摘要:

AbstractThe use of per‐O‐alkylated as well as partially alkylated/acylated derivatives of α‐, β‐, and γ‐cyclodextrins as chiral stationary phases has opened many new applications to enantioselective gas chromatography. Chiral recognition is now independent of hydrogen bonding interactions and enantiomer separations are achieved for a large variety of compounds which could not be separated before, including lactones, spiroacetals, alkyl halides, olefins, and even compounds with axi

ISSN:0935-6304    

DOI:10.1002/jhrc.1240121002

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

年代:1989

数据来源: WILEY

摘要:

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 disc

ISSN:0935-6304    

DOI:10.1002/jhrc.1240121003

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

年代:1989

数据来源: WILEY

摘要:

AbstractIdentification and detection limits for scanning and non‐scanning mass spectrometers are discussed. It is theoretically deduced and experimentally confirmed that these limits are on the low pico‐and femtogram levels, respectively, when using conventional secondary electron multiplier‐amplifier systems. The sensitivity can be increased at least tenfold by pulse‐counting techniques, instead of current amplification, provided the chemical noise is sufficiently low. The potential advantages of a detection system for simultaneous ion detection in a significant mass range, for obtaining complete mass spectra in fast GC/MS analyses, are demonstrated. A double focusing mass spectrometer was constructed, using the well‐proven Mattauch‐Herzog principles. By application of an “electronic photoplate”, substance identification in the low femtogram range on a millisecond time scale, so far only accessible for single ion monitoring techniqu

ISSN:0935-6304    

DOI:10.1002/jhrc.1240121004

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

年代:1989

数据来源: WILEY

摘要:

AbstractA method is described for the determination of C10‐C20 hydrocarbons in natural gas. Enrichment by solid phase extraction on ODS followed by liquid desorption was found to give better results than adsorption on Tenax or charcoal followed by liquid or thermal desorptio

ISSN:0935-6304    

DOI:10.1002/jhrc.1240121005

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

年代:1989

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240121006

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

年代:1989

数据来源: WILEY

摘要:

AbstractGlass capillaries coated with four crosslinked and surface‐bonded OH‐terminated polysiloxanes [PS 347.5, OV‐17‐OH, OV‐225‐OH, and OV‐240‐OH] were compared with commonly used methyl‐terminated SP‐2330‐coated columns with respect to their selectivity for the separation of 2,3,7,8‐chloro‐substituted dibenzo‐p‐dioxins and dibenzofurans. The methyl‐ and phenyl‐substituted phases [PS 347.5 and OV‐17‐OH] exhibit only moderate isomer selectivity which limits their applicability in this field. The examined 3‐cyanopropyl‐substituted phases [OV‐225‐OH, OV‐240‐OH, and SP‐2330]allow complete separation of all 2,3,7,8‐chlorosubstituted PCDDs and PCDFs. With SP‐2330 longer columns are required (50 m) for baseline separation of critical groups of isomers. OV‐225‐OH was found to be the most suitable phase as to isomer selectivity. In comparison to SP

ISSN:0935-6304    

DOI:10.1002/jhrc.1240121007

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe reproducibility of peak areas as a function of the technique used for sample injection was investigated in capillary supercritical fluid chromatography (SFC). An injection technique has been developed to increase the volume of sample introduced into the capillary column. Using a modified time‐split injection technique, long injection duration times were successfully applied to achieve lower detection limits. Analytes were effectively focused at the head of the analytical column using a unique pressure trap program. Because this on‐column focusing was performed only by pressure and temperature programming, no instrumental modifications were necessary. Up to 1.0 μL of sample solution was injected onto 50 μm i.d. columns using this technique, with no observable peak splitting. Dual detection using ultraviolet (UV) absorption and flame ionization detection (FID) was performed in series, thereby avoiding the necessity of splitting the column effluent. For the compounds investigated (five nitroaromatics and one phthalate ester), the absolute sensitivity of the UV detector was significantly greater than that of th

ISSN:0935-6304    

DOI:10.1002/jhrc.1240121008

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

年代:1989

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240121009

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

年代:1989

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240121010

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

年代:1989

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240121011

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

年代:1989

数据来源: WILEY