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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 50 (1990), S. 39-42 
    ISSN: 1432-0630
    Keywords: 78.70.D ; 81.90.+c
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Positron lifetime spectra were re-measured for a series of synthetic zeolites using a large time window of observation. Magnetic quenching experiments were also performed for the zeolites, and it has been confirmed that both the λ4 and the λ3 components are due to o-Ps. The annihilation rate of the third component, λ3, showed a good correlation with the size of the largest voids, which is similar to the correlation reported for other compounds. However the annihilation rate of the longest-lived component, λ4, showed a poor correlation with the void size. The λ3 component has thus been assigned to o-Ps in the regular voids of the zeolites, and the λ4 component to that escaped to inter-particle open spaces.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Hydrophobic parameter ; Capacity factor variation ; Organic modifier concentration ; Displacement model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The dependence of the capacity factor (k′) on the concentration of the organic modifier (D) in the aqueous binary mobile phase in reversed-phase high-performance liquid chromatography has been investigated to evaluate the hydrophobicity of the solute molecule. The r-values, defined as the slope of log k′ vs. log(1/D) plots, were measured for various solutes and related to the non-polar surface area and the partition coefficients. The r-value was found to be a good indication of solute hydrophobicity. Detailed investigation of the results allowed to consider statistically the molecular posture of the solute adsorbed onto the stationary alkyl ligand.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Reversed stationary phases ; Hydrophobic parameter ; Water/methanol eluent mixtures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The hydrophobic retention characteristics of stationary ligands for reversed-phase high-performance liquid chromatography have been evaluated from the slope (r-value) of the plots relating the capacity factors (log k′) of selected aliphatic and aromatic compounds with the reciprocal of methanol concentration (log (1/[MeOH])) in aqueous mobile phase. Octadecylsilyl (ODS), trimethylsilyl (TMS) and phenyldimethylsilyl (phenyl) groups were selected as the stationary ligands bonded to silica support. On ODS or TMS silicas, unlike on phenyl silica, aliphatic compounds gave slightly larger r-values than aromatic compounds, indicating that the shape of the ligand recognizes the hydrophobic surfaces of aliphatic and aromatic solute molecules. On TMS and phenyl silicas, the degree of solute hydrophobicity contributing to its retention is about 90% and 85% of that on ODS silica, respectively. On the other hand, on TMS and phenyl silicas, the polar functional group on the solute molecule brought about a smaller decrease in retention than on ODS silica.
    Type of Medium: Electronic Resource
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