Improved quantification limits in chiral capillary electrochromatography by peak compression effects

The peak compression effect has been applied to improve quantification limits in chiral capillary electrochromatography (CEC). A stationary phase based on the chiral selector vancomycin (Chirobiotic V) was used for separations of the enantiomers of mianserin. By adding solvents with a low dielectric constant, e.g. 2-propanol or tetrahydrofuran, to the sample solution, peak compression could be induced. The plate numbers for the minor enantiomer increased from approximately 100,000 to 1.4-1.6 million plates/m, when the composition of the mobile phase was adjusted so that the analyte eluted within either one of two system zones originating from the sample solution. A 10-fold improvement in the quantification limit for the minor enantiomer was obtained compared to elution under non-focused conditions.     

Determination of average degree of polymerisation and distribution of oligosaccharides in a partially acid-hydrolysed homopolysaccharide: a comparison of four experimental methods applied to mannuronan

The average degree of polymerisation (DP) and distribution of oligosaccharides in partially acid hydrolysed mannuronans were quantitatively evaluated by 1H NMR, electrospray ionisation mass spectrometry (ESI-MS), micellar electrokinetic capillary chromatography with UV detection (MEKC-UV), and high-pressure anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Our investigation shows that 1H NMR, MEKC-UV and, in particular, HPAEC-PAD can be used as quantitative tools to aid the investigation of polysaccharide structure, function and synthesis. For the latter two techniques, especially, this represents a significant new development as it enables calculation of the quantity of individual oligomers of nominal DP by direct analysis of a defined oligomer mixture. Appropriate statistical averages of number and weight distributions were also calculated and found to fit very well to predicted Kuhn distributions that assume random depolymerisation.     

Criteria for local equilibrium in a system with transport of heat and mass

Nonequilibrium molecular dynamics is used to compute the coupled heat and mass transport in a binary isotope mixture of particles interacting with a Lennard-Jones/spline potential. Two different stationary states are studied, one with a fixed internal energy flux and zero mass flux, and the other with a fixed diffusive mass flux and zero temperature gradient. Computations are made for one overall temperature,T=2, and three overall number densities,n=0.1, 0.2, and 0.4. (All numerical values are given in reduced, Lennard-Jones units unless otherwise stated.) Temperature gradients are up to T=0.09 and weight-fraction gradients up to w ₁=0.007. The flux-force relationships are found to be linear over the entire range. All four transport coefficients (theL-matrix) are determined and the Onsager reciprocal relationship for the off-diagonal coefficients is verified. Four different criteria are used to analyze the concept of local equilibrium in the nonequilibrium system. The local temperature fluctuation is found to be T0.03T and of the same order as the maximum temperature difference across the control volume, except near the cold boundary. A comparison of the local potential energy, enthalpy, and pressure with the corresponding equilibrium values at the same temperature, density, and composition also verifies that local equilibrium is established, except near the boundaries of the system. The velocity contribution to the BoltzmannH-function agrees with its Maxwellian (equilibrium) value within 1%, except near the boundaries, where the deviation is up to 4%. Our results do not support the Eyring-type transport theory involving jumps across energy barriers; we find that its estimates for the heat and mass fluxes are wrong by at least one order of magnitude.     

Development of a very low energy μ+ beam at PSI

At PSI we are investigating the technique of decelerating an existing very intense secondary beam of surface ⁺ (4 MeV) to an energy of 10 eV using appropriate moderators. These ⁺ can then be used as a source of a tertiary beam of low energy muons with tunable kinetic energy between 10 eV and 10 keV.With a 1000 A layer of solid Argon deposited on an Al substrate we obtain a moderation efficiency (with respect to the number of incoming surface ⁺) of the order of 10^–4.Results of our investigations and the present status of the project are presented together with future plans and possibilities.     

At-column injector for capillary GC — design and evaluation

The present paper describes constructional details and evaluations of an at-column injector for capillary GC. Injections were made via a sample loop on a 0.32 mm i.d. capillary column. Two rotary valves were employed to allow a wash of the sample loop and a backflush of the transfer line. Repeatability, calculated from absolute area counts for n-alkanes was between 0.3–1% RSD, for injected sample volumes between 5 and 100 μl. Promising results were also obtained with syringe-based injections on narrow bore (100 μ i.d.) columns. Repeatability on the basis of normalized area counts was in the order of 0.1–0.2% RSD, while solvent tailing was practically absent.     

Structure and dynamics of self-assembled poly(ethylene glycol) based coiled-coil nano-objects.

Herein we describe the structure and dynamics of self-assembled nano-objects generated from poly(ethylene glycol) based (PEG-ylated) coiled-coil hybrid block copolymers. Electron paramagnetic resonance (EPR) experiments on spin-labeled samples provided a strong indication for a parallel alignment of the peptide helices in at least the dimeric coiled-coil nano-object and indicated that the PEG chains are folded rather closely around the peptide core of the nano-objects. The EPR results were supported by AFM studies, which revealed the presence of discrete nanosized objects in thin, spin cast films of the block copolymers on mica substrates. Since their size and structure may be engineered via directed mutations in the amino acid sequence, these nano-objects may be interesting building blocks for the development of supramolecular materials with various potential applications.