bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cyclodextrins as chiral stationary phases in capillary gas chromatography. Part III: Hexakis(3‐O‐acetyl‐2,6‐di‐O‐pentyl)‐α‐cyclodextrin
Authors: König W. A. , Lutz S. , Colberg C. , Schmidt N. , Wenz G. , von der Bey E. , Mosandl A. , Günther C. , Kustermann A. 
Published: May 2005

AbstractThe properties of hexakis(3‐O‐acetyl‐2,6‐di‐O‐pentyl)‐α‐cyclodextrin as a chiral stationary phase for capillary gas chromatography are described. For the first time the enantiomers of a series of different lactones are separated and their order of elution is assigned. Moreover, the enantiomers of trifluoroacetylated aldols and amino alcohols, the cyclic carbonates of 1,2‐diols, 1,3‐diols, O‐alkylated glycerols, and some chiral pharmaceuticals are also separated on the new chiral phase. The modified α‐cyclodextrin is stable above 200°C.
Electrochemical, fluorescence, and UV detection for HPLC analysis of various cysteine derivatives
Authors: Ziegler S. J. , Sticher O. 
Published: May 2005

AbstractElectrochemical (ECD), fluorescence (FLD), and UV spectrophotometric (UVD) detection were used to monitor various S‐alk(en)yl‐L‐cysteines and their corresponding sulfoxide isomers following pre‐column derivatization with o‐phthaldialdehyde‐tert‐butylthiol and separation by reversed‐phase HPLC. Recording of hydrodynamic voltammograms, FLD stop‐flow scanning, and on‐line captured UV spectra were methods used for establishing optimal detector settings which were defined as a compromise between favorable selectivity and high sensitivity. Optimal detector settings were found at: (A) 750 mV vs. Ag/AgCl for ECD; (B) excitation at 230 nm and emission at 420 nm for FLD; and (C) 337 nm for UVD. Various aspects of detector practicability such as selectivity, baseline disturbances due to excessive reagent, scanning possibilities, as well as detection limits were evaluated and compared. Minimal detectable amounts of the compounds were in the range of 130‐160 fmol for ECD, and 2.5‐3.5 pmol and 13‐16 pmol for FLD and UVD. In addition, the possibilities and benefits of detector coupling were examined.
Determination of gas phase nicotine and 3‐ethenylpyridine, and particulate phase nicotine in environmental tobacco smoke with a collection bed – capillary gas chromatography system
Authors: Tang H. , Richards G. , Gunther K. , Crawford J. , Lee M. L. , Lewis E. A. , Eatough D. J. 
Published: May 2005

AbstractA combined sampling and analysis technique for the determination of gas phase nicotine and 3‐ethenylpyridine, and of particulate phase nicotine in environmental tobacco smoke with capillary gas chromatography is reported. The major advantage of the technique is that all of the collected particulate phase material is analyzed by thermal desorption of the collected material rather than by analysis of only a fraction of the sample extracted from the collection medium. A Teflon filter microtube is used to collect particulate phase nicotine. This microtube is follwed by a small Tenax sorbent bed to collect gas phase nicotine and 3‐ethenylpyridine. After sampling, the Teflon filter is transferred to a clean glass tube and the tube becomes an insert for a modified packed column injector port where the material collected on the filter is heat desorbed to a cold capillary tubing trap. Gas phase nicotine and 3‐ethenylpyridine are also transferred from the Tenax to the GC column by thermal desorption from the Tenax sorbent bed. Gas phase nicotine and 3‐ethenylpyridine, and particulate phase nicotine are each determined by GC analysis of the desorbed material. Nicotine and 3‐ethenylpyridine are quantitated by the use of external standards. This technique is straightforward and can be used for semi‐real time determination of both gas and particulate phase compounds in environmental tobacco smoke. The results obtained by this technique compare well with those obtained by sampling with annular diffusion denuders.
Determination of extracolumn effects in recycle gas chromatography with capillary columns
Authors: Roberts D. , Bertsch W. 
Published: May 2005

AbstractExtracolumn band broadening in multidimensional systems utilizing flow switching is clearly undesirable. In certain cases, i.e. capillary recycle gas chromatography, the success of an experiment is contingent on the minimization of pre‐ and post‐column dispersion of the peaks. Knowledge of these sources of peak distortion is necessary to optimize the experimental design. A system that extracts statistical parameters from real chromatographic peaks is discussed and used to evaluate band broadening in a capillary recycle experiment.
The influence of evaporative dynamics on precision in split capillary GC
Authors: Bowermaster J. 
Published: May 2005

