New stationary phases of conjugated π-electron systems for HPLC—characterization of structure and dynamics by solid state NMR spectroscopy

Four new stationary phases for HPLC were prepared by modifying silica gel with a trifrnctional aminoalkyl silane. A conjugated π-electron system was linked to the amino group either directly or with a carboxylic anhydride as a spacer in between. Characterization and dynamic measurements of the new stationary phases were performed by solid state NMR spectroscopy. The results of the ²⁹si and ¹³C CP/MAS techniques were compared with the recently developed ¹H MAS-only technique. Despite strong homonuclear dipole-dipole interactions it was possible to obtain well resolved ¹H MAS spectra of those stationaru phases with a high degree of crosslinking. Limited mobility of the aromatic ligand fragments is common for all examined stationaryu phases. The chromatographic properties of the new phases were tested by their ability tio sepatate a mixture of eight PAHS. It could be shown that the π-π interaction mechanism is responsible for the separation of the eight PAHs, because the elution order of the PAHs did not changem despite the use of both a nonpolar mobile phase (n-heptane) and a polar mobile phase (methanol/ water mixture).     

A note on the positive solutions of second order differential equations

We obtain an existence theorem for monotone positive solutions of nonlinear second-order nonlinear differential equations via principal and nonprincipal solutions of the corresponding homogeneous equation.     

Liquid chromatography/tandem mass spectrometry for analysis of 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH) and 1,2,5,6-tetrabromocyclooctane (TBCO)

Although the two flame retardants 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH) and 1,2,5,6-tetrabromocyclooctane (TBCO) have been widely used, a selective instrumental method of analysis for these compounds has not been developed to date. In this study, we demonstrate the feasibility to utilize liquid chromatography/tandem mass spectrometry (LC/MS/MS) for the separation and analysis of α- and β-TBCO and α-, β-, γ-, and δ-TBECH. Acetone was initially used in a tetrahedron solvent system for LC optimization. A simple isocratic elution allowed near-baseline separation of these compounds. Different ionization approaches and mechanisms were investigated. The mass spectrometric transition of [M + O(2)](-) => Br(-) (459.8 => 78.9) was a selective detection method for the target analytes. Good instrument detection limits (5 pg for γ-/δ-TBECH, 125 pg for α-/β-TBECH, and 30 pg for α-/β-TBCO with 2.0 μL injection) were obtained. Excellent linearity up to 50 ng/μL (R(2) >0.999) was also achieved. This method has been applied to environmental samples (surface water) for screening purposes with recoveries ranging from 76-92% (CV%: 5-8%). This method shows significant improvement over previous methods.     

A micromanipulator for chemical analysis on the microgram scale

Summary A micromanipulator is described which has been specially designed to meet the requirements of chemical work on the microgram scale. The instrument carries a micropipette controlled by a micrometer syringe, and manipulates this in relation to the vessels, which are carried on the rotating mechanical stage of a low-power microscope.

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Zusammenfassung Ein Mikromanipulator für die speziellen Bedürfnisse der chemischen Untersuchung von Gammamengen wird beschrieben. Das Instrument trägt eine Mikropipette, die mit Hilfe einer Mikrometer-Injektionsbürette kontrolliert wird. Diese Pipette wird mittels des Manipulators in die Reaktionsgefäße eingeführt, die auf dem drehbaren Tisch eines Mikroskopes mit schwacher Vergrößerung angebracht werden.

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Résumé On décrit un micromanipulateur spécialement destiné à faire face aux besoins du travail chimique à l'échelle du microgramme. L'instrument porte une micropipette controlée par une seringue micrométrique et actionne celle-ci par rapport aux vases qui sont portés par la plateforme tournant mécaniquement d'un microscope de faible puissance.

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With 2 figures.