Solution mixing and the emission of light in flow-cells for chemiluminescence detection

Constructing flow-through reactors for chemiluminescence detection by machining channels into polymer disks has enabled the exploration of new configurations and materials that can improve signal intensity beyond that attainable with the traditional coiled-tubing design. Several approaches to merge reactant solutions were examined: an intersection, chamber or deeper well in the centre of a serpentine configuration flow-cell (directly in front of a photomultiplier tube), or a confluence point outside the detection zone. For several analytically useful, rapid chemiluminescence reactions, the single-inlet flow-cell with external Y-piece was most suitable, but for others (such as KMnO(4)/Mn(II) with morphine, and [Ir(f-ppy)(2)BPS](-) with fluoroquinolones) the dual-inlet configuration provided greater signals. The introduction of central mixing zones with larger widths than the channel reduced the chemiluminescence response. The reversing turns of a serpentine channel promote efficient mixing and greater chemiluminescence intensities than a spiral channel, but increasing the sharpness of the turns created areas of poor solution flow and decreased the chemiluminescence response. Teflon disks impregnated with glass microspheres increased the chemiluminescence signals by 13%-17%, due to the greater reflection of stray light towards the photodetector.     

Monitoring sea lamprey pheromones and their degradation using rapid stream‐side extraction coupled with UPLC‐MS/MS

Pheromones guide adult sea lamprey (Petromyzon marinus) to suitable spawning streams and mates, and therefore, when quantified, can be used to assess population size and guide management. Here, we present an efficient sample preparation method where 100 mL of river water was spiked with deuterated pheromone as an internal standard and underwent rapid field‐based SPE and elution in the field. The combination of field extraction with laboratory UPLC‐MS/MS reduced the sample consumption from 1 to 0.1 L, decreased the sample process time from more than 1 h to 10 min, and increased the precision and accuracy. The sensitivity was improved more than one order of magnitude compared with the previous method. The influences of experimental conditions were assessed to optimize the separation and peak shapes. The analytical method has been validated by studies of stability, selectivity, precision, and linearity and by the determination of the limits of detection and quantification. The method was used to quantify pheromone concentration from five streams tributary to Lake Ontario and to estimate that the environmental half‐life of 3kPZS is about 26 h.     

Saturation of gyrokinetic turbulence through damped eigenmodes

In the context of toroidal gyrokinetic simulations, it is shown that a hierarchy of damped modes is excited in the nonlinear turbulent state. These modes exist at the same spatial scales as the unstable eigenmodes that drive the turbulence. The larger amplitude subdominant modes are weakly damped and exhibit smooth, large-scale structure in velocity space and in the direction parallel to the magnetic field. Modes with increasingly fine-scale structure are excited to decreasing amplitudes. In aggregate, damped modes define a potent energy sink. This leads to an overlap of the spatial scales of energy injection and peak dissipation, a feature that is in contrast with more traditional turbulent systems.     

A Coordination Compound of Ge0 Stabilized by a Diiminopyridine Ligand

Reduction of the cationic Ge^II complex [dimpyrGeCl][GeCl₃] (dimpyr=2,6‐(ArN=CMe)₂NC₅H_3, Ar=2,6‐iPr₂C₆H₃) with potassium graphite in benzene affords an air sensitive, dark green compound of Ge⁰, [dimpyrGe], which is stabilized by a bis(imino)pyridine platform. This compound is the first example of a complex of a zero‐valent Group 14 element that does not contain a carbene or carbenoid ligand. This species has a singlet ground state. DFT studies revealed partial delocalization of one of the Ge lone pairs over the π*(C?N) orbitals of the imines. This delocalization results in a partial multiple‐bond character between the Ge atom and imine nitrogen atoms, a fact supported by the X‐ray crystallography and IR spectroscopy data.     

Comprehensive sample analysis using high performance liquid chromatography with multi-detection

Herein we assess the separation space offered by a liquid chromatography system with an optimised uni-dimensional separation for the determination of the key chemical entities in the highly complex matrix of a tobacco leaf extract. Multiple modes of detection, including UV–visible absorbance, chemiluminescence (acidic potassium permanganate, manganese(IV), and tris(2,2′-bipyridine)ruthenium(III)), mass spectrometry and DPPH radical scavenging were used in an attempt to systematically reduce the data complexity of the sample whilst obtaining a greater degree of molecule-specific information. A large amount of chemical data was obtained, but several limitations in the ability to assign detector responses to particular compounds, even with the aid of complementary detection systems, were observed. Thirty-three compounds were detected via MS on the tobacco extract and 12 out of 32 compounds gave a peak height ratio (PHR) greater than 0.33 on one or more detectors. This paper serves as a case study of these limitations, illustrating why multidimensional chromatography is an important consideration when developing a comprehensive chemical detection system.     

The early Weyl universe

The consequences of a period of Weyl invariance in the early universe are investigated. It is argued that the natural outcome of such a period is a Kaluza-Klein style compactification of an internal space in which any time variation of the scale factor of this space is absorbed (via a Weyl transformation) into the gravitational coupling. A five-dimensional test model is shown to undergo exponential inflation of the space-time sector due to a false vacuum state of the non-metric part of the connection.     

Particularist semantic normativity

We sketch the view we call contextual semantics. It asserts that truth is semantically correct affirmability under contextually variable semantic standards, that truth is frequently an indirect form of correspondence between thought/language and the world, and that many Quinean commitments are not genuine ontological commitments. We argue that contextualist semantics fits very naturally with the view that the pertinent semantic standards are particularist rather than being systematizable as exceptionless general principles.     

On the Volume of 4-Cycle Trades

 A 4-cycle trade of volume t corresponds to a simple graph G without isolated vertices, where the edge set can be partitioned into t 4-cycles in at least two different ways such that the two collections of 4-cycles have no 4-cycles in common. The foundation of the trade is v=|V(G)|. This paper determines for which values of t and v there exists a 4-cycle trade of volume t and foundation v. Received: September 16, 2000 Final version received: October 2, 2001