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  • 1
    ISSN: 1612-1112
    Keywords: Gas-liquid chromatography ; Thermodynamic models ; Solvent selectivity ; Multivariate analysis ; Stationary phases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Rapid progress has been made in the last few years in the development of solvation models for gas chromatography. These models are based on the free energy of transfer of a solute from the gas phase to solution consisting of the additive processes of cavity formation and solute-solvent interactions expressed as dispersion, orientation, induction and hydrogen-bond formation. The adaptation of these models to characterize solvent selectivity for a wide range of common stationary phases and to the prediction of retention is critically discussed. The need to use high quality retention data in the further elaboration of solvation models is also demonstrated.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 39 (1994), S. 200-209 
    ISSN: 1612-1112
    Keywords: Multidimensional gas chromatography ; Arson investigation ; Petroleum distillates ; Target compound identification ; Headspace sampling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method for identifying petroleum distillates (accelerants) in fire debris samples by dynamic headspace analysis and multidimensional gas chromatography is described. The method relies on the separation of target compounds characteristic of different petroleum distillate classes from interfering co-eluting and matrix components. A relatively nonpolar column is used to characterize the volatility distribution of the sample and heartcutting to a second polar column of certain fractions to separate target compounds from interferences unresolved on the first column. The method is demonstrated for the identification of gasoline, kerosene, charcoal lighter fluid, and paint thinners in simulated arson samples.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Semivolatile flavor compounds ; Cinnamon ; Solid-phase microextraction ; Chemometric classification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The conditions which affect the reproducibility of characteristic chromatographic profiles of semivolatile compounds from true cinnamon and cassia by headspace solid-phase microextraction are determined. Optimum conditions for sample amount, vial size, temperature, sampling time, and fiber type for steady state sampling conditions are identified. Vial size was an unexpected critical parameter possibly related to the build up of internal ternal pressure during sample heating followed by expulsion of a portion of the vapor phase through the septum as it was punctured by the syringe. Gas chromatography with ion trap mass spectrometry was used to identify the major volatile compounds in cassia and true cinnamon. Reasonable semi-quantitative agreement (r 2〉0.87 and generally greater than 0.93) was observed for the major semivolatile compounds isolated by headspace solid-phase microextraction and solvent-assisted supercritical fluid extraction. The extracts isolated by solid-phase microextraction contained relatively high concentrations of terpene-type compounds in low abundance in the solvent-assisted supercritical fluid extracts, but these compounds were of little value in distinguishing the botanical origin of authentic cinnamon and cassia samples. The latter were easily distinguished by the presence of eugenol and benzyl benzoate in true cinnamon, that was absent in cassia, and the presence of coumarin and δ-cadinene, in cassia, that was either absent or in low concentration in true cinnamon. Headspace solid-phase microextraction provides a rapid and simple method for establishing the botanical origin of the principal cinnamons of commerce.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 66 (1979), S. 423-424 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ternary mobile phase compositions ; Solvation parameter model ; Mixture-design optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new approach is presented fro the prediction of retention in reversed-phase liquid chromatography using ternary mobile phase compositions. The solvation parameter model is used to create the system constants that characterize the properties of the mobile and stationary phases in terms of the relative ease of cavity formation, and differences in dispersion, lone pair electron, dipole-type, and hydrogen-bond association interactions for all solvent compasitions employed. A statistical mixture-design approach provides system surfaces and models for the variation of individual system constants as a function of ternary solvent composition. The models for the system surfaces allow the retention factor to be predicted as a function of mobile phase composition for any compound whose descriptor values are known, or can be obtained from estimation rules or determined by experiment. The method is validated using a large literature data base for the retention factor of up to 46 varied aromatic solutes in 72 methonolacetonitrile-water and methonol-tetrahydrofuran-water mobile phase compositions.
