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Eingeladener Vortrag
- nein (94)
Neue Ergebnisse der HPLC/MALDI-TOF-MS - Kopplung zur Charakterisierung von synthetischen Polymeren
(1998)
The simultaneous analytical discrimination of spectrally very similar components with time- and wavelength-resolved fluorescence spectroscopy is demonstrated for the fluorescent probe BP(OH)2 and its complexes with the d10 metal ions CdII and ZnII in water. Whereas the absorption and emission spectra of the three components largely overlap the fluorescence lifetimes differ significantly. As a consequence, analyzing steady-state emission spectra of samples containing unknown amounts of both metal ions yields poor results for the analytical validity but the recording of fluorescence decay curves at different emission wavelengths improves the quality of the results drastically. The two techniques are compared in terms of goodness and analytical accuracy of the fit as well as analytical applicability.
The photophysical behavior of a newly synthesized aza crown-substituted boron-dipyrromethene (BDP) dye and its dimethylamino analogue were investigated with steady-state and time-resolved fluorometry and compared to a reference compound. In solvents more polar than hexane, excitation of the dyes leads to a fast charge transfer from the locally excited (LE) state to a weakly emissive charge-transfer (CT) state. The donor-substituted compounds show dual emission from the LE and CT state, both fluorescence quantum yields being low. The rate constant of excited-state charge separation, calculated from the global analysis of time-resolved emission data, was determined to 1.6 × 1011 s-1 in 1,4-dioxane. The crowned compound forms 1:1-complexes with various alkali and alkaline-earth metal ions, which exist as two conformers in solution. In these complexes, coordination of the cation to the nitrogen donor atom of the crown inhibits the charge-transfer process, leading to a cation-dependent enhancement of the LE emission and the fluorescence lifetimes by factors >103. This efficient "switching on" of the fluorescence renders the crowned BDP dye an extremely sensitive fluorescent probe for metal ions.
Datenbank CHEMSAFE
(1998)
Summary
Substances like alcohols, ethers and esters have recently gained in importance as solvents for paints and varnishes, for surface degreasing and cleaning. Furthermore, fluorinated hydrocarbons are used as refrigerants, replacing chlorofluorocarbons. Because reliable data were not available for most of these substances, measurements of explosion limits and limiting oxygen concentration (MOC) have been carried out by PTB (flammable liquids) