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.     

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.     

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.     

Indirect CE‐UV detection for the characterization of organic and inorganic ions of a broad mobility and pKa range in engine coolants

An alternative CE‐(indirect ultraviolet) method for the analysis of inorganic and organic anions in ethylene glycol‐based engine coolants is presented using a BGE with 4 mM pyromellitic acid and 3.4 mM 1,6‐hexamethylene diamine, pH 3. Baseline separation of six inorganic (e.g. nitrite, nitrate, and sulfate) and five organic anions (e.g. acetic and glycolic acid) was achieved. Quantification of 8 out of 11 specified anions was possible in stressed engine coolant samples after simple aqueous dilution. LODs between 0.8 and 15.1 mg/L with RSD values of peak areas between 2.6 and 11.9% were obtained. Some limitations due to matrix effects can be overcome with slight adaptations of the BGE. The flexibility of the method is vital regarding the increasing demands for the composition of engine coolants for pollution reduction.     

Geodesic-Planar Conjugates: Substituted Buckybowls—Synthesis,Photoluminescence and Electrochemistry

C−C cross coupling products of bowl-shaped as-indaceno[3,2,1,8,7,6-pqrstuv]picene (Idpc) and different planar arenes and ethynyl-arenes were synthesized. Photoluminescence as well as electrochemical properties of all products were investigated and complemented by time-dependent quantum chemical calculations. UV/Vis spectroelectrochemistry investigations of the directly linked (Idpc)₂ indicated the absence of any intramolecular charge-transfer transition of intermittently formed (Idpc)₂^.−. All coupling products showed fluorescence. Ferrocene-1-yl-Idpc was structurally characterized by X-ray diffraction and is a rare example of a ferrocene-containing buckybowl exhibiting luminescence.     

Capillary electrophoresis applied for the determination of acidity constants and limiting electrophoretic mobilities of ionizable herbicides including glyphosate and its metabolites and for their simultaneous separation

Thermodynamic acidity constants and limiting ionic mobilities were determined for polyprotic non-chromophore analytes using capillary electrophoresis with capacitively coupled contactless conductivity detection. It was not necessary to work with buffers of identical ionic strength as ionic strength effects on effective electrophoretic mobilities were corrected by modeling during data evaluation (software AnglerFish). The mobility data from capillary electrophoresis coupled to conductivity detection were determined in the pH range from 1.25 to 12.02 with a high resolution (36 pH steps). With this strategy, thermodynamic acidity constants and limiting ionic mobilities for various acidic herbicides were determined, sometimes for the first time. The model analytes included glyphosate, its metabolites, and its acetylated derivates (aminomethyl phosphonic acid, glyoxylic acid, sarcosine, glycine, N-acetyl glyphosate, N-acetyl aminomethyl phosphonic acid, hydroxymethyl phosphonic acid). The obtained data were used in simulations to optimize separations by capillary electrophoresis. Simulations correlated very well to experimental results. With the new method, the separation of glyphosate from interfering components like phosphate in beer samples was possible.     

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