AbstractThe kinetics of sample evaporation was studied for four common injection liners at various temperatures. The rates of solvent and sample evaporation were measured. The sample distribution at the split point was probed by inserting two capillary columns in one injector. Greater homogeneity at the split point corresponded to higher precision (better correlation between the sample and internal standard peak areas). Evidence of aerosol formation using inverted cup inlet liners was seen. Packed column precision was better than capillary precision in each case, i.e., using straight split liners, inverted cup liners, and cold on‐column injection. Capillary precision is best when the sample and internal standard elute close together, and may be improved by using solvents that vaporize slowly.
Micro‐HPLC/TLC/FTIR
Authors: Fujimoto C. , Morita T. , Jinno K. , Shafer K. H. 
Published: May 2005

AbstractIdentification problems often encountered in high performance liquid chromatography (HPLC)/Fourier transform infrared spectrometry (FTIR) can be circumvented through the use of a thin‐layer chromatographic (TLC) plate as deposition and infra‐red sampling medium. The combination of complementary separation modes is shown to demonstrate increased resolution of the components of complex mixtures. In this particular work, the effluent from a reversed‐phase microcolumn is continuously deposited on a TLC plate with alumina stationary phase. The solute remains on the plate as a continuous record of the HPLC separation, which is then analyzed by diffuse reflectance FTIR. When the HPLC separation is inadequate for full separation of the components, the immobilized HPLC chromatogram serves as a starting point for subsequent TLC separation. A number of FTIR reconstructed chromatograms and spectra which are derived from the TLC plate aid in the interpretation.
High speed analysis of underivatized drugs by gas chromatography–mass spectrometry
Authors: Kokanovich J. D. , Simonick T. F. , Watts V. W. 
Published: May 2005

AbstractThe technique of choice for many types of forensic drug confirmations is gas chromatography/mass spectrometry (GC/MS). Significant amounts of analytical time can be involved in a GC/MS run. The use of a 0.1 mm i.d. fused silica capillary column with hydrogen carrier gas can significantly increase the speed of an analysis without sacrificing resolution. Nanogram levels of underivatized drugs, from amphetamine to strychnine, can be eluted in less than twelve minutes. The multitasking system permits data acquisition, while performing data reduction on the previous run.
Injector chambers for classical GC splitless injection must be large!
Authors: Grob Konrad , Biedermann Maurus 
Published: May 2005

AbstractInjector overflow is determined quantitatively by analysis of the septum purge effluent. Vaporizing chambers must have an internal volume of about 1 ml (e.g. 80 × 3.6 mm i.d.). This allows splitless injection of volumes between 1 and 2.5 μl, depending on the solvent. The septum purge should be closed during splitless transfer to prevent losses by back‐diffusion.
Analysis of pyrethrins using capillary supercritical fluid chromatography and capillary gas chromatography with fourier transform infrared detection
Authors: Wieboldt R. C. , Kempfert K. D. , Later D. W. , Campbell E. R. 
Published: May 2005

AbstractThe six insecticidally active components in a commercial preparation of pyrethrin extract are separated by capillary gas chromatography (GC) and by capillary supercritical fluid chromatography (SFC). Thermal degradation of pyrethrin I and II are observed under the GC conditions required to separate the pyrethrin components. The use of shorter columns and thinner stationary phase coatings reduce the amount of degradation but cannot eliminate degradation of pyrethrin II. The SFC chromatograms, obtained under thermally mild conditions, show that all components including pyrethrin II elute without degradation. Infrared spectra of cinerin I & II, jasmolin I & II, and pyrethrin I & II are obtained using a flow through SFC/IR detection cell. Spectra clearly reveal the structural differences needed to distinguish and identify the components in the extract.
Quantitation in miniaturized GC and SFC systems
Authors: Schomburg G. , Behlau H. , Häusig U. , Hoening B. , Roeder W. 
Published: May 2005

