摘要:

AbstractAlthough the classical retention theory is used for interpreting data or optimizing separations in sedimentation field‐flow fractionation (SedFFF), as in most other field‐flow fractionation techniques, the assumption of a parabolic flow profile on which this theory is based is not rigorously correct in SedFFF because of the curvature of the channel walls. In order to examine quantitatively the influence of this effect, the relative velocity profile in SedFFF is obtained by solving the Navier‐Stokes equation in cylindrical coordinates. Discrepancies found in the literature about the definition of the mean velocity in such channels are discussed. Relationships between mean velocity, flow‐rate and pressure gradient are given.Approximating the velocity profile by a third‐degree polynomial of the radial coordinate which provides the same slope as the exact profile at a reference wall, for small values of δ, the curvature ratio (ratio of the channel thickness to the mean curvature radius), shows that the adjustable parameter of the approximate profile, ν, is equal to ± δ/3, the sign depending on whether the reference wall is the inner or outer wall. The curvature ratio appears to be a good indicator of the error made on retention when using the straight channel approximation in retention theory. The error is quite small for typical SedFFF channels. It may have to be taken into account for precise determinations if thicker channels and/or miniaturized sys

ISSN:0935-6304    

DOI:10.1002/jhrc.1240190902

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractGas chromatrography (GC) with sulfur chemiluminescence detection (SCD) is an outstanding combination for selectively determining trace concentrations of sulfur compounds in hydrocarbon samples. GC peaks can be identified by retention times when reproducible, automated injection techniques are used. However, as described in this work, analysts should be on the look out for retention shifting due to solvent effects from sample components. Three examples of retention shifting are presented: (1) thiophene by benzene; (2) methylthiophenes by toluene; and (3) dibenzothiophene by gas oil. Depending on samples and analysis conditions, retention shifts from a few hundredths to 1.5 min have been observed. Such retention shifts are likely to cause errors in peak identifications. Therefore, when using SCD, simultaneous FID monitoring is recommended as an aid in evaluating chromatograms for possible retention shifting due to solvent effects.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240190903

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractTen different metal tubings were investigated for thermal decomposition of analytes when used as the trap tube in a cryotrap/thermodesorption inlet system. No noticeable sample decomposition of hydrocarbons, chlorinated hydrocarbons and a brominated hydrocarbon was observed for six of the tubings with hydrogen as the carrier gas. This observation may be partly attributed to the developed deactivation techniques that produce inert metal tubings that are being widely adopted by many column manufacturers, the different trap materials used in comparison to previous studies and the decreased sample residence time in the hot trap tube. A cryotrap using carbon dioxide was constructed and tested as a alternative to the previously used liquid nitrogen based systems. This cryotrap was able to trap compounds with a boiling point of 80°C

ISSN:0935-6304    

DOI:10.1002/jhrc.1240190904

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractThe seed oils of three Maytenus species have been examined by high temperature GLC using SOP‐50 (methoxy‐terminated) and OV‐225‐OH (OH‐terminated) glasscapillary columns. The main compounds (71–76%) could be identified as α‐mono‐acetotriacylglycerols by a combination of high temperature GLC‐MS in negative chemical ionization mode with a CH4/N2O mixture as reactant gas and other spectroscopical methods (infrared,1H‐ and13C‐nuclear magnetic resonance spectroscopy). The OV‐225‐OH phase demonstrated better separation properties that the SOP‐50 phase for this substance class and up to eight species of α‐monoacetotriacylglycerols could be separated. The content of usual triacyclglycerols was below 1%. The results of the analysis of the individual fatty acids as their methyl esters by

ISSN:0935-6304    

DOI:10.1002/jhrc.1240190905

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractOne of the most widely acclaimed features of capillary and microcolumn LC, in comparison with conventional HPLC, is the enormous increase in mass sensitivity. Nevertheless, application of capillary and micro LC in quantitative trace bioanalysis, characterized by weak analyte concentrations in complex matrices, can only be of any practical utility if large sample volumes can be injected onto the columns without affecting chromatographic resolution and efficiency.Two applications of large volume injection in a non‐eluting solvent (on‐column focusing) for the quantitative analysis of drugs in biological fluids on both capillary and micro chromatographic systems are presented: the first example deals with a new selective H1‐antihistaminic drug, mizolastine, the second one with a well known calcium antagonist, diltiazem, and its main metabolites. For both compounds, results obtained on micro and capillary LC in comparison with conventional HPLC are reported. The results demonstrate that when conventional HPLC methods are transformed into either micro or capillary LC techniques, they gain in sensitivity. By means of an on‐column focusing technique, it is possible to increase the sensitivity 3–5 fold in comparison to conventional HPLC methods, but not 50–60 fold as obtained on synthetic drug solutions. Column robustness, handiness, reproducibility, and suitability of micro systems for routine bioanalysis are discussed for both capillary and micro LC columns, as well as limits of the technique in trace organic analys

ISSN:0935-6304    

DOI:10.1002/jhrc.1240190906

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractThe enantiomers of amino acids were first converted intoN‐alkyloxycarbonyl 2,2,2‐trifluoroethyl esters, and then intoN‐alkyloxycarbonyl alkylamides by nucleophilic substitution of the ester group with amines. The first reaction proceeds instantaneously, while the second substitution occurs smoothly withn‐propylamine and isobutylamine. The final derivatives were produced for separation on a capillary column coated with Chirasil‐Val by GC. Pro, which is difficult to separate completely as itsN‐perfluoroacyl alkyl ester derivative, showed complete separation of the enantiomeric pair. All amino acids examined in this study showed an increased separa

ISSN:0935-6304    

DOI:10.1002/jhrc.1240190907

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractSolid phase microextraction (SPME) was applied in the development of a protocol for the analysis of a number of target organic compounds in landfill site samples. The selected analytes, including aromatic hydrocarbons, chlorinated hydrocarbous, and unsaturated compounds, were absorbed directly from a headspace sample above a soil layer onto a fused silica fiber. Following exposure, the fiber was thermally desorbed in the injection port of the gas chromatograph and eluted compounds were detected using a mass selective detector. The stability and sensitivity of the extraction technique were examined at five temperatures (22–60°C) using a 100μm polydimethylsiloxane fiber. Calibrations, using soil samples spiked with selected solvents (0.5–30 μg/g), were linear; trichloroethene (r2= 0.992) and benzene (r2= 0.998). SPME was applied to the examination of a municipal landfill where 8 sites were sampled, at three depths, resulting in the detection of xylene (maximum 2.8 μg/g) and a number of other non‐target organic con

ISSN:0935-6304    

DOI:10.1002/jhrc.1240190908

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240190909

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240190910

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240190911

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY