bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimization via liquid phase mixtures in capillary gas chromatography
Authors: Takeoka G. , Richard H. M. , Mehran Mehrzad , Jennings W. 
Published: May 2005

AbstractThe use of sequentially coupled columns to achieve a binary liquid phase mixture has been simplified by the availability of zero dead volume fittings compatible with fused silica columns. The extent to which the velocity gradient through the coupled column affects the “apparent” liquid phase ratio can be determined by graphic interpolation; the length ratio of the coupled column segments can then be adjusted so that the “apparent” liquid phase ratio actually experienced by the solutes agrees with the targeted value. The fact that the direction of flow through the coupled column affects the chromatographic dispersion suggests that accepted generalizations on flow optimization throughout the column may not be precisely correct.
An attempt to extend ordinary capillary gas chromatography to supercritical fluid chromatography (SFC)
Authors: Grob K. 
Published: May 2005

AbstractSince capillary columns with well immobilized stationary phases are expected to withstand contact with supercritical fluids, we wished to study their amenability to SFC. Simultaneously, we wished to learn how far SFC can be accomplished with the ordianary tools of capillary GC.The study demonstrates that truly supercritical, not just relatively high, pressure is required to ensure the typical effects of SFC. Results obtained with sub‐and supercritical pressure are compared and discussed. A comprehenshive study of the parameters permitting SFC with capillary GC equipment showed a clear preference for CO2 as a carrier, FID detection, and oncolumn sampling. While no additional equipment is required, a critical feature is the flow restrictor to be mounted on the end of the column. The production and properties of this restrictor are discussed in detail. It is reasonable to hope that SFC with 0.1 mm id capillary columns can be realized in the pressure range of 100–150 bar, where substances which cannot be eluted from a capillary colum under GC donditions are expected to be analyzed.
Cold trapping of volatile organic compounds on fused silica capillary columns
Authors: Pankow J. F. 
Published: May 2005

AbstractA 30 m, 0.25 mm ID, fused silica capillary column at temperatures from –60 to –100°C has been shown to be a quantitative trap for organic compounds with volatilities ranging from that of 1, 1 ‐dichloroethene that of chlorobenzene. This type of “whole column cryotrapping” provided sharp peaks (peak width approximately 4–7 seconds) for all compounds at a trapping temperature of –80°C and with high carrier gas pressures and linear velocities (30 psi and 110 cm/s, respectively). Whole column cryotrapping possesses great simplicity, chromatographic efficiency (no trapping loop connections), and a built‐in indicator of quality assurance for trapping efficiency (i.e., peak shape). These advantages are extremely attractive and are indicative of the fact that the potential of this approach has not yet been fully appreciated.
Gradient separations of complex mixtures by micro high‐performance liquid chromatography
Authors: Takeuchi T. , Ishii D. 
Published: May 2005

AbstractHigh‐performance micro packed fused‐silica and open‐tubular glass capillary columns were prepared and applied to separations of complex mixtures. Solvent‐gradient elution proved quite useful for the separation of solutes with wide polarity. Instruments and some applications are described.
Flexible soft glass capillary columns vs. flexible fused silica capillary columns for gas chromatography‐a critique
Authors: Lipsky S. R. 
Published: May 2005

AbstractThe gas chromatographic use of flexible thin walled soft glass capillary columns coated with non‐polar stationary phases is compared to similar columns made of fused silica glass. With non‐polar soft glass columns, the use of surface roughening viagaseous HCI followed by a Carbowax 20 M pretreatment gave adsorptive phenomena, and thermal instability. With very polar soft glass columns where a variety of cyanopropyl silicone phases were coated directly onto the NaCI crystal matrix, adsorptive effects were again prominent and frequent break‐down in film stability with time, was also observed. These undesirable effects were due to the presence of metal oxides in the soft glass. Attempts to remove these materials from the thin walled soft glass surface by means of acid leaching produced significant brittleness. This deleterious result was further increased by attempts at high temperature silylation or polysiloxane deactivation.In sharp contrast, the fused silica surface was essentially free of metal oxides and the surface silanol groups are easily neutralized by silylation or polysiloxane deactivation techniques. No brittleness was observed following these procedures. An increasing series of high molecular weight, viscous, polymeric vinyl containing non‐polar and highly polar stationary phases have been produced which readily wet the surface of the fused silica and are easily crosslinked in the presence of free radical generators. These columns are essentially free of all the problems noted with flexible thin walled soft glass. When all of the parameters involved in the fabrication of a glass capillary column are assessed, it appears at this time, that the flexible fused silica glass column with cross linked phases approaches the “ideal” capillary column.
Solute focusing technique for on‐column injection in capillary gas chromatography
Authors: Hinshaw J. V. , Yang F. J. 
Published: May 2005