AbstractSeparations of high efficiency and/or speed can be achieved in capillary GC by capillary columns of lower internal diameter (< 50 μm). Sampling techniques for the analytical application of narrow bore fused silica columns have been evaluated with regard to quantitation. On‐column injection cannot be applied. Therefore liquid samples have to be vaporized in external devices before they enter the chromatographic system. Sample introduction by syringe with subsequent splitting must and can be applied but requires special syringes with perfect piston sealing because of the high inlet pressures needed even with hydrogen as carrier gas. For general analytical applications, valve systems should be developed to eliminate both the syringe and the septum from instrumental GC set‐up's.In SFC using either narrow bore capillary or packed microbore columns, time‐controlled valve sampling with partial displacement of the sample from the loop seems to be an adequate technique because of the very high inlet pressures involved. Splitting in combination with valve operation can also be applied in capillary SFC at least to samples of good solubility in the mobile phase. A disadvantage of splitting in SFC is that another restriction for the adjustment of the split flow is necessary.
The computer‐aided optimization of capillary columns for minimum time analysis and minimum detectabiliy
Authors: Villalobos R. , Annino R. 
Published: May 2005

AbstractA model utilizing the extended Golay‐Giddings equation, with an added term that expresses the instrumental contributions to the plate height, has been tested and found to accurately predict the chromatograph's output for a given set of operating conditions. The model forms the basis of a computer program that will recommend the length of column (of a specified inside diameter and film thickness) to be used (at a given temperature and input pressure) to obtain a minimum time analysis of the most difficult to separate pair of the mixture. Alternative solutions are available that specify the length of column, operating pressure, and the maximum permissible sample size required to provide a minimum analysis time for a system with specified minimum detection limits.
Quantitative determination of oxocarboxylic and hydroxycarboxylic acids in normal individuals and ketoacidotic patients
Authors: Liebich H. M. , Dotzauer A. 
Published: May 2005

AbstractOxo‐ and hydroxycarboxylic acids as metabolites of valine, leucine, and isoleucine and of ketogenesis are simultaneously quantitated in the form of their methyl esters and methyl esters/O‐methyloximes by gas chromatography using internal and external standards. Normal values for the urinary excretions of the amino acid metabolites are between 3 ± 2 μmol/24 h (mean value ± standard deviation) for 2‐oxoisocaproic acid and 122 ± 58 μmol/24 h for 3‐hydroxyisobutyric acid. In diabetic ketoacidosis the values are increased by a factor of 2‐10.
Inner wall coating of micro‐LC columns. Wall effects in LC
Authors: Verzele M. , Dewaele C. , De Weerdt M. , Abbott S. 
Published: May 2005

AbstractAn elastic inner wall coating in the fused silica capillaries used for Micro‐LC (LC on packed fused silica capillary columns) stabilizes the packed bed and thus increases column efficiency and life expectancy. Probably the particles of packing material are partly forced into the elastic polymer layer which thus holds the packing in position. Bonded polymers of very different chemical polarity can be used with equally good results. Variation of the coating layer thickness shows that there is an optimum value around 0.3 μm. A discussion of various wall effects in LC columns is presented. The i.d. of the columns is a most important parameter in this respect.
Analysis of the headspace of foodstuffs near room temperature
Authors: Kallio H. , Leino M. , Salorinne L. 
Published: May 2005

AbstractFormation of volatiles in onion varieties, aging of coffee, and the quality of birch syrup were studied by using near room temperature headspace GC‐MS analysis. Accurate volumes (1–500 mL) of the gaseous samples were introduced into the capillary column either by a syringe or by sucking with a pump. The standard deviation of the contents was typically 1‐7% depending on the foodstuff and the compound. The ratio of 2,3‐butanedione to 2‐methylfuran decreased during the storage of coffee and was a typical measure of aging. Analysis of even the very polar 2,5‐dimethyl‐4‐hydroxy‐3(2H)‐furanone in the headspace of birch syrup was possible. The distribution patterns of the sulfur‐containing volatiles generated by crushed onions were close to each other in different varieties. The rate of the total formation of the compounds varied from cultivar to cultivar.
Systematic investigation of enantiomer resolution of N‐pivaloyl derivatized amino acid esters. Preparation of glass capillary columns coated with the chiral phase XE‐60‐L‐val‐pea
Authors: Aichholz R. , Fischer P. 
Published: May 2005

