Sol-gel stationary phases for capillary electrochromatography

A review is presented on the current state of the art and future trends in the development of sol-gel stationary phases for capillary electrochromatography (CEC). The design and synthesis of stationary phases with prescribed chromatographic and surface charge properties represent challenging tasks in contemporary CEC research. Further developments in CEC as a high-efficiency liquid-phase separation technique will greatly depend on new breakthroughs in the area of stationary phase development. The requirements imposed on CEC stationary phase performance are significantly more demanding compared with those for HPLC. The design of CEC stationary phase must take into consideration the structural characteristics that will provide not only the selective solute/stationary phase interactions leading to chromatographic separations but also the surface charge properties that determine the magnitude and direction of the electroosmotic flow responsible for the mobile phase movement through the CEC column. Therefore, the stationary phase technology in CEC presents a more complex problem than in conventional chromatographic techniques. Different approaches to stationary phase development have been reported in contemporary CEC literature. The sol-gel approach represents a promising direction in this important research. It is applicable to the preparation of CEC stationary phases in different formats: surface coatings, micro/submicro particles, and monolithic beds. Besides, in the sol-gel approach, appropriate sol-gel precursors and other building blocks can be selected to create a stationary phase with desired structural and surface properties. One remarkable advantage of the sol-gel approach is the mild thermal conditions under which the stationary phase synthesis can be carried out (typically at room temperature). It also provides an effective pathway to integrating the advantageous properties of organic and inorganic material systems, and thereby enhancing and fine-tuning chromatographic selectivity of the created hybrid organic-inorganic stationary phases. This review focuses on recent developments in the design, synthesis, characterization, properties, and applications of sol-gel stationary phases in CEC.     

Optimale Bedingungen zur Darstellung von gemischten Chloro-Jodo-Osmaten (IV)

Optimum Conditions for Preparation of Mixed Chloro-Iodo Osmates(IV) Using the rate constants of the substitution reactions in the system [OsCl_nI_6-n]^2-, n = 0–6, the formation of the different mixed-ligand complexes by consecutive reactions can be described quantitatively. From calculated concentration-time diagrams one can take the best conditions for the preparation of the single species. The stereospecific run of the substitution reactions and the formation of pure cis- and trans-complexes are discussed.     

Nuclear quadrupole interaction studies of high pressure phase transitions in InSb

Conclusions This study of the behavior of the EFG in the pressure-induced phase transition in InSb shows a high frequency in the high presure metallic phase, that is compatible with the tetragonal, -Sn like structure, but with a certain degree of imperfection. If this imperfection is in fact some disorder in the In and Sb positions, its amount could be promptly clarified by neutron diffraction, since the similarities of the atomic numbers of In and Sb preclude any easy measurement of superlattice lines by X-ray diffraction techniques.The strong frequency distribution that remains after the reversal of the phase transformation must be related with the peculiar kinetics of this reaction, since it depends on temperature and the time interval and since the same is not observed in the T1 transition. So it seems interesting to study other phase transitions in similar systems. A clarification of the precise nature of the generated defects demands the application of other techniques like transmission electron microsconv and neutron diffraction.If the defects observed here are in fact boundary of domains, it might be possible to relate the domain size with the frequency distribution and then to study, by TDPAC, the kinetics of formation and growth of these domains.Work supported in part by Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq) and Financiadora de Estudos e Projetos (FINEP)     

Hydrogen desorption in Zr3Fe H5.5

Hydrogen desorption during heat treatments of (crystalline) Zr₃FeH_5.5 was studied by Mössbauer spectroscopy (MS), X-ray (powder) diffraction (XRD) and thermal gravimetry (TG). In case of sufficiently slow heating rate all hydrogen effuses below 650°K and no phase segregation occurs. At higher temperatures retained hydrogen induce phase separation into Fe₂Zr (or more likely Fe₂ZrH_x) and zirconium hydride. The existence of a highly disordered f.c. tetragonal ternary hydride phase was also detected both by XRD (a_o=4.76 Å, c=4.96 Å) and MS .     

Tissue characterization of benign brain tumors: use of NMR-tissue parameters

To evaluate the potentials of NMR tissue parameters for tissue characterization we investigated 68 patients with benign brain tumors. Tissue parameters were accurately measured by a recently developed interlaced triple sequence. Each individual tumor was characterized by a set of three numbers (relaxation times T1 and T2 and proton density Rho). Different tumors exhibited significant overlaps of the three tissue parameters. Therefore a reliable prediction of the histological diagnosis based on the quantitative analysis of tissue parameters alone was not possible. T2-prolongation correlated well with water content and "regressive changes" in meningiomas and neuromas.     