AbstractA novel solute focusing technique for on‐column injection of liquid samples onto capillary GC columns is described. The focusing technique allows injection of 8.0 microliters or more of sample without producing the peak distortion or splitting observed under conventional on‐column injection conditions. The experimentally determined performance of the technique is given for a wide volatility range sample. Solute focusing is useful in situations where on‐column injection of 1.0 microliter or greater is required.
Prediction of gas chromatographic retention indices of linear, branched, and cyclic alkanes from their physicochemical properties
Authors: Bermejo J. , Guillén M. D. 
Published: May 2005

AbstractKováts retention indices for a series of linear, branched, and cyclic alkanes on squalane at any temperature, and on other stationary phases of different polarity at a given temperature, are related to physicochemical properties of the solutes, such as boiling point and molar refraction, by multiple regression analysis. The equations found permit calculation of the Kováts retention index for all alkanes, with standard deviations close to experimental error. The same equations can also be used for calculating the physicochemical parameters they contain.
Peak broadening in isothermal runs due to large retention gaps in capillary GC?
Authors: Grob K. 
Published: May 2005

AbstractA simple formula is derived which allows estimation of the band broadening due to longitudinal diffusion in retention gaps for isothermal runs with the column held at the injection temperature. The broadening is strongly dependent on the linear gas velocity in the retention gap. If the internal diameters of the retention gap and the separation column are similar, the retention gap may have a length exceeding 100 m, even if the separation column is only 10 m long. A 0.5 mm I.D. retention gap attached to a 0.3 mm I.D. separation column (of interest for automatic on‐column injection) may be several meters long. Retention gaps of 0.3 mm I.D. may be used for on‐column injections into separation columns with I.D's. down to about 0.1 mm.
Quantitation of urapidil and its metabolites in human serum by high performance liquid chromatography
Authors: Nieder M. , Dilger C. , Haerlin R. 
Published: May 2005

AbstractThe antihypertensive agent urapidil (Ebrantil Byk‐Gulden, Konstanz) can be reliably quantitated with three metabolites in human serum using high performance liquid chromatography. Serum is alkalinized and extracted with ethyl acetate. The organic phase is back‐extracted with diluted acid. An aliquot is sampled automatically and chromatographed in an optimized combination of mobile and stationary phase. UV‐detection at 273 nm allows a quantitation limit of 5 ng/ml for all analytes. Precise handling of exact volumes facilitates external calibration. The coefficient of variation for spiked samples is less than 5% within and less than 7% between studies. Application of the method to experimental and clinical pharmacokinetic studies of urapidil is illustrated.
Evaluation of conditions for the HPLC determination of plasma amino acids using precolumn derivatization
Authors: Halfpenny A. P. , Brown Ph. R. 
Published: May 2005

AbstractFor the determination of free amino acids in plasma, the conditions for precolumn derivatization of the amino acids and the chromatographic separation were examined. The isoindole products, formed by the reaction of the primary amino acids with orthophthalaldehyde (OPA), were readily separated by RPLC and detected spectrofluorometrically using an excitation wave‐length of 300 nm and an emission cut‐off filter of 440 nm. Since the sensitivity of this method permits determination of amino acids in the femtomole range, the analysis can be performed on samples as small as 10 μl of filtered plasma or serum. The separation is achieved in approximately 35 minutes with good precision for the majority of the amino acids.
Comparative chemical analysis of commercial creosotes and solvent refined coal‐II materials by high resolution gas chromatography
Authors: Wright C. W. , Later D. W. , Wilson B. W. 
Published: May 2005

