Zero‐dead‐volume interfaces for two–dimensional electrophoretic separations

We present the study on the sample transfer characteristics of two different microfluidic interfaces for 2D‐CE . These interfaces were manufactured using two different microfabrication technologies: one was obtained via the classical photolithography—wet etching—anodic‐bonding process; and the other was obtained via the selective laser‐induced etching process. The comparison of the two interfaces, and an intact capillary as a reference, was made via the CE separation of amino acids (arginine and lysine) under different bulk flow conditions, with and without applying bias potential to the secondary channels. The influence on peak shapes, migration times, and repeatabiliy were evaluated.     

Capillary electrophoresis-laser induced fluorescence-electrospray ionization-mass spectrometry: a case study

The simultaneous hyphenation of capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection and electrospray ionization-mass spectrometry (ESI-MS) as a novel combined detection system for CE is presented. beta-Carbolines were chosen as model analytes with a forensic background. Nonaqueous CE as well as conventional CE with an aqueous buffer system are compared concerning efficiency and obtainable detection limits. The distance between the optical detection window and the sprayer tip was minimized by placing the optical cell directly in front of the electrospray interface. Similar separation efficiencies for both detection modes could thus be obtained. No significant peak-broadening induced by the MS interface was observed. The high fluorescence quantum yield and the high proton affinity of the model analytes investigated resulted in limits of detection in the fg (nmol/L) range for both detection methods. The analysis of confiscated ayahuasca samples and ethanolic plant extracts revealed complementary selectivities for LIF and MS detection. Thus, it is possible to improve peak identification of the solutes investigated by the use of these two detection principles.     

Origins of stereoselectivity in the oxido-alkylidenation of alkynes

A mild, convenient oxido-alkylidenation of alkynes is described. The three-step sequence involves the 1,3-dipolar cycloaddition of a nitrone and an alkynoate, oxidation of the resulting isoxazoline, and stereoselective extrusion of nitrosomethane. Quantum mechanical calculations identified the interactions of R3 with the oxidant and the preferred conformation of a diradical intermediate as major factors controlling the stereoselectivity of the oxidation and torquoselectivity of the extrusion.     

Filmströmungen bei sich überlagernden Einflüssen

Zusammenfassung Es wird eine einheitliche Untersuchungsmet-hode für Filmströmungen beschrieben. Damit können sehr gut die Bereiche mit Überlagerung von verschiedenen Einflüssen, z. B. laminarer und turbulenter Transport, Schwerkraft und Reibungskraft an der Filmoberfläche, Phasenübergang (Filmkondensation oder Verdampfung) und Änderung der Filmtemperatur (Kühlung oder Erwärmung), untersucht werden. Die Ergebnisse sind in Diagrammen dargestellt und werden mit Versuchswerten verglichen. Für die Berechnung des Kräfteverhältnisses, der Filmdicke und des Wärmeübergangskoeffizienten werden für die Praxis geeignete Beziehungen vorgeschlagen.

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Film flow with superposition of various effects

An uniform method of analysis for film flow will be given. By this the regions with superposition of various effects can be investigated very well, for instance laminar and turbulent transport, gravity and frictional force on the film surface, phase transition (film condensation or evaporation) and variation of film temperature (cooling or heating). The results are given in diagrams and compared with experimental data. Practicably suitable equations will be proposed for determining of ratio of force, film thickness and heat transfer coefficient.

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Formelzeichen B benetzte Breite - c _P spez. Wärmekapazität - D Rohrdurchmesser - g Erdbeschleunigung - h _V Verdampfungsenthalpie - l Länge - Bezugsgröße (siehe Gl. (12)) - m/A Massenstromdichte - Pr Prandtl-Zahl - q Wärmestromdichte - q _p ⁺ Parameter für Wärmestromdichteverteilung - Re _F Reynolds-Zahl für Film - T, t Temperatur - u Geschwindigkeit - u Schubspannungsgeschwindigkeit - x Dampfanteil - y Wandabstand - Wärmeübergangskoeffizient - Rohr- bzw. Plattenneigung - Filmdicke - dynamische Zähigkeit - Wärmeleitkoeffizient - kinematische Zähigkeit - Dichte - Schubspannung - _p ⁺ Schubspannungsparameter bei Abwärtsströmung - _w ⁺ Schubspannungsparameter bei Aufwärtsströmung - dimensionsloser Wandabstand Indizes BS Blasensieden - F Film - f flüssig - g gas- bzw. dampfförmig - L Längsrichtung - l laminar - m mittlere - P Phasengrenze - S Siedezustand - t turbulent - ü Übergang - W Wand - x örtlich     

Calibration-free concentration determination of charged colloidal nanoparticles and determination of effective charges by capillary isotachophoresis

Although colloidal nanoparticles show an electrophoretic heterogeneity under the conditions of capillary electrophoresis, which can be either due to the particle-size distribution and/or the particle shape distribution and/or the zeta-potential distribution, they can form correct isotachophoretic zones with sharp-moving boundaries. Therefore, the technique of isotachophoresis permits to generate plugs in which the co-ions and counter ions of the original colloidal solution are removed and replaced by the buffering counter ions of the leading electrolyte. It is shown that analytical isotachophoresis can be used to measure directly, without calibration, the molar (particle) concentration of dispersed ionic colloids provided that the transference number and the mean effective charge number of the particles (within the isotachophoretic zone) can be determined with adequate accuracy. The method can also be used to measure directly the effective charge number of biomacromolecules or colloidal particles, if solutions with known molar (particle) concentration can be prepared. The validity of the approach was confirmed for a model solution containing a known molar concentration of bovine serum albumin.      

Average case complexity results for a centering algorithm for linear programming problems under Gaussian distributions

To solve linear programming problems by interior point methods an approximately centered interior point has to be known. Such a point can be found by an algorithmic approach – a so-called phase 1 algorithm or centering algorithm. For random linear programming problems distributed according to the rotation symmetry model, especially with normal distribution, we present probabilistic results on the quality of the origin as starting point and the average number of steps of a centering algorithm.     

Nonaqueous capillary electrophoresis-mass spectrometry: a versatile, straightforward tool for the analysis of alkaloids from psychoactive plant extracts

In this study we show that a nonaqueous capillary electrophoresis mass spectrometry (NACE-MS) method carefully optimized by a design of experiment can be applied to a very large number of alkaloids in different plant extracts. It is possible to characterize the pattern of the psychoactive alkaloids in several plant samples and preparations thereof, each presenting different challenges in their analysis. The method is shown to be able to separate structurally closely related substances, diastereomers and further isobaric compounds, to separate members of different alkaloid classes within one run and to tolerate significant matrix load. A comparison with methods presented in the literature reveals that a near-generic NACE-MS method for the fast profiling of alkaloids in forensically relevant plant samples has been developed.