Muon spin relaxation in heavy fermion systems

Heavy fermion systems have received a great deal of study by a wide variety of techniques, includingSR. In a number of systems, coexisting superconducting and magnetic states have been reported, leading to speculation of an intimate connection between magnetism and superconductivity in these compounds. We observe a spontaneous magnetic field in the superconducting phase of UPt₃. In addition, the broadening of the transverse field muon precession signal only onsets approximately 60 mK below the superconductingT _c. Our results provide evidence that the lower superconducting phase in theH-T phase diagram of UPt₃ is characterised by broken time-reversal symmetry. Measurements of URu₂Si₂ and CeCu_2.2Si₂ indicate that the magnetically ordered volume fraction is temperature dependent in both systems.     

Fast analysis of flavonoids in plant extracts by liquid chromatography-ultraviolet absorbance detection on poly(carboxylic acid)-coated silica and electrospray ionization tandem mass spectrometric detection

A highly hydrophilic poly(7-oxonorbornene-5,6-dicarboxylic acid-block-norbornene) [=poly-(ONDCA-b-NBE)]-coated silica was investigated for the liquid chromatographic (LC) determination of flavonoids in plant extracts of complex biological origin using UV absorbance and mass spectrometric (MS) detection. Compared to the most commonly used octadecyl derivatized silica this sorbent allowed fast separations even at extreme pH values. Furthermore, UV absorbance and MS detection were evaluated. As we found, UV detection at 254 nm allows the determination of flavonoids down to the ng range with a linearity of R2>0.9906. For the more selective characterization the validated LC system was coupled to a quadrupole ion trap mass spectrometer via an electrospray ionization (ESI) interface. MS detection showed high linearity (R2>0.9904) for all investigated flavonoids. Due to the relatively high flow-rate of 1 ml/min the limits of detection were found in the lower-microg range. Collision induced dissociation was applied to obtain characteristic fragmentation fingerprints. Finally, the validated LC-ESI-MS-MS method demonstrated that this poly-(ONDCA-b-NBE) stationary phase allows fast characterization and quantitation in onion, elderflower blossom, lime blossom, St. John's Wort and red wine.     

Adsorption and dissociation of NO on stepped Pt (533)

We present an experimental and theoretical investigation of the adsorption, desorption, and dissociation of NO on the stepped Pt (533) surface. By combining temperature programmed desorption and reflection absorption infrared spectroscopy, information about the adsorption sites at different temperatures is obtained. Surprisingly, metastable adsorption structures of NO can be produced through variation of the dosing temperature. We also show that part of the NO molecules adsorbed on the step sites dissociates around 450 K. After dissociation the N atoms can desorb either by combining with an O fragment, or with another N atom, resulting in NO and N(2). The N(2) production can be enhanced by coadsorbing CO on the surface: CO scavenges the oxygen atom, thereby suppressing associative recombinative desorption of N and O atoms. Density functional theory calculations are used to reveal the adsorption energies and vibrational frequencies of adsorbed NO as well as barriers for dissociation of NO and for diffusion of N atoms. The combined experimental results and theoretical calculations reveal that dissociation of NO is the rate limiting step in the formation of N(2).     

Metal ion capillary zone electrophoresis with direct UV detection: Comparison of different migration modes for negatively charged chelates

Summary Several migration modes suitable for capillary zone electrophoretic (CZE) separation of metal ions in the form of 8-hydroxyquinoline-5-sulphonic acid complexes are described and compared. Superior analysis time, resolution, efficiency and detectability were achieved using reversed movement of anionic metal complexes (in the anode-to-cathode direction) under the action of the electroosmotic flow. This method allows the CZE analysis of multicomponent mixtures of transition metal ions as well as aluminium within about six minutes.     

Capillary zone electrophoretic analysis of carbohydrates by direct and indirect UV detection

Summary The analysis of carbohydrates has been always hampered by their lack of UV absorbance above 200 nm, which is an especially challenging problem in capillary electrophoresis due to the very small (nl) sample volumes injected. The introduction of 2-aminopyridine as derivatizing agent allows sensitive direct UV detection of saccharides in the fmol range. However, due to the requirement of the presence of a free aldehyde group only aldoses and uronic acids can be determined. This limitation was recently overcome by means of precolumn derivatization withp-aminobenzoic acid or ethylp-aminobenzoate, which permits the analysis of fructose with a lower mass detection limit of 0.3 and 0.14 pmol, respectively. The detection limits for aldoses were even as low as 15 and 7 fmol. A more universal approach is the use of indirect UV detection, which permits the analysis of carbohydrates, including (1–2)-linked disaccharides and aldonic acids, at the lower pmol level without the need for derivatization.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.