AbstractThe chemical composition of a commercially available creosote was compared to a direct coal liquefaction product, i.e., solvent refined coal‐II fuel oil blend (SRC‐II FOB) using high resolution gas chromatography (HRGC). In addition, hydrogenated products of these materials were studied. Samples were fractionated by chemical class on neutral alumina. Those fractions previously shown to be the most mutagenic and tumorigenic in laboratory bioassays of coal‐derived materials were analyzed and compared by HRGC and gas chromatography/mass spectrometry (GC/MS). Individual components were tentatively identified and quantitated. Although similar chemical components were present in the creosote and SRC‐II FOB fractions studied, the creosotes had higher concentrations of heavy molecular weight materials and a lower ratio of alkylated to parent polycyclic aromatic compounds than the coal liquefaction products. The creosote samples also had a significantly higher concentration of components which eluted in the polycyclic aromatic hydrocarbon (PAH) chemical class fraction. Amino‐substituted PAH were present in both nonhydrogenated coal liquid and creosote materials. The creosote and SRC‐II FOB crudes and nitrogen‐containing polycyclic aromatic compound (NPAC) chemical class fractions expressed similar microbial mutagenicity. Based on chemical analysis data, the predicted tumorigenic potency of the creosote in laboratory bioassay systems would be equivalent to or greater than the SRC‐II FOB.
Hydrothermal treatment of fused silica capillary columns
Authors: Ogden M. W. , McNair H. M. 
Published: May 2005

AbstractThe activity of fused silica capillary tubing has been shown to vary considerably, which severely influences the reproducibility of column deactivation and inertness. Methods for producing a reproducible, high activity surface with maximum hydroxylation by various hydrothermal treatments were evaluated. Columns pretreated with 20% nitric acid at 200°C for 10 hours, deactivated with D4, coated with OV‐73, and crosslinked with azo‐tert‐butane were found to possess excellent inertness for sensitive analytes such as alcohols, amines, and alkaloid drugs.
Sensitive determination of perfluorocarbon tracers in air by intermediate trapping and GC‐ECD analysis
Authors: de Bortoli M. , Pecchio E. 
Published: May 2005

AbstractThis paper reports on the development of a simple method for the determination of two perfluorinated hydrocarbons (C7F14 and C8F16) in air down to 0.2 ng/m3, for long range atmospheric tracer experiments. The organic vapors are adsorbed on graphitized carbon black, desorbed thermally and determined by capillary GC‐ECD at subambient temperature. Optimization of the experimental conditions is described. The tracers were tested in a field experiment where SF6 was also released and the agreement was satisfactory.
Modification of a packed GC injector to a versatile capillary injector
Authors: Etzweiler F. 
Published: May 2005

AbstractA modification of a packed GC injector to a capillary injector is presented using a simple device which is connected to the GC column by an adsorption‐free connector. It permits injections of large sample volumes up to 500 μl hexane solutions on normal 0.3 mm i.d. capillary columns. No special requirements for the stationary phase are necessary. Involatile residues remain inside the device which can be exchanged easily. High performance of separation and quantification is achieved.
The use of glass and fused silica open tubular columns for the separation of structural, configurational, and optical isomers by selective complexation GC: Sec‐alcohols and ketones
Authors: Schurig V. , Leyrer U. , Weber R. 
Published: May 2005

AbstractThe use of glass and fused silica open tubular columns for selective separation of structural, configurational, and optical isomers (enantiomers) of underivatized aliphatic alcohols and ketones by complexation gas chromatography on optically active metal chelates is described. The method represents a powerful analytical tool for the precise determination of diastereomeric (d.e.) and enantiomeric (e.e.) excesses in asymmetric syntheses and in natural product characterization. The direct screening of the enantiomeric composition and absolute configuration of terpinene‐4‐ol, the aggregation phermone of Polygraphus poligraphus (L), is described.
The effects of modifiers in supercritical fluid chromatography
Authors: Levy J. M. , Ritchey W. M. 
Published: May 2005

