High-performance anion-exchange chromatography of carbohydrates using a new resin and pulsed amperometric detection

Summary This paper reports the results of a study on the use of a new polymer-based, strong anion-exchange, stationary phase for rapid and selective separation of carbohydrates and related compounds by high-pH, anion-exchange chromatography with pulsed amperometric detection. The new adsorbent has been obtained by direct nitration of 2.8 μm, spherical non-porous highly cross-linked, styrene-divinylbenzene copolymer beads, followed by reduction of superficially introduced nitro groups with nascent hydrogen and quaternization of the resultant amino groups with iodomethane. It is reported that by optimizing the ionic strength of the mobile phase, columns packed with the new anion-exchanger can be successfully employed to separate, either in isocratic or gradient elution mode, oligosaccharides, positional isomers of gluco-disaccharides, as well as uronic acids and sugar monophosphates.     

Indirect UV detection of carbohydrates in capillary zone electrophoresis

Summary A new system for the rapid and sensitive analysis of underivatized carbohydrates has been established using capillary zone electrophoresis with indirect UV detection. At an applied potential of 28 kV, sugars and sugar acids could be separated by the combined effects of electroendosmosis and electrophoresis within 20 minutes in a fused silica capillary of 50 m internal diameter and an effective length of 100 cm using 6mM sorbic acid, pH 12.1, as both carrier electrolytie and chromophore. The alkaline pH ensured ionization of the sugars and, hence, their detection by means of charge displacement. Furthermore, the chosen concentration of sorbic acid allowed the smallest fractional change in the background signal to be measured. While the electrophoretic mobilities of the sugars were found to increase within a pH range of 11.9 to 12.3, those of the sugar acids were not affected. Due to the increasing competition of hydroxide ions in the displacement of the chromophore with rising pH, a significant loss of sensitivity is observed at pH values higher than 12.1 and this pH was found to provide sufficient resolution, optimum sensitivity, and a acceptably short analysis time. Under these conditions, a lower detection limit of 2 pmol was obtained for glucose.     

Theory of bulk, surface and interface phase transition kinetics in thin films

We report a theoretical study of phase transition kinetics in confined two-dimensional systems, motivated by recent experimental results on the amorphous-to-crystalline transition in supported, thin amorphous water films [E.H.G. Backus, M.L. Grecea, A.W. Kleyn, and M. Bonn, Phys. Rev. Lett. (to be published)]. We generalize and extend existing theories to simultaneously describe the converted (crystalline) fractions in the bulk, at the sample-vacuum surface, and at the sample-support interface as a function of time. The general approach presented here results in expressions for the time-dependent converted bulk, surface, and interface fractions, for arbitrary desorption rate from the thin film, nucleation and growth rates and also includes finite nucleation grain size. The converted bulk, surface, and interface fractions are calculated for nucleation of the new phase occurring (i) in the bulk, (ii) at the support-sample interface, and (iii) at the sample surface (sample-vacuum interface), resulting in nine expressions. The results demonstrate the advantage of monitoring bulk, surface and interface fractions simultaneously to make definite statements regarding the location of the nucleation, and to reliably determine the values of the relevant crystallization parameters.     

Metal ion capillary zone electrophoresis with direct UV detection: determination of transition metals using an 8-hydroxyquinoline- 5-sulphonic acid chelating system

The application of capillary zone electrophoresis to the separation and determination of metal ions after the precolumn formation of negatively charged chelates is described. Multi-component mixtures of transition metal complexes with 8-hydroxyquinoline-5-sulphonic acid (HQS) were separated in about 10 min in a fused-silica capillary column with a borate buffer of pH 9.2 at an applied voltage of 15 kV followed by direct UV detection. The capillary pretreatment with an electroosmotic flow modifier, namely a tetraalkylammonium salt, is necessary to achieve resonable migration times of these metal complexes. Incorporating the chelating reagent in the electrophoretic buffer markedly improves the detectability of relatively unstable chelates, such as those of Co(II), Zn(II) and Cd(II), and allows the separation of metal ions that form unstable HQS chelates, such as Mn(II) and alkaline earth metals. The effects of electrophoretic buffer parameters affecting the complexation reaction and migration behaviour are discussed. Linearity of calibration graphs is observed for about three orders of magnitude with sub-ppm detection limits. The applicability of the method to the analysis of real samples is demonstrated.     

Temperature dependence of the magnetic penetration depth in YBa2Cu3O6.95

We report precision transverse fieldSR measurements of the internal field distribution in the vortex state of crystalline YBa₂Cu₃O_6.95. A novel low background apparatus was used to study a mosaic sample of three high quality single crystals (T_c=93.3K). The observed frequency spectra in magnetic fields of 5kG and 15 kG applied along the c-axis have the characteristic features expected for a regular vortex lattice with some additional broadening. From a preliminary analysis we find that [(0)/(T)]² has a linear temperature coefficient forT<30 K. Such a term is inconsistent with simple s-wave pairing in the superconducting state. These results support recent microwave measurements of(T) on similar crystals in zero applied field but differ significantly from previousSR reports on sintered powders and crystals with lower T_c.This research was supported by the Natural Sciences and Engineering Research Council of Canada.