ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Chemistry  (3)
Collection
Keywords
Publisher
Years
  • 1
    ISSN: 1040-7685
    Keywords: gas chromatography ; stationary phases ; poly(siloxanes) ; selectivity ; solvation parameter model ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solvation parameter model is used to characterize the solvent properties of 12 poly(siloxane) stationary phases of varied structure. Selectivity differences are explained in terms of differences in the cohesive energy of the solvents and their capacity for dispersion, dipole-type, hydrogen bonding, and electron pair complexation interactions. None of the poly(siloxane) stationary phases exhibited significant hydrogen-bond acid character. Principal component analysis indicates that replacing a methyl group by a phenyl group in the poly(siloxane) backbone predominantly produces incremental increases in the capacity of the stationary phase for dipole-type interactions (up to about 50 mol% phenyl groups with only small changes at higher phenyl composition). The poly(methylphenylsiloxanes), however, only span a small sector of the selectivity space and provide limited opportunities for selectivity optimization. OV - 275 and QF-1 are identified as important phases with unique characteristics - OV-275 because of its high cohesive energy and great capacity for dipole-type and solvent hydrogen-bond base interactions and QF-1 because of its unusually small hydrogen-bond basicity for a phase with an intermediate capacity for dipole-type interactions as well as a low capacity for n- and π-electron complexation interactions. From these studies it is possible to speculate on the needs for new phases to explore the full selectivity potential of gas chromatography and to address the issue of temperature and its relationship to selectivity. © 1995 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 0935-6304
    Keywords: Solid-phase extraction ; Breakthrough volumes ; Solvation parameter model ; Packing density ; Sorbent characteristics ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetic and retention properties of a silica-based octadecylsiloxane bonded phase sorbent used in solid-phase extraction (SPE) were determined by high pressure liquid chromatography (HPLC). This sorbent had a high bonded phase density resulting in a material with very low intraparticle porosity. This led to favorable retention and mass transfer properties over the normal sampling flow rate range. Typical cartridges for SPE have a low and variable packing density which is recognized as a significant cause of poor sampling performance and, under some circumstances, results in poor repro-ducibility. The apparent particle size for the sorbent at 55-57 μm is considerably larger than generally indicated in the trade literature but this is not detrimental to its use for SPE since sorbent cartridges are able to function adequately with only a few theoretical plates. Solute size is identified as the primary driving force for sorbent retention under SPE conditions with polar interactions favoring retention in the aqueous mobile phase and a decrease in the breakthrough volume. All parameters required to predict the optimum sampling conditions, breakthrough volume and recovery in SPE can be conveniently obtained from data generated by HPLC. The sampling characteristics of particle-loaded membranes are compared to those of conventional sorbent cartridges and differences in operating characteristics which affect the sampling efficiency for both devices are discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 0935-6304
    Keywords: Supercritical fluid extraction ; Series-coupled column gas chromatography ; Chemometric classification ; Semivolatile flavor compounds ; Cinnamon ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvent-assisted supercritical fluid extraction is superior to Soxhlet extraction, solvent extraction at reflux, and simultaneous setam distillation solvent extraction for the isolation of semivolatile compounds from the cinnamons of commerce. Optimized extraction conditions are described using carbon dioxide at 300 atm and 70°C to extract 0.5 g of powdered cinnamon mixed with 4.5 g of anhydrous sodium sulfate to which 1.0 ml of acetonitrile was added at the start of the sequential 30 min static and 30 min dynamic extraction. The semivolatile compounds were collected by solvent trapping in ethyl acetate and analyzed directly by series coupled-column gas chromatography after filtration and partial solvent evaporation. Twenty-one compounds identified by mass spectrometry were quantified in twenty-four samples of cinnamon and cassia purchased in Sri Lanka, Korea, United Kingdom, and the United States of America. True cinnamon is easily distinguished from cassia by the presence of eugenol, absence of δ-cadinene, much lower amounts of coumarin, and larger amounts of benzyl benzoate. Principal component analysis using the relative composition of the twelve major semivolatile compounds provides a clear distinction between true cinnamon and cassia as well as useful interspecies differences which can be used for further classification.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...