AbstractInvestigations have been initiated to examine the basic elements of resolution and how they vary individually and collectively in terms of modifiers used in supercritical fluid chromatography (SFC). Capacity factors (k′) have been determined for a mixture of polynuclear aromatic hydrocarbons from SFC experiments as function of modifier identity and concentration using different stationary phases. Using carbon dioxide as the primary mobile phase, the modifiers investigated included methanol, 2‐methoxy ethanol, 1‐propanol, tetrahydrofuran, dimethyl sulfoxide, acetonitrile, sulfur hexafluoride, and freon 11.
Characterization of Saccharomyces Sp. through determination of amino acid profiles by capillary gas chromatography
Authors: Vasconcelos A. M. P. , Neves H. J. Chaves Das 
Published: May 2005

AbstractThe Saccharomyces strains uvarum, montuliensis, bayanus, capensis and florentinus were grown in liquid media prepared from a 1% aqueous glucose solution to which 0.05% of ammonium sulfate or urea were added as the only nitrogen supply. The amino acids exuded during incubation were isolated by cation exchange and derivatized as the corresponding N,O‐heptafluorobutyryl isopropyl esters. Separation was achieved on a highly deactivated glass capillary column coated with OV‐101. A characteristic amino acid profile was obtained for each of the species studied, allowing the construction of a chemotaxonomic tree, on the basis of present or absent acids.
Automatic system for rapid analysis of volatile compounds by purge‐and‐cold‐trapping/capillary gas chromatography
Authors: Badings H. T. , de Jong C. , Dooper R. P. M. 
Published: May 2005

AbstractA system for automatic analysis of volatile compounds by purge‐and‐cold‐trapping/capillary gas chromatography is described. It is suitable for analysis of volatile compounds in a wide variety of samples, such as water, food products and environmental samples. Possibilities and limitations of the system are evaluated in relation to several parameters. The efficiency of different types of cryogenic trap (open tubular, coated, packed) is also investigated; it depends on purge‐flow rate, temperature of trapping, and total purge volume. Examples of the analysis of volatile compounds in foods and water are given.
Optimum performance of capillary GC columns as a function of tube diameter and film thickness under various operating conditions. Computer program for calculation of H‐ū curves and minimum analysis times
Authors: Leclercq P. A. , Cramers C. A. 
Published: May 2005

AbstractThe Golay‐Giddings and Poiseuille equations are used to derive equations for the calculation of the maximum plate number and minimum time conditions for given columns at fixed, but selectable, outlet pressures. In addition, expressions are presented for the determination of minimum analysis times for separation problems requiring given plate numbers. In this instance, the optimum column length can be calculated as a function of outlet pressure. A Basic computer program, incorporating the equations for the various optima, together with the H‐ū curves, is described. Input variables are either column length or desired plate number, column diameter, film thickness, capacity ratio of the solute, column outlet pressure, seperation temperature, and carrier gas. The carrier gas viscosity is automatically calculated in the case of hydrogen, helium, or nitrogen. For these gases, and if the solute is a n‐alkane, the diffusivity of the solute in the mobile phase is calculated. In this case, the carbon number of the solute is needed in the computation.For high molecular weight polydimethylsilicone phases (e.g. SE‐30), the program can approximate the diffusivity of n‐alkanes in the stationary phase at the given temperature as a function of the carbon number. Of course, manually entered values of viscosity and diffusion coefficients can be included in the calculations.
Synthesis of siloxane stationary phases for capillary gas chromatography and supercritical fluid chromatography
Authors: Ogden M. W. , McNair H. M. 
Published: May 2005

AbstractA comparison is made between dichlorosilanes and cyclic siloxanes as starting materials in the synthesis of stationary phases for capillary gas chromatography (CGC) and supercritical fluid chromatography (SFC). Siloxanes containing one or more of the side groups methyl, vinyl, phenyl, and cyanoethyl in various ratios were synthesized and compared. These phases were characterized by chromatographic (gel permeation, GPC), spectroscopic (IR, 1H NMR, 29Si NMR), and thermal (DSC) methods. Coated fused silica columns were evaluated with respect to polarity, crosslinkability with several free‐radical initiators, and thermal stability. A new liquid phase, 7% cyanoethyl, 7% phenyl, 1% vinyl methyl polysiloxane is shown to be more polar than OV‐1701, more temperature stable, easily crosslinked and suitable for use in supercritical fluid chromatography.
Programmed‐temperture split‐splitless injection of triglycerides: Comparison to cold on‐column injection
Authors: Hinshaw J. V. , Seferovic W. 
Published: May 2005

