bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solvent gradient elution in micro HPLC
Authors: Ishii D. , Hashimoto Y. , Asai H. , Watanabe K. , Takeuchi T. 
Published: May 2005

AbstractA simple gradient method for capillary column and micro high performance liquid chromatography using either single or multiple mixing chambers is presented. The gradient profile is dependent on the number of the mixing chambers. This system permits solvent gradient elution at flow rates less than 10 μl/min with satisfactory reproducibility.
Retention in capillary supercritical fluid chromatography
Authors: Chester T. L. , Innis D. P. 
Published: May 2005

AbstractSupercritical fluid chromatography (SFC) sometimes exhibits GC‐like behavior and sometimes LC‐like behavior, depending on conditions. However, it is not always clear whether one of these types of behavior, or a combination, operates for a particular set of conditions for every solute in a mixture. For example, some components may be partitioned mostly by their vapor pressures, while others, in the same mixture, are partitioned predominantly by solvent‐like properties of the mobile phase.Plots of retetion (as log of the capacity factor) vs. reciprocal temperature at constant pressure reveal a clear change in the character of the separation of well‐behaved solutes. A thermodynamic explanation of the observed behavior is given, based on the assumption that partitioning is controlled by the heats of solution of solute in the mobile and stationary phases. A model of SFC retention as it deviates from pure‐GC behavior on the same column is presented.
Quantitation in capillary gas chromatography with emphasis on the problems of sample introduction
Authors: Schomburg G. , Häusig U. , Husmann H. 
Published: May 2005

AbstractSampling techniques for practical quantitative capillary GC have to meet certain principal requirements. Both the absolute and the relative peak areas (e.g. column loads) must be reproducible with high precision and at high accuracy; discrimination of certain constituents according to their volatility should not take place on sampling. On the basis of systematic studies, the three most reliable sampling techniques used for GC analyses with the aim of achieving precise and accurate quantitative data proved to be the following: On‐column, injection, splitless PTV injection, and an optimized version of split sampling called “cooled needle split” injection. The on‐column technique can be optimized by using precolumns with wider internal diameters and without stationary phase coatings to overcome the problems of large liquid sampling volumes and for automation. The PTV technique should only be used in the splitless mode because discrimination cannot be suppressed completely with the split mode. All three of the techniques can be operated automatically, either to avoid “human interference”, i.e. to improve precision or for unattended operation to save man‐power.
Application of the “cooled needle” technique to split and splitless sampling onto capillary columns
Authors: Schomburg G. , Häusig U. 
Published: May 2005

AbstractCooled needle sampling using syringes was applied to splitless injection and to simulated distillation analyses. Slight changes of the construction of the previous device are also described. The changes concern the temperature profile within the injector and especially the vaporization insert. Even with the low carrier gas flow through the injector during splitless injection, discrimination by component volatility can be avoided. Precision and accuracy of simulated distillation data obtained with split sampling also can be improved by the cooled needle technique.
Dramatic selectivity changes on carrier gas flow change in a series‐coupled GC capillary tandem
Authors: Kaiser R. E. , Rieder R. I. , Leming Lin , Blomberg L. , Kusz P. 
Published: May 2005

AbstractWe describe the polarity of selectivity of a GC separation system in terms of Retention Index data. In a series‐coupled capillary system having stationary phases of differing polarity even slight (independent!) carrier gas flow changes in one part of the capillary series result in a dramatic change of selectivity. “Dramatic” is a relative term! Using a simple electronically controlled flow changing device we found retention index changes of several hundred units for polar test compounds such as phenols on a SE30/Carbowax tandem. This means: The classical theoretical model for understanding retention (and selectivity) in chromatography must be corrected. We propose a very simple approach involving addition of the expression RESIDENCE TIME to the chromatographic vocabulary. Instead of using flow resistors, one can just add a pressure regulator to the coupling point. A powerful analytical concept is now in easy reach.
Analysis of petroleum fractions by on‐line micro HPLC‐HRGC coupling, involving increased efficiency in using retention gaps by partially concurrent solvent evaporation
Authors: Munari F. , Trisciani A. , Mapelli G. , Trestianu S. , Grob K. , Colin J. M. 
Published: May 2005

