Verbesserungen und Neuconstructionen von Wagen

Ohne Zusammenfassung     

Transient ITP in Nonaqueous CE by Introducing Ions with a Long Hydrophobic Chain as Terminating Ions

Transient isotachophoresis (tITP) is an efficient sample-preconcentration procedure for improving detection limits. An isotachophoretic state exists at the beginning of the procedure as a result of the introduction of both leading and terminating ions into the system. tITP has usually been applied in aqueous media, and hydrophilic compounds have been used as leading and terminating ions; this study, however, focused on nonaqueous capillary electrophoresis (NACE) and use of ions with long hydrophobic chains as terminating ions for tITP. Because the long alkyl or aryl structures of these compounds can lead to low mobility in capillary electrophoresis, use of such ions as terminating ions in tITP can broaden the applicable range of the tITP procedure and achieve the ITP effect under more flexible running conditions.     

An Approach for Microprobe Measurement and Modeling for Millimeter-Wave Application

This paper describes a simple method to check the performance of microprobe. The two-port S-parameters of the microprobe are determined by one-port S-parameters measurement using HP 8510XF Network Analyzer. Based on the measurement, an equivalent circuit model for the microprobe is presented and good agreement between the measurement results and modeling results is obtained.     

Cellular instabilities of expanding hydrogen/propane spherical flames at elevated pressures: theory and experiment

An experimental and theoretical investigation of the onset of cellular instabilities on spherically expanding flames in mixtures of hydrogen and propane in air at elevated pressures was conducted. Critical conditions for the onset of instability were measured and mapped out over a range of pressures and mixture compositions. An asymptotic theory of hydrodynamic and diffusional-thermal cell development on flames in mixtures comprised of two scarce fuels burning in air was also formulated. Predicted values of Peclet number, defined as the flame radius at the onset of instability normalized by the flame thickness, were shown to compare favorably with the experimentally measured values.     

Application of gel-permeation chromatography to studies of the functionality distribution of carboxy- and hydroxy-polybutadienes

Separations of carboxy-polybutadienes and hydroxy-polybutadienes according to functionality have been effected using stepwise elution from silica gel. Recoveries in the 95–100% range have been achieved. Subjection of the fractions obtained from the silica gel separation to analysis via gel-permeation chromatography and infrared or near-infrared spectroscopy yields not only functionality distribution data, but also provides the relationship between molecular weight distribution and functional type. Analytical techniques and interpretation of data are discussed.     

Refinements to the diastereoisomer-specific method for the analysis of hexabromocyclododecane

The emergence of hexabromocyclododecane (HBCD) as a bromine-based flame retardant of concern is partly attributable to recent measurements on the environmental occurrence of the individual diastereoisomers (alpha, beta and gamma). These measurements were fuelled by a newly developed liquid chromatography/tandem mass spectrometric (LC/MS/MS)-based analytical method. However, in the course of our recent studies on the environmental fate and behaviour of the diastereoisomers of HBCD, some interesting features of the LC/MS/MS method became apparent. For example, the ion signal of the native ions was found to be dependent on the final extract volume. This was true for both biotic and sediment samples and was found to arise from the suppression of the ion signal due to endogenous material in the extracts that escape clean-up. We have also found differences in the stability of the diastereoisomers in different solvents. If left unaccounted for, both factors can compromise analytical measurement data. By way of a series of controlled experiments conducted at our two laboratories [Department of Fisheries & Oceans Canada (DFO) and Environment Canada (EC)], we illustrate these features and demonstrate that use of newly synthesized labelled HBCD isomers [(13-carbon (13C) and deuterium (d18)] can minimize and often circumvent matrix-related effects.     

The effect of polyoxyethylene glycol monoethers ofn-hexadecanol on the stability of a polystyrene latex dispersion

The influence of nonionic surface active agents, a series of polyoxyethylene glycol monoethers ofn-hexadecanol, on the stability of dispersions of 2m diameter polystyrene latices has been investigated.Adsorption and microelectrophoretic studies showed the presence of looped monolayers of surface active agent at plateau adsorption.Examination of sedimentation volumes and redispersibility, correlated with potential energy calculations, showed that the stability of the dispersions depended on the characteristics of the adsorbed layer and on added electrolyte.     

The molecular potential energy surface and vibrational energy levels of methyl fluoride. Part II

New analytical bending and stretching, ground electronic state, potential energy surfaces for CH(3)F are reported. The surfaces are expressed in bond-length, bond-angle internal coordinates. The four-dimensional stretching surface is an accurate, least squares fit to over 2000 symmetrically unique ab initio points calculated at the CCSD(T) level. Similarly, the five-dimensional bending surface is a fit to over 1200 symmetrically unique ab initio points. This is an important first stage towards a full nine-dimensional potential energy surface for the prototype CH(3)F molecule. Using these surfaces, highly excited stretching and (separately) bending vibrational energy levels of CH(3)F are calculated variationally using a finite basis representation method. The method uses the exact vibrational kinetic energy operator derived for XY(3)Z systems by Manson and Law (preceding paper, Part I, Phys. Chem. Chem. Phys., 2006, 8, DOI: 10.1039/b603106d). We use the full C(3v) symmetry and the computer codes are designed to use an arbitrary potential energy function. Ultimately, these results will be used to design a compact basis for fully coupled stretch-bend calculations of the vibrational energy levels of the CH(3)F system.