AbstractA laboratory working procedure is described for silanization of glass capillaries with bis(cyanopropyl)tetramethyldisiloxane, prior to coating with XE‐60‐L‐valine‐(S)‐α‐phenylethylamide as chiral stationary phase. GC columns thus prepared exhibit good inertness and no long‐term deterioriation of enantioselectivity up to 220°C. A general procedure is given for derivatization of simple and of polyfunctional amino acids, in a batch mixture, simultaneously, and completely at both the N‐ and the C‐terminus and all other protic functions. Within the seven series of N‐pivaloyl amino acid esters tested (methyl to neopentyl), baseline separation is obtained for all R/S pairs, including the proline derivative.
Detection of C, H, N, and O in capillary gas chromatography by atomic emission
Authors: Sullivan J. J. , Quimby B. D. 
Published: May 2005

AbstractUsing a new atomic emission detector for gas chromatography, the quantitative and qualitative aspects of selective elemental detection of carbon, hydrogen, nitrogen, and oxygen were investigated. Sensitivity, precision, degree of tailing, and response variation between compounds are reported for capillary applications.Earlier atomic emission detectors reported poor sensitivity and selectivity for the analysis of oxygen. These problems have been greatly reduced due to lower interactions between elements in the sample and the silica wall of the water‐cooled discharge tube.Using near‐optimal sample amounts and chromatographic conditions, area precision was found to be very good with little variation in response factors among different compounds. For the compounds tested, response factors varied over a span of 2% to 3% for carbon, hydrogen, and nitrogen, and over 7% for oxygen. For quantitative analysis, area ratios were calibrated directly from the area ratios of two elements of an internal standard, and yielded better precision and compound independence than the individual calibrated response of each element.Empirical formulas were calcualted using one peak as a qualitative internal standard. Unambiguous formulas were determined for some, but not all, of the compounds tested. Further increases in precision and/or compound independence is needed before empirical formula determination can be used as a routine tool.
Use of xenon as a mobile phase for on–line capillary supercritical fluid chromatography–fourier transform infrared spectrometry
Authors: Raynor M. W. , Shilstone G. F. , Bartle K. D. , Clifford A. A. , Cleary M. , Cook B. W. 
Published: May 2005

AbstractXenon is investigated as a mobile phase for on‐line capillary supercritical fluid chromatography‐Fourier transform infrared spectrometry (SFC‐FTIR). Polycyclic aromatic hydrocarbons, aromatic isocyanates, and epoxy acrylate oligomers are analyzed as examples to show that xenon has similar selectivities and solvating powe to CO2. Its optical transparency makes it ideal for IR detection. A stop flow system is constructed to increase the sensitivity of spectra measured from compounds which are weak IR absorbers.
Extending the scope of enantiomer separation on diluted methylated β‐cyclodextrin derivatives by high‐resolution gas chromatography
Authors: Nowotny H.‐P. , Schmalzing D. , Wistuba D. , Schurig V. 
Published: May 2005

AbstractHigh‐resolution open‐tubular columns coated with solutions of heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin (Phase I) or heptakis(2,6‐di‐O‐methyl‐3‐O‐trifluoroacetyl)‐β‐cyclodextrin (Phase II) in moderately polar polysiloxanes such as OV‐1701 (5% cyanopropyl/7% phenyl/88% methylpolysiloxane) and OV‐225 (25% cyanopropyl/50% phenyl/25% methylpolysiloxane) are used for the gas chromatographic enantiomer separation of volatiles belonging to different classes of compounds. No derivatization procedures are necessary for most of the resolved chiral molecules. The chiral stationary phases can be operated between 25 and 190°C for extended periods of time. The enantiomer separation of saturated, unfunctionalized hydrocarbons clearly demonstrates the importance of molecular inclusion in chiral recognition using cyclodextrins for this class of compounds. The different, and in some cases complementary, selectivity of the Phases I and II is demonstrated.
Capillary column SFC instrumentation based on piston pumps with a programmable back‐pressure regulator for on‐line mixing of mobile phases
Authors: Anton K. , Pericles N. , Widmer H. M. 
Published: May 2005

AbstractAn alternative phase delivery system based on piston pumps and a back‐pressure regulator has been developed for capillary column SFC. The chromatography is not affected by the fast piston pump refill. A homogeneous on‐line mixing of binary phases with simultaneous pressure programming is easily accessible without any additional computing. Acceptable reproducibilities (< 3.5% RSD for external and < 2.0% RSD for internal standard methods) were found with mixtures of 2‐propanol/CO2 as mobile phases using UV detection and split ratios of 1:60 and 1:120. Variation and control of the split are easily done by simple flow rate volumetric changes.
An automated large volume on‐column injection technique for capillary gas chromatography
Authors: McCabe T. , Hiller J. F. , Morabito P. L. 
Published: May 2005

