Arsen

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Radioaktive Untersuchungen

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Unusual features of micellar diffusion

Diffusion coefficients of tetradecyltrimethylammonium bromide in aqueous solutions have been determined at 25, 95 and 135 °C using the Taylor dispersion technique. The diffusion coefficient exhibits a minimum at a surfactant concentration above the critical micelle concentration (CMC). The results are interpreted in terms of electrostatic coupling and rapid exchange between micelle, surfactant monomer and counterions.     

Mass spectrometric behavior of levoglucosan under different ionization conditions and implications for studies of cellulose pyrolysis

Pyrolysis-mass spectrometric studies of cellulose indicate low abundances of levoglucosan in the product spectrum compared to the yield values determined in more conventional types of pyrolysis studies. To examine the reason for these conflicting observation, levoglucosan was examined under different ion source conditions and ionization modes to ascertain the relative contributions of thermal degradation and ionization fragmention to the low abundances of the levoglucosan molecular ion. Low-energy electron ionization using conventional sample volatilization and molecular-beam sampling is compared to chemical ionization using methane, isobutane, and ammonia as reagent gases, and to field ionization and desorption. The mass spectrometric fragmentation patterns under the various systems indicate that studies of cellulose pyrolysis underestimate the amount of levoglucosan formed due to ionization fragmentation and thermal rearrangement reactions in the ion source. Several peaks, including m/z 126 and 144, are dominated by the contribution from the fragmentation of levoglucosan.     

A study of the oxidation of vegetable oils by inverse gas chromatography

Summary Inverse gas chromatography is shown to be suitable for the study of the oxidation of vegetable oils. With air as carrier gas characteristic plots of retention index versus time are obtained for hydroxylic test solutes that are consistent with the oxidation behaviour of vegetable oils. Shifts of retention are found to be accompanied by changes of column efficiency due to the oxidative crosslinking of polyunsaturated vegetable oils. The technique also leads to useful information concerning the oxidation of antioxidant inhibited systems. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Critical micelle concentrations for alkyltrimethylammonium bromides in water from 25 to 160°C

Critical micelle concentrations were determined by conductance measurements for decyl-, dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromide in water at 25, 60, 95, 130, and 160°C. The results are discussed in terms of the equilibrium model and the nonlinear Poisson-Boltzmann model for micelle formation. The free energies of transferring a methylene group from water to the oil-like interior of the micelle are found to be –781 at 25°C, –796 at 60°C, –819 at 95°C, –815 at 130°C, and –787 at 160°C cal-mol^–1.