AbstractThe performance of split and splitless programmed‐temperature (PTV) injection is compared to cold on‐column and hot (classical) split injection for the analysis of triglycerides on an apolar capillary gas chromatographic column. Quantitative accuracy and precision of PTV injection are determined for a synthetic mixture of triglycerides relative to cold on‐column injection.
Rapid analysis using capillary supercritical fluid chromatography
Authors: Wright B. W. , Smith R. D. 
Published: May 2005

AbstractCapillary supercritical fluid chromatography (SFC) is proving to be a viable and useful separation method for thermally labile and nonvolatile materials. As with other capillary chromatographic techniques, very fast separations can be accomplished by sacrificing total efficiency and optimizing the conditions for rapid analysis. This is achieved using short, small‐bore capillary columns, increased mobile phase linear velocities and very fast pressure programming rates. These principles are demonstrated for the rapid separation of selected component systems.
Supercritical fluid chromatography/Fourier transform infrared microspectrometry
Authors: Pentoney S. L. , Shafer K. H. , Griffiths P. R. , Fuoco R. 
Published: May 2005

AbstractThe feasibility of supercritical fluid chromatography/Fourier transform‐infrared (SFC/FT‐IR) microspectrometry is presented. In this approach to SFC/FT‐IR, the chromatographic eluates are aspirated from the restrictor directly onto the surface of a moving window which then passes into the beam focus of an infrared microscope. Because the mobile phase is gaseous at ambient conditions, elimination of the mobile phase is easily accomplished. Detection limits in all interfaces between a chromatograph and an FT‐IR spectrometer in which the mobile phase is eliminated are determined in large part by the area over which the sample is deposited. We have shown that SFC eluates can be condensed at ambient temperature into spots of 100 to 200μm in diameter. The microscope interface therefore serves to increase the sensitivity of the SFC/FT‐IR measurements of these spots and detection limits in the low nanogram range are possible. Preliminary results obtained before any real attempts were made to optimize the deposition process indicate that identifiable spectra can be obtained in real time at the 50 ng level for chromatographic separations performed with a 100μm i.d. wall coated open tubular column. Reproducible reconstructed chromatograms are obtained as each deposited eluate travels through the beam focus of the microscope. The concentration profile of deposited peaks was determined by IR measurements performed at 50 μm increments over the width of the peak to ascertain the deposition size. The results described in this paper, while not yet optimized, indicate the great potential of SFC/FT‐IR microspectrometry.
Mathematical dead time determination and calculation of the constants of the n‐alkane retention time curve on OV polymethyl phenylsilicone stationary phases in gas chromatography
Authors: Touabet A. , Badjah Hadj Ahmed A. Y. , Maeck M. , Meklati B. Y. 
Published: May 2005

AbstractThe column dead time and the constants of the n‐alkane retention time curve in gas‐liquid chromatography are calculated by the Wentworth iterative method on series of OV polymethylphenylsilicones with an increasing percentage of phenyl substituent. The values obtained are in good agreement with those calculated by the methods of Gröbler and Kaiser and with the experimental ones reported in the literature for stationary phases studied at 120°C and 150°C. The scatter of experimental retention times of n‐alkanes and tM and b and c and Kováts retention indices are calculated.
Improvement of a cryogenic preconcentration unit for C2 ‐ C6 hydrocarbons in ambient air at ppt levels
Authors: Schmidbauer N. , Oehme M. 
Published: May 2005

AbstractA previously described method for the quantitative analysis of C2 ‐ C6 hydrocarbons in the ppt range based on cryogenic preconcentration has been improved further. Problems caused by condensation of O2 and traces of water from the sample were overcome using a modified dyring procedure and a tandem preconcentration trap. In addition, the flow path through the unit was simplified further. Technical details are given. The reproducibility of both quantitative results and retention times was improved by these modifications. Typical standard deviations were in the order of 2% at the 200 ppt level.