Selectivity of stationary phases for the resolution of polycyclic aromatic hydrocarbons

Summary Relative retentions, heats and entropies of solution for 16 PAH in seven different stationary phases were measured under standard isobaric conditions using GC. The experimental conditions to obtain reproducible retention data at non-linear adsorption isotherms are discussed and standard conditions are recommended using the linear relationship between retention time and 1/log h (where h is the peak height). A linear relationship was established between the relative molar heats of solution and the number of carbon atoms in the PAH-molecule. This relationship is valid only for non-polar stationary phases. Certain effects of the isomeric structures of PAH are studied using the relative molar heats and entropies of solution. The latter function is very sensitive to the spherical form of a molecule. Different aspects of isomeric selectivity are discussed and it is concluded that the better way for resolving complex PAH-mixtures is rather an improvement in column efficiency than searching for new stationary phases.     

Propagation of Harmonic Waves in a Cylindrical Shell (Timoshenko Model)

Equations for studying the axisymmetric deformation of a cylindrical shell are derived on the basis of Timoshenko shell theory. A dispersion equation is set up to study natural harmonic waves in a cylindrical isotropic shell. A numerical approach to plotting dispersion diagrams is proposed. The wave velocities obtained coincide with analytical solutions     

Thermal desorption of bromine from a graphite-bromine intercalation compound

Gas chromatography and static adsorption have been used to examine the bromine-graphite acceptor system, which has intercalant structures comparable with the adjacent graphite: layers. The bromine adsorption-desorption isobars and isotherms have been determined at 278–393 K, whose shapes indicate reversible phase transitions between intercalation stages 2 and 4. Measurements at 390–550 K give the desorption activation energies for the two forms of intercalated bromine; the heat involved in the conversion of the ionized intercalant form to the molecular one is 10.4 kJ/mole.Translated from Teoreticheskaya i Ékperimental'naya Khimiya, Vol. 25, No. 1, pp. 120–123, January–February, 1989.