AbstractTwo‐dimensional chromatography of gasoline by on‐line coupled HPLC‐HRGC, as described in this paper, allows separate GC analysis of paraffins and aromatics. The GC system contains a retention gap of only 10 m length for introducing HPLC fractions of 100 μl volume. This becomes possible through evaporation of part of the solvent during introduction of the HPLC eluent. This “partially concurrent solvent evaporation” technique allows transfer of large volumes of HPLC eluent into relatively short retention gaps, maintaining the full efficiency of the solvent effects in reconcentrating the bands of the early eluted solutes.
Temperature programmed retention indices: Calculation from isothermal data. Part 1: Theory
Authors: Curvers J. , Rijks J. , Cramers C. , Knauss K. , Larson P. 
Published: May 2005

AbstractDirect conversion of isothermal to temperature programmed indices is not possible. In this work it is shown that linear temperature programmed retention indices can only be calculated from isothermal retention data if the temperature dependence of both the distribution coefficients and the column dead time are taken into account.Procedures are described which allow calculation of retention temperatures and from these, accurate programmed retention indices. Within certain limits the initial oven temperature and programming rate can be chosen freely. The prerequisite for this calculation is the availability of reliable isothermal retention data (retention times, retention factors, relative retention times, or retention indices) at two different temperatures for one column.The use of compiled isothermal retention indices at two different temperatures for the calculation of retention temperatures and thus temperature programmed indices is demonstrated. For the column for which programmed retention indices have to be determined, the isothermal retention times of the n‐alkanes and the column dead time as a function of temperature have to be known in addition to the compiled data for a given stationary phase.Once the programmed retention indices have been calculated for a given column the concept allows the calculation of temperature programmed indices for columns with different specifications. The characteristics which can be varied are: column length, column inner diameter, phase‐ratio, initial oven temperature, and programming rate.
Dynamic headspace enrichment system for CGC analysis of volatiles released by plants
Authors: Termonia M. , Alaerts G. 
Published: May 2005

AbstractThe aim of the present study is to develop a method for following the changes in the chemical composition of volatile substances released by plants. Dynamic headspace enrichment, followed by on‐line thermal desorption and cryotrapping was coupled with capillary gas chromatography. The technique was optimized by adjusting the sampling and desorption parameters and by designing a special condensing device to avoid the transfer of excessive amounts of water into the analytical column. Details are given for the characterization of volatiles compounds released by mosses.
Micro‐HPLC 1: Linear “breakthrough‐gradients” using the discontinuous interface between eluents in a packed gradient‐generator column
Authors: Berry V. , Ishii D. , Takeuchi T. 
Published: May 2005

AbstractA new approach is described for micro‐HPLC for generating nearly linear gradients in the 40 to 550 μl volume range. These “linear” gradients have a straight line middle portion with a gentle curved onset of the gradient andd rapid attainment of the final 100% composition. Such “breakthrough‐gradients” are produced by the interface between weak and strong eluent when a small (3 × 0.46 cm) packed “gradient‐generator” column is switched abruptly from weak to strong eluent. The model system described here, without an analytical column, shows gradients from weak eluent (water) to strong eluent (modele with water plus acetone) using a 12‐port high pressure valve to 1) vent the “flush” eluent, and simultaneously 2) begin the gradient and 3) make the sample injection.The volume of the gradient can be changed in two ways. If the breakthrough‐generator is packed with very large (300 to 1600 μm nonporous particles, the gradient volume is nearly independent of the flush flow rate. The flush flow is used to quickly move the breakthrough‐interface to the head of the micro‐HPLC column. However, the gradient volume can be increased by using larger solid particles in the gradient‐generator column because of increased eddy diffusion. If the gradient‐generator is packed with porous particles (75–150 μm), the gradient volume can be changed over a broad range by simply changing the flush flow rate. This simple control over the gradient volume is due to the increased mass transfer of weak eluent out of the porous particles into the strong eluent at higher flush flows.The breakthrough‐interface gradient‐generator column approach provides the following advantages for micro‐HPLC:

– Gradient volumes can be readily varied over the micro‐HPLC range 40–550 μl.

