Determination of ethanol in ionic liquids using headspace solid-phase microextraction–gas chromatography

The application of ionic liquids (ILs) as nonderivatizing solvents for the pretreatment and regeneration of cellulose is a growing area of research. Here we report the development of a rapid and simple method for the determination of residual ethanol content in two hydrophilic ILs, 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium acetate. The method utilizes headspace solid-phase microextraction coupled with gas chromatography at elevated extraction temperatures, resulting in rapid equilibration times. The effect of IL water content on the ethanol extraction efficiency is presented. Recovery experiments carried out in real samples gave recoveries ranging from 96.8 to 98.2%.     

Final results from phase II of the Mainz neutrino mass searchin tritium {\beta} decay

This paper reports on the improved Mainz experiment on tritium spectroscopy which yields a 10 times higher signal to background ratio than before. The main experimental effects and systematic uncertainties have been investigated in side experiments, and possible error sources have been eliminated. Extensive data taking took place in the years 1997 to 2001. A residual analysis of the data sets yields for the square of the electron antineutrino mass the final result of eV²/c⁴. We derive an upper limit of eV/c² at 95% confidence level for the mass itself.Received: 21 December 2004, Published online: 9 March 2005PACS: 1460.Pq, 23.40.-s, 2930.Dn, 2930.AjCh. Kraus: Present address: Department of physics, Queens university, K7L3N6 Kingston, CanadaB. Bornschein: Present address: Forschungszentrum Karlsruhe, Tritiumlabor, 76344 Eggenstein-Leopoldshafen, GermanyL. Bornschein: Present address: Universität Karlsruhe (TH), Institut für exp. Kernphysik, Postfach 6980, 76128 Karlsruhe, GermanyA. Kovalik: On leave from the Nuclear Physics Institute of the Acad. Sci. Czech Republic, 25068 Rez near PragueB. Ostrick: Present address: Helmholtz-Institut für Strahlen und Kernphysik, Universität Bonn, 53115 Bonn, Germany Corresponding author: E.W. OttenCh. Weinheimer: Present address: Institut für Kernphysik, Universität Münster, 48149 Münster, GermanyThis paper comprises principal parts of the PhD theses of Christine Kraus, Beate Bornschein and Lutz Bornschein.     

A two-step mimic for direct, asymmetric bromonium- and chloronium-induced polyene cyclizations

Although direct, asymmetric, halonium-induced cyclizations have proven difficult to achieve in the absence of enzymes, this report provides a two-step alternative based on reacting polyenes with chiral mercury(II) complexes to afford a number of polycyclic organomercurials that can be subsequently converted, with retention, into their corresponding chlorine, bromine, and iodine derivatives in good yield and enantioselectivity. A five-step asymmetric total synthesis of the natural product 4-isocymobarbatol is also described.     

Detection of hydrogen-bonded adenine-thymine base-pair complexes by electrospray mass spectrometry

Abstract

Bibracchial lariat ether compounds having three-carbon sidearms terminated in either adenine or thymine have the potential to form a molecular box in which the “ends” are crown ethers and the “sides” are hydrogen-bonded base pairs. Previous solution studies relying upon NMR and vapor pressure osmometry confirmed the formation of complexes. In the present study, four diaza-18-crown-6 derivatives having either one or two sidearms each terminated in either adenine or thymine have been studied in a mixture of CHCl₃ and CH₃OH. Either acetic acid or sodium chloride was added to the solutions. For the two-armed systems, the preferred complex was the dimer involving adenines on one monomer and thymines on the other. Homodimers and other complexes were detected as well. The preferred single-armed complex was that occurring between the monomer whose sidearm was terminated in thymine and either H⁺ or Na⁺.     

Biogenic volatile organoiodine and organobromine hydrocarbons in the Atlantic Ocean from 42°N to 72°S

During the cruise ANT X/1 and 2 of the research vessel Polarstern from November 1991 to March 1992, 39 surface water samples of the Atlantic Ocean from 42°N to 72.5°S were collected and analysed for their concentration of volatile iodinated and brominated hydrocarbons. The concentration of chlorophyll-a was used as an indicator for phytoplankton, which is one of the main producers of iodinated and brominated compounds in the ocean. For determination of chlorophyll-a, fluorescence spectroscopy was applied, whereas the measurement of halogenated volatile hydrocarbons was carried out by a purge and trap system with subsequent gas chromatographic separation and detection by an electron capture detector. With this technique the brominated substances CHBr₃, CH₂Br₂, CHBr₂Cl and CHBrCl₂ have been detected in the range of <0.03?ng/L to 15?ng/L. For these volatile bromomethanes a distinct concentration profile was found. CHBr₃ was always found to be the substance with the highest concentration followed by CH₂Br₂, CHBr₂Cl and CHBrCl₂. It could also be shown that in addition to CH₃I, which for a long time was believed to be the only volatile iodinated substance in the marine environment, other iodinated substances like CH₂ClI, CH₂I₂ and CH₃CH₂CH₂I exist in the range of <0.01?ng/L to 2.2?ng/L in surface water of the Atlantic Ocean. Although it is improbable that chlorophyll-a is directly involved in the marine production of halogenated hydrocarbons, it was found that it could be used as an indicator for the biogenic formation of brominated compounds, whereas the correlation between chlorophyll-a and the iodinated substances was not of the same quality. The positive correlation between bromoform and dibromomethane proves the same biogenic origin and mechanism of formation, which could not be found for the different iodinated compounds.     

Long-range strain correlations in sheared colloidal glasses

Glasses behave as solids on experimental time scales due to their slow relaxation. Growing dynamic length scales due to cooperative motion of particles are believed to be central to this slow response. For quiescent glasses, however, the size of the cooperatively rearranging regions has never been observed to exceed a few particle diameters, and the observation of long-range correlations has remained elusive. Here, we provide direct experimental evidence of long-range correlations during the deformation of a dense colloidal glass. By imposing an external stress, we force structural rearrangements, and we identify long-range correlations in the fluctuations of microscopic strain and elucidate their scaling and spatial symmetry. The applied shear induces a transition from homogeneous to inhomogeneous flow at a critical shear rate, and we investigate the role of strain correlations in this transition.     

Design of polarization-maintaining retro-reflector for folded-path applications

A design of polarization-maintaining retro-reflectors(PMRRs) for folded-path applications is proposed and analyzed.The prism-based scheme enables the output light,which is parallel to the input,to have an identical state of polarization.The principle of the design is theoretically verified,and the related error is analyzed due to possible manufacturing imperfection.The maximum spatial angle error is ±2.75°.The effect on the extinction ratio and insertion loss is also discussed,which further proves the design’s feasibility in practical applications.     

关于n+k相多体系(k≥4)封闭网的构造

本文证明了n+k多体系(k≥4)的全部可能的封闭网均可以通过若干相应的子n+3相多体系的拼合运算得出,从而为具体构造n+k相多体系(k≥4)的全部合理的封闭网,提供了基本方法。