Comparison of different methods for calculating the paramagnetic relaxation enhancement of nuclear spins as a function of the magnetic field

The enhancement of the spin-lattice relaxation rate for nuclear spins in a ligand bound to a paramagnetic metal ion [known as the paramagnetic relaxation enhancement (PRE)] arises primarily through the dipole-dipole (DD) interaction between the nuclear spins and the electron spins. In solution, the DD interaction is modulated mostly by reorientation of the nuclear spin-electron spin axis and by electron spin relaxation. Calculations of the PRE are in general complicated, mainly because the electron spin interacts so strongly with the other degrees of freedom that its relaxation cannot be described by second-order perturbation theory or the Redfield theory. Three approaches to resolve this problem exist in the literature: The so-called slow-motion theory, originating from Swedish groups [Benetis et al., Mol. Phys. 48, 329 (1983); Kowalewski et al., Adv. Inorg. Chem. 57, (2005); Larsson et al., J. Chem. Phys. 101, 1116 (1994); T. Nilsson et al., J. Magn. Reson. 154, 269 (2002)] and two different methods based on simulations of the dynamics of electron spin in time domain, developed in Grenoble [Fries and Belorizky, J. Chem. Phys. 126, 204503 (2007); Rast et al., ibid. 115, 7554 (2001)] and Ann Arbor [Abernathy and Sharp, J. Chem. Phys. 106, 9032 (1997); Schaefle and Sharp, ibid. 121, 5387 (2004); Schaefle and Sharp, J. Magn. Reson. 176, 160 (2005)], respectively. In this paper, we report a numerical comparison of the three methods for a large variety of parameter sets, meant to correspond to large and small complexes of gadolinium(III) and of nickel(II). It is found that the agreement between the Swedish and the Grenoble approaches is very good for practically all parameter sets, while the predictions of the Ann Arbor model are similar in a number of the calculations but deviate significantly in others, reflecting in part differences in the treatment of electron spin relaxation. The origins of the discrepancies are discussed briefly.     

Higher-Order Accurate Meshing of Nonsmooth Implicitly Defined Surfaces and Intersection Curves

Computational Mathematics and Mathematical Physics - A higher-order accurate meshing algorithm for nonsmooth surfaces defined via Boolean set operations from smooth surfaces is presented. Input...     

Zur Bestimmung des Stickstoffs in organischen Substanzen

Ohne Zusammenfassung     

Analysis of potassium formate in airport storm water runoff by headspace solid-phase microextraction and gas chromatography–mass spectrometry

Potassium formate was extracted from airport storm water runoff by headspace solid-phase microextraction (HS-SPME) and analyzed by GC–MS. Formate was transformed to formic acid by adding phosphoric acid. Subsequently, formic acid was derivatized to methyl formate by adding methanol. Using sodium [²H]formate (formate-d) as an internal standard, the relative standard deviation of the peak area ratio of formate (m/z 60) and formate-d (m/z 61) was 0.6% at a concentration of 208.5 mg L⁻¹. Calibration was linear in the range of 0.5–208.5 mg L⁻¹. The detection limit calculated considering the blank value was 0.176 mg L⁻¹. The mean concentration of potassium formate in airport storm water runoff collected after surface de-icing operations was 86.9 mg L⁻¹ (n = 11) with concentrations ranging from 15.1 mg L⁻¹ to 228.6 mg L⁻¹.     

Adaptive slit beam shaping for direct laser written waveguides

We demonstrate an improved method for fabricating optical waveguides in bulk materials by means of femtosecond laser writing. We use an LC spatial light modulator (SLM) to shape the beam focus by generating adaptive slit illumination in the pupil of the objective lens. A diffraction grating is applied in a strip across the SLM to simulate a slit, with the first diffracted order mapped onto the pupil plane of the objective lens while the zeroth order is blocked. This technique enables real-time control of the beam-shaping parameters during writing, facilitating the fabrication of more complicated structures than is possible using nonadaptive methods. Waveguides are demonstrated in fused silica with a coupling loss to single-mode fibers in the range of 0.2 to 0.5 dB and propagation loss <0.4 dB/cm.