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  • 6
    ISSN: 1612-1112
    Keywords: Thin layer chromatography ; Automated multiple development ; Vanilla flavors ; Food analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Thin layer chromatography on silica gel high performance layers and automated multiple development was used to separate the polar aromatic flavor compounds vanillin, ethyl vanillin, 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 4-hydroxybenzyl alcohol, vanillic acid, coumarin, piperonal, anisic acid, and anisaldehyde commonly found in extracts of natural and artificial vanilla flavors. The ratio of 4-hydroxybenzoic acid, 4-hydroxybenzaldehyde and vanillic acid to vanillin in natural vanilla extracts was used to confirm the authenticity of extracts purchased in the United States of America and the United Kingdom. Natural vanilla extracts purchased in Mexico and Puerto Rico were identified as counterfeit products based on changes in the above ratio and the presence of synthetic flavor compounds such as ethyl vanillin and coumarin. It is also demonstrated that the proposed method is suitable for the determination of natural and synthetic vanilla flavors in solvent extracts from food, beverage and confectionery products. The main advantage of thin layer chromatography for the analysis of vanilla extracts and food stuffs flavored with vanilla is its high sample throughput since sample preparation requirements are minimal and multiple samples can be separated simultaneously.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid-phase extraction ; Solvent effects ; Solvation parameter model ; Cyanopropylsiloxane-bonded, silica-based sorbent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The solvation parameter model is used to characterize the retention properties of a cyanopropylsiloxane-bonded, silica-based sorbent with methanol, acetonitrile, tetrahydrofuran, and isopropanol in water as mobile phases. The system constants over the composition range 1 to 50% (v/v) organic solvent indicate that retention occurs because of the relative ease of cavity formation in the solvated stationary phase compared to the same process in the predominantly aqueous mobile phase as well as from more favorable stationary phase interactions with solutes containing π- and n-electrons. The capacity of the solute for dipole-type interactions is not important whereas all hydrogen-bond-type interactions result in reduced retention. Graphing the system constants as a function of mobile phase composition provides a simple mechanism for interpreting the change in capacity of the chromatographic system for retention in terms of changes in the relative weighting of fundamental intermolecular interactions. A comparison is also made with the retention properties of an octadecylsiloxane-bonded, silica-based sorbent with 30% (v/v) methanol in water as the mobile phase and the extraction characteristics of a porous polymer sorbent with 1% (v/v) methanol, acetonitrile, tetrahydrofuran, and isopropanol in water as the sample processing solvent. Changes in sorbent selectivity due to selective uptake of the processing solvent are much smaller for the cyanopropylsiloxane-bonded sorbent than the results found for a porous polymer sorbent.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1612-1112
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 3,5-dichlorobenzeneboronic acid and 3-nitrobenzeneboronic acid have been evaluated as selective reagents for the derivatization of proximinal bifunctional compounds. Their gas chromatographic properties and response to the electron-capture detector are described.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 17 (1983), S. 370-374 
    ISSN: 1612-1112
    Keywords: Organic Molten Salt ; 1-Ethylpyridinium Bromide ; Stationary Phase Properties ; Gas Chromatography ; McReynolds constants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The organic molten salt, 1-ethylpyridinium bromide, is suitable for use as a stationary phase in gas chromatography. It has a usable liquid temperature range of 110 to 160°C. It undergoes a single phase transition at 110°C which corresponds to the bulk melting point. Below the melting point the phase may be used as a selective adsorbent, although column efficiency and peak symmetry deteriorate as the temperature is lowered from the melting point. Above the melting point, ethylpyridinium bromide can be used to separate a wide variety of organic compounds retaining strongly those compounds possessing large dipole or hydrogen bonding functional groups.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 18 (1984), S. 234-238 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Open-tubular columns ; On-column injection ; Stopped-flow operation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple, inexpensive, on-column injector of the septum moving-needle kind is described for quantitative analysis using open-tubular columsn. when operated in the stopped-flow mode an improvement incolumn efficiency is observed combined wit a diminished tendency to produce split-top peaks, particularly for late eluting peaks. Using electronic integration a relative error of about 2.7% was observed for peaks spanning a wide range of sample concentrations and volatilities.
    Type of Medium: Electronic Resource
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