AbstractAutomated large volume (25‐200 μl) on‐column injections into a gas chromatograph with a capillary column were successfully performed by coupling a retention gap technique with an air actuated rotary valve. The linearity, injection precision, and carryover were evaluated. Slight boiling point discrimination was observed. This technique is compatible with commonly used chromatographic detectors (FID, ECD, MS) and conditions, while requiring very little instrument modification. The work is directed at the eventual reduction of manpower and turnaround time for sample collection and extraction, and Kuderna‐Danish concentration when dealing with methods similar to EPA 625.
A new method for in situ crosslinking of stationary phases on fused silica capillary columns
Authors: Liu Huwei , Zhang Aiqing , Jin Yonghao , Fu Ruonong 
Published: May 2005

AbstractA new mixed crosslinking agent composed of dicumyl peroxide and tetra(methylvinyl)cyclotetrasiloxane was used to prepare fused silica capillary columns with in situ crosslinked stationary phases including PEG‐20M, SE‐54, and OV‐1. These columns proved to have good thermostability and inertness. As examples of potential applications a mixture of isomers of nitrotoluene and dinitrotoluene, and pyrolyzates of polystyrene were separated by using these columns.
HPLC determination of valproic acid in human plasma by derivatization with O‐p‐nitrobenzyl‐N,N′‐diisopropylisourea
Authors: de Illiano B. Gentile , de Gainzarain A. Quintana 
Published: May 2005

AbstractA sensitive and specific method for the determination of valproic acid in plasma has been developed. After the proteins in the plasma have been precipitated with a saturated solution of ammonium sulfate in 1N HCl, the valproic acid, together with the internal standard, is extracted from the plasma with dichloromethane.An aliquot of the organic solution is taken for derivatization of the valproic acid and the internal standard with O‐p‐nitrobenzyl‐N,N′‐diisopropylisourea.Separation is carried out by HPLC using two chromatographic systems: an adsorption system with a μ Porasil column, hexane‐chloroform (94:6) as mobile phase, and caproic acid as internal standard and a partition reverse phase system comprising a μ Bondapak TM/C18 column, acetonitrile/methanol/0.0035 M phosphate buffer (60:10:30), and caprylic acid as internal standard. UV detection is at 254 nm.This method, developed in both systems, permits the determination of plasma levels of valproic acid in the reported range of 50‐100 μg/mL. With adequate sensitivity, specificity, precision, and accuracy.The plasma levels of valproic acid may be determined by this method without interference from the commonest antiepileptic drugs. Good correlation is obtained with the enzymatic immune analytic method: EMIT.
A fundamental study of the effects of modifiers in supercritical fluid chromatography
Authors: Janssen J. G. M. , Schoenmakers P. J. , Cramers C. A. 
Published: May 2005

AbstractThe effects of organic modifiers on retention and peak shape in packed‐column supercritical fluid chromatography were studied. The adsorption behavior of different modifiers was investigated on stationary phases consisting of hydrocarbon monolayers chemically bonded on silica. Adsorption isotherms for several modifiers were recorded using breakthrough measurements. The results were compared with those obtained by a simple method based on the injection of different sample sizes. Modifiers were selected to reflect various types of interactions with the silica support. Isotherms were found to be approximately Langmuirean. Experiments were performed to elucidate the influence of adsorbed molecules on the retention of selected test solutes.The introduction of a solvent modifier can lead to a substantial change in the mobile phase density, the effect of which is comparable with that of an increase in the density of pure carbon dioxide. Our results confirm that the effects of low concentrations of modifiers (between 0 and 2 percent) in packed‐column SFC are largely due to deactivation of residual silanol groups on the silica support. The accessibility of the active sites was found to depend strongly on the size and structure of the modifier molecules. The decrease of retention due to the addition of low concentrations of modifiers could be described accurately by a model derived from Langmuir adsorption behavior. Some semi‐quantitative rules for the selection of modifiers and the required concentrations for optimum deactivation of the support are discussed.