– Gradient are linear with smooth and rapid onset of intial and final concentrations.

– Gradient are produced inexpensively with a single high‐pressure precision pump.

– Gradient can be automated with a timer and single 12‐port valve that provides both column regeneration and sample injection.
A study of some deactivation methods for fused silica capillary columns by CP‐MAS NMR and capillary gas chromatography
Authors: Rutten G. , de Haan J. , van de Ven L. , van de Ven A. , van Cruchten H. , Rijks J. 
Published: May 2005

AbstractThe effect of deactivating a fused silica surface by silylation with 1,1,3,3‐tetraphenyl‐1,3‐dimethylilazane (TPDMDS), triphenylsilylamine (TPSA), and octamethylcyclotetrasiloxane (D4) and by polydimethylsiloxane degradation (PSD) is studied. Rehydrated, dried, and deactivated Cab‐O‐Sil M5 samples are used as model materials for 29Si CP‐MAS NMR analysis.At about 350 °C, TPDMDS yelds mainly diphenylmethylsiloxysilane, dimethyldisiloxysilane, and triphenylsiloxysilane groups. TPSA yields phenyltrisiloxysilane, diphenyldisiloxysilane, and triphenylsiloxysilane groups. At 400°C, the products formed initially are eventually replaced by methyltrisiloxysilane or phenyltrisiloxysilane groups, while a substantial number of silanol groups still remains. The possible consequences for wettability are discussed.D4 reacts with Cab‐O‐Sil even at 200°C, but a large number of silanol groups remains. This number decreases gradually at higher temperatures and becomes negligible above 400°C. The formation of methyltrisiloxysilane groups, which starts at 425°C, is predominant at 490°C.
Loss of water during heat treatment of acid leached glass and fused silica capillary columns
Authors: Venema A. , Sukkel J. T. 
Published: May 2005

AbstractA study was carried out on the effects of acid leaching of capillary column wall materials. Leaching experiments with glass and fused silica were performed under static and dynamic conditions; moreover, the influence of the temperature was investigated. The amount of water released during different temperature programs was measured with a microwave plasma detector. Different leaching conditions and column wall materials cause considerable variations in water production. These results probably explain the disappointing deactivation efficiency obtained for fused silica and dynamically leached soft glass if HMDS is used. Evidence was found for an increase in surface area due to acid leaching.
A study in high‐temperature silylation of silica
Authors: Welsch T. , Frank H. 
Published: May 2005

AbstractHigh‐temperature silylation (HTS) used for the deactivation of capillary columns was studied on the silica commonly used in HPLC to gain a better insight into this process. LiChrosorb Si 100 was silylated with disilazanes at different temperatures and the materials obtained were compared in terms of organic and silanol group surface concentration, IR reflection spectra, HPLC behavior, and pore distribution parameters. Applying diphenyltetramethyldisilazane, the volatile reaction products were monitored during the HTS process. With increasing silylation temperature up to 400°C the silanol surface concentration is reduced to a very small level independent of the organic group concentration which exhibits a broad maximum depending upon substituents and temperature. Up to 350°C triorganosiloxy groups prevail as bonded organic groups. It could be proved that HTS is accompanied by pore alterations of the silica matrix. Arguments proposed by different authors in explaining HTS effects are discussed.
A new bonded stationary phase for the gas chromatographic separation of volatile priority pollutants and chlorinated pesticides
Authors: Mehran M. F. , Cooper W. J. , Lautarno R. , Freeman R. R. , Jennings W. 
Published: May 2005

AbstractA new phenyl‐cyanopropyl polymethylsiloxane stationary phase, DB‐1301, which can be crosslinked and bonded to the fused silica surface, has been synthesized. The phase composition was optimized for the separation of 18 volatile priority pollutants, selected from the so‐called “purgables” list because of problems associated with their resolution. The composition of the stationary phase was based on theoretical considerations of binary phase mixtures and window diagram prediction. Columns coated with this stationary phase are compatible with atom selective detectors, such as the electron capture detector. A mixture of 18 volatile priority pollutants and a mixture of chlorinated pesticides were used as test probes on a prototype 30 m × 0.32 mm fused silica column, containing a 1.0 μm film of DB‐1301.
Gas chromatographic – mass spectrometric analysis of compounds generated upon thermal degradation of some stationary phases in gas chromatography – Part II
Authors: Schmidt S. , Hoffmann S. , Blomberg L. G. 
Published: May 2005

AbstractThe applicability of capillary columns for gas chromatography is often limited by stationary phase degradation at elevated temperatures. In order to achieve a better understanding of column thermostability, column bleed products have been analyzed qualitatively by gas chromatography‐mass spectrometry (GC‐MS). Three silicone stationary phases were studied: SE‐52, SE‐54, and OV‐1701. Each of these was immobilized in the columns. The proportion of cyclics containing diphenyl in column bleed from SE‐52 reflected to a large extent the composition of the polymer, while for SE‐54 the proportion of such cyclics was unexpectedly high. The polar moiety of OV‐1701, the cyanopropyl(phenyl)siloxy unit, was found to exert a highly destabilizing effect on the polymer, and the thermal degradation products consisted mainly of cyclosiloxanes containing this unit.
Application of chemometrics in homolog‐specific analysis of polychlorinated biphenyls
Authors: Onuska F. I. , Mudroch A. , Davies S. 
Published: May 2005

AbstractA principal components multivariable statistical method based on SIMCA 3B (Soft Independent Method of Class Analogy) algorithms was evaluated and applied to interpretation of homolog‐specific analysis of polychlorinated biphenyls by high resolution gas chromatography. High resolution gas chromatograms can be evaluated in high resolution separations of individual PCB isomers and grouped into the homologous series. The chromatograms show distinct differences between PCB compositions with different contents of chlorine atoms in technical mixtures (Aroclors). The objective of utilizing SIMCA 3B was its evaluation for a possible identification, classification, and categorization of Aroclors in environmental samples.
Determination of bile acids and lysolecithin in artificial and natural gastric juice by HPLC for characterization of antacida
Authors: Nieder M. , Jaeger H. , Guthauser U. , Althaus B. 
Published: May 2005

AbstractWork‐up procedures and HPLC separation systems for determination of taurocholic, glycocholic, chenodeoxycholic, and cholic acids and lysolecithin in artificial and natural gastric juice are described. These compounds are used for testing the binding capacity of antacida to the individual analytes. Work‐up is simple, no extraction or filtration being required. The optimized combinations of stationary and mobile phases allow selective and sensitive determination of the respective bile acids in gastric juice. For optimization, the capacity factors of two related bile acids were evaluated for numerous commercial stationary phases. The mechanism of retention is different for free and conjugated bile acids. Special aspects of routine analysis are discussed.
Characterization of Pygeum africanum bark extracts by HRGC with computer assistance
Authors: Martinelli E. M. , Seraglia R. , Pifferi G. 
Published: May 2005

AbstractThe components of Pygeum africanum bark extracts, used for the treatment of benign prostatic hypertrophy, were characterized by high resolution gas chromatography (HRGC) and mass spectrometry (MS). Among various compounds n‐docosyl trans‐ferulate was identified and quantitated by HRGC as a derivative of n‐docosanol, which is considered to be one of the active components of the extract. The origin of different Pygeum a. extracts can be studied by eigenvector projection of HRGC profiles with computer assistance.
Study of protein association and micelle formation in surfactants by microcolumn exclusion chromatography
Authors: Zimina T. M. , Maltsev V. G. , Belenskii B. G. 
Published: May 2005

AbstractThe application of microcolumn exclusion chromatography to the determination of equilibrium and kinetic association constants for proteins is described. Taking phospholipase A2 as an example, the relationship between association and enzymatic activity was investigated. A procedure for determination of the critical concentration of micelle formation (CCM) in surfactants was developed.
Evaluation of a thermionic detector for capillary supercritical fluid chromatography of nitrated polycyclic aromatic compounds
Authors: West W. R. , Lee M. L. 
Published: May 2005

