supercritical carbon dioxide to carry the packing material into the capillary. The method allows facile preparation of long, uniformly packed capillary columns capable of producing over 240,000 theoretical plates in SFC. Columns of up to 10 meters in length were prepared using LC packing materials of different chemical nature and particle size. The new method does not require a separate step for preparing the slurry, and it is free from the drawbacks inherent in conventional slurry‐packing methods. The lower viscosity and surface tension of carbon dioxide compared to conventional slurry‐forming liquids, as well as the use of ultrasonic vibration and pressure programming in the packing process, provide favorable conditions for achieving packing uniformity over greater column lengths than is achievable by other packing techniques. Proper restrictors and appropriate decompression rates during the use of these columns in SFC were found to be very important in achieving optimum column performance. In comparison to the use of open tubular columns, higher effciencies, greater sample capacities, and faster analysis speeds can be obtained. These advantageous features make the newly developed columns suitable for trace analysis, separation of very complex mixtures, and analysis of difficult‐to‐separate solutes.
Correlation of resolution with frictional coefficients and pKavalues in capillary electrophoresis of four diuretics: Determination of electric field strength and electroosmotic velocity
Authors: Jumppanen Juho H. , Sirén Heli , Riekkola Marja‐Liisa , Söderman Olle 
Published: May 2005

AbstractUnder ideal conditions in capillary zone electrophoresis, the frictional coefficients (f) and pKavalues of the analytes can be used to predict their separation under various conditions. These parameters can also be used to determine whether or not the separation depends solely on electrophoretic mobilities. Moreover, marker compounds with known electrophoretic mobilities can be used in ideal systems to yield information on pKavalues or on frictional coefficients for molecules at infinite dilution that cannot be studied by more widely used techniques. Fourier transform pulse gradient spin‐echo nuclear magnetic resonance spectroscopy is a standard method for measuring diffusion coefficients, from which the frictional coefficients were obtained. The good correlation between measured values of f and the observed elution times of four diuretics at pH 10.6 (20°C, CAPS 0.06 M) proved that the separation was based on the electrophoretic mobilities only. To be able to study the system accurately, the field strength and electroosmotic flow were measured empirically by using acetazolamide and clopamide as markers. The electric field strength in the electrolyte was found to be approximately 20% lower than expected. Simple equations are presented, which allow the measurement of these two quantities with the help of two compounds of known electrophoretic mobilities. To yield reliable results, the compounds should have electrophoretic mobilities differing by a factor of 2 or more.
Micro‐FFF: Theoretical and practical aspects of reducing the dimensions of field‐flow fractionation channels
Authors: Giddings J. Calvin 
Published: May 2005

AbstractThe value of miniaturizing field‐flow fractionation (FFF) channels is examined based on theoretical and experimental evidence. While FFF and chromatography are dynamically similar, the dimension analogous to capillary or particle diameter in chromatography is the Brownian excursion distance (ℓ), a "soft" dimension controlled by field strength and thus subject to significant reduction by increasing the field strength. Optimization of the “hard” channel dimensions (length, breadth, thickness) is a more complex matter involving diverse factors including sample dilution and detectability, clog‐free operation, edge effects, relaxation time, compatibility with pump and detector systems, and only in some cases the influence of these dimensions on the achievable ℓ.
Buckminsterfullerene as a stationary phase in liquid chromatography
Authors: Jinno Kiyokatsu , Fukuoka Katsunori , Fetzer John C. , Biggs Wilton R. 
Published: May 2005

AbstractBuckminsterfullerene C60 was used as a stationary phase for the microcolumn liquid chromatographic separation (LC) of various aromatic compounds. Carbonaceous material prepared by a general soot production process was extracted with toluene, purified using several chromatographic processes, and then packed into fused silica capillary columns for chromatographic evaluation. The performance and separation characteristics were examined. The results indicate that the C60 fullerene can be useful as an LC stationary phase and offers a unique shape selectivity for aromatic compounds as compared to conventional octadecylsilica phases.
Application of capillary electrophoresis to the quality control of pharmaceutical formulations: Effect of area correction on quantitation of antitussives
Authors: Korman Milos , Vindevogel Johan , Sandra Pat 
Published: May 2005

AbstractThe application of capillary electrophoresis for assaying the drug content of pharmaceutical formulations has been studied. Correction of area for migration times has been found useful in those cases where environmental conditions lead to increased migration time variability. From the results, the feasibility of single‐point calibration with an external standard was shown and experimentally verified.
Mixture of ammonia and helium as a carrier gas for capillary gas chromatography
Authors: Abdel‐Rehim Mohamed , Zhang Lin , Hassan Moustapha , Ehrsson Hans 
Published: May 2005