AbstractA thermionic detector was evaluated for capillary supercritical fluid chromatography of polar nitro‐containing polycyclic aromatic compounds (nitro‐PAC). Three modes of detector operation were studied. The best performance was obtained using a nitro‐selective mode of detection. Although linearity was confined to a narrow range for a given source current, the sensitivity was excellent; 20 pg injected for p‐nitrophenol gave a signal‐to‐noise ratio of 3. Conventional thermionic detection also produced good sensitivity; however, serious baseline drift was observed at high operating temperatures using density programming. A third mode, flame thermionic detection, was not acceptable because of low sensitivity. A number of nitro‐PAC were successfully chromatographed using density programming at 101°C. Hydroxynitropyrenes, nitropyrene quinones, and 9‐hydroxy‐2‐nitrofluorene, which could not be eluted in capillary gas chromatography, were successfully chromatographed here. Retention of these compounds increased sequentially on 50% n‐octyl‐, 5% phenyl‐, and 25% biphenyl polysiloxane stationary phases, respectively. Stationary phase interactions appeared to be more a function of the polar functional groups on the aromatic rings than of the hydrocarbon character of the compounds. Solute solubility in the mobile phase and volatility were additional factors contributing to the elution of these molecules. Finally, these results were used to identify a number of nitro‐PAC in a polar subfraction of a diesel particulate extract.
Capillary supercritical fluid chromatography of archaebacterial glycerol tetraether lipids
Authors: DeLuca S. J. , Voorhees K. J. , Langworthy T. A. , Holzer G. 
Published: May 2005

AbstractThe analysis of bacterial glycerol tetraethers by capillary supercritical fluid chromatography is described. Complete separation of ethers, differing only by the number of cyclopentane rings present in the isopranyl side chains could be achieved. On a 50% methylphenylpolysiloxane coated capillary, the ethers eluted in the order of increasing cyclopentane content. The analysis revealed the presence of two previously unreported structural isomers of glycerol tetraethers. The method can be used qualitatively and quantitatively as a fast and sensitive screening test for such compounds in living organisms and sedimentary organic matter.
A linear relationship between partition ratio and composition of a binary mobile phase in reversed‐phase liquid chromatography using chemically bonded stationary phases
Authors: Jaroniec M. , Jaroniec J. A. 
Published: May 2005

AbstractA simple linear relationship which enables the effect of the composition of a binary mobile phase on the retention of a solute to be assessed in reverse phase liquid chromatography using a bonded stationary phase has been derived. The equations have been tested using published experimental data.
Stationary‐phase focusing in capillary gas‐liquid chromatography: Enhancement of the maximum permissible sample size
Authors: Pretorius V. , Lawson K. 
Published: May 2005

AbstractEquations have been derived to predict the extent to which the sample size may be increased, without decreasing the column performance, by stationary‐phase focusing at sub‐ambient temperatures. Under favorable circumstances the sample size may be enhanced several hundredfold.
Stationary‐phase swelling and its consequences in capillary gas‐liquid chromatography
Authors: Pretorius V. , Lawson K. 
Published: May 2005

AbstractSample introduction using the solvent effect can lead to significant swelling of the stationary phase. The phenomenon has been studied theoretically and experimentally. The longitudinal profile of the swollen phase has been established. Swelling can affect the retention time of solutes, the shape of solute bands emerging from the inlet, and the maximum permissible sample size.
A study of thermal peak splitting in capillary GC
Authors: Reed G. D. , Hunt R. J. 
Published: May 2005

AbstractFluctuating thermal gradients are recognized as a distinct source of peak splitting in capillary column gas chromatography. In this study, the influence of analyte signal level, temperature oscillation amplitude, and oscillation frequency on splitting are quantitatively examined. Stable gradients are also considered. A simple, effective method is proposed for virtually eliminating thermal peak splitting in isothermal capillary GC analysis.
Relation between the programmed and isothermal retention indices in chromatography
Authors: Said A. S. , Jarallah A. M. , Al‐Ameeri R. S. 
Published: May 2005

AbstractA systematic approach was utilized to deduce the relation between the programmed and isothermal retention indices in chromatography. The relation was given in the form of a chart from which the equivalent isothermal temperature Te is plotted vs ΔT′ with IP as the parameter. ΔT′ is a function of both the inlet and outlet temperatures during the temperature programmed run and Te is the temperature at which the isothermal index is equal to the programmed index IP.