AbstractA mixture of ammonia and helium was used as a carrier gas for capillary gas chromatographic analysis of aliphatic amines and dichlorophenols. The peak symmetry for aliphatic amines was drastically improved when the percentage of ammonia was 5–30%. The symmetry continued to improve, although less drastically, between 30–100%ammonia. The capacity factors of the amines decreased with increasing ammonia content up to 100%. 2,5‐Dichlorophenol and 2,6‐dichlorophenol could not be resolved when helium alone was used as the mobile phase with a column of intermediate polarity (cyanopropylmethylphenylsilicone). Complete separation was, however, achieved by increasing the ammonia content in the carrier gas to 50%. The ratio of the capacity factors (k'NH3/k'He) for the dichlorophenols increased linearly with increasing ammonia percentage up to 100% on the methylsilicone and cyanopropylmethylphenylsilicone columns.
Shape selectivity assessment of stationary phases in gas chromatography
Authors: Sander Lane C. , Schneider Manfred , Wise Stephen A. 
Published: May 2005

AbstractColumn selectivity is examined for a series of smectic liquid crystalline columns and is compared with methyl and C18 polysiloxane columns for the separation of polycyclic aromatic hydrocarbon (PAH) isomers. A set of extended and condensed solute probes is described that provides a sensitive indication of variations in column shape selectivity. Examples of shape selectivity differences are presented for smectic liquid crystalline columns and 5% phenyl polysiloxane columns using various PAH isomer sets. Variations in selectivity have been observed among different smectic liquid crystalline columns, and this problem appears more significant than for methyl polysiloxane columns. The selectivity ration for tetraphenylmethane and p‐terphenyl provides a sensitive indication of column shape selectivity, with a change in elution order occurring between ordered (smectic liquid crystalline) columns and non‐ordered (methyl polysiloxane) columns. Shape selectivity differences indicated by this test mixture are apparent for more complex PAH isomer mixtures. Despite stationary phase selectivity variability, smectic liquid crystalline columns offer considerable potential for solving difficult separation problems involving structured solutes.
Performance of silica‐bonded quinolinol as a selective stationary phase for packed capillary supercritical fluid chromatography
Authors: Hägglund Ingela , Demirbüker Mustafa , Blomberg Lars G. 
Published: May 2005

AbstractSelective stationary phases are of crucial importance in packed column supercritical fluid chromatography (SFC), and a potentially powerful selective stationary phase, silica‐bonded 8‐quinolinol, has been evaluated. Its performance was compared with that of an aminopropyl modified silica. The 8‐quinolinol columns could be used at temperatures up to 150°C, while the aminopropyl columns were degraded above 90°C. The general performance of the quinolinol column was very good when utilizing a mobile phase containing a polar modifier. Reduced plate heights of 4.8 to 3.8 and symmetrical peaks were obtained. Further, the quinolinol phase showed excellent selectivities under supercritical conditions. This was demonstrated by the separation of fatty acid methylesters and azaarenes. In addition, changes in selectivity could readily be made by loading with metal ions.
Capillary gel electrophoresis
Authors: Dolník Vladislav 
Published: May 2005

AbstractCapillary gel electrophoresis (CGE) is a new rapidly developing method for biopolymer separations. It has been used successfully for separations of oligonucleotides, oligosaccharides, polyamino acids, and even for SDS electrophoresis of polypeptides. Shrinkage of the gel during polymerization, with resulting void formation as the main technological problem when making capillary gels, was overcome by several procedures. More recently, a modification of gel electrophoresis, using replaceable linear polymer solutions has gained popularity, especially for SDS electrophoresis of proteins and electrophoresis of DNA.
Capillary supercritical fluid chromatography with nitro‐ and nitroso‐specific chemiluminescence detection
Authors: Francis Eric S. , Eatough Delbert J. , Lee Milton L. 
Published: May 2005

AbstractThe thermal energy analyzer (TEA), a gas‐phase chemiluminescence detector which is specific for nitro and nitroso compounds, was evaluated as a detector for use with capillary supercritical fluid chromatography. The potential use of the TEA for thermally labile compounds and environmental samples was demonstrated. The TEA showed good sensitivity and broad linear dynamic range; minimum detectable quantities (MDQ) were below 20 pg for pentaerythritol tetranitrate (PETN) with a dynamic range of over 4 orders of magnitude. The analysis of cyclotetramethylene tetranitramine (HMX) was accomplished by using modified (CO2) with a corresponding MDQ of 67 pg. The selectivity of the TEA for nitro and nitroso compounds can be adjusted by changing the pyrolysis temperature. The SFC/TEA system was applied to a variety of nitro and nitroso compounds, and evaluated more extensively for routine analysis of propellant and explosive residues.
Solvent‐free sample introduction for supercritical fluid chromatography using polymer coated fibers
Authors: Hirata Yukio , Pawliszyn Janusz 
Published: May 2005

AbstractA solvent‐free sample introduction method for supercritical fluid chromatography that uses polymer coated fused silica fibers results in very stable baseline and high efficiency separations. The method has two steps: first, a fiber is exposed to a prepared mixture of target analytes or a sample so that the polymeric coating absorbs analytes, and second, the fiber is placed inside a piece of tubing connected to the column of a supercritical fluid chromatograph. The supercritical fluid carrier extracts analytes from the coating and transfers them onto the head of the column. Pressure programmed separation follows. The method was tested on high molecular weight and polar analytes using 100 and 50 μm i.d. capillary columns. Fibers with a polydimethylsiloxane coating were used to extract hydrophobic analytes, and fibers with a polyacrylate coating were used to extract more polar compounds.
Functional group selectivity using fluoroform as a mobile phase for supercritical fluid chromatography
Authors: Blackwell John A. , Schallinger Luke E. 
Published: May 2005

AbstractThe eluotropic strenght and chromatographic selectivity of fluoroform is compared to that of carbon dioxide and methanol‐modified carbon dioxide. Naphthalene derivatives were used as probe solutes in capillary supercritical fluid chromatography to determine the effects of fluid type, pressure, and temperature on selectivity and retention. Fluoroform is much stronger in eluotropic strengh than carbon dioxide or methanol‐modified carbon dioxide at the same temperature and pressure. Under the same reduced conditions, fluoroform is lower in eluotropic strength than carbon dioxide. Specific interactions between hydrogen bond accepting functional groups and fluoroform are observed. Functional groups capable of accepting hydrogen bonds contribute less of an increase in retention when using fluoroform while those capable of dispersive interactions contribute less of an increase in retention when using carbon dioxide.
Rapid separation of DNA restriction digests using size selective capillary electrophoresis with application to DNA fingerprinting
Authors: Clark Brian K. , Nickles Christine L. , Morton Ken C. , Kovac Jeffrey , Sepaniak Michael J. 
Published: May 2005

AbstractCapillary electrophoresis (CE) using running buffers containing a water soluble polymer (methylcellulose, MC) was employed for the rapid size‐selective separation and identification of plasmid DNA (pBR322 and pBR328). The two plasmid samples were distinguished based on differences in CE elution patterns resulting from injections of their Hinfl enzyme digests. The restriction fragments in the digests were detected by incorporating the DNA intercalation dye, ethidium bromide (EB), in the running buffer and utilizing laser fluorimetry. Short separation times were achieved by increasing the applied field, but with a concomitant decrease in fragment resolution. This behavior was attributed to three main effects: (i) a reduction in efficiency due to problems with Joule heating, (ii) a decrease in selectivity as the fragments elongate and align with the high fields, and (iii) a general reduction in system retention due to the fragment elongation and increased capillary temperature. The deleterious effects of Joule heating were minimized by employing small diameter capillaries and low buffer concentrations. The molecular weight of the MC polymer primarily influenced separation efficiency. Conversely, MC concentration influenced both selectivity and system retention. High efficiency (106 plates m−1) and good resolution of the fragments in the different restriction digests were achieved using running buffers containing 100,000 MW methyl cellulose at high fields. Under optimized conditions, the test plasmid sample digest provided reproducible and unique elution profiles with 120 s separation times.
Fused silica packed capillary columns in supercritical fluid chromatography
Authors: Li Wenbao , Malik Abdul , Lee Milton L. 
Published: May 2005

AbstractPacked capillary columns provide advantages of low flow rates, moderate sample capacities and loadabilities, short analysis times, high detectabilities, and the possibility of using a wide variety of commercially available stationary phases. This type of column is finding increasingly more applications in a variety of fields. In this paper, we report detailed studies using relatively long (0.5 to 10 m) packed capillary columns in SFC. Characteristics such as packing density and column stability are reported, as well as efficiency, resolution, and pressure drop for the different columns. It was found that densely packed capillary columns prepared using supercritical CO2 as the slurry fluid are more stable and generally have better performance than conventional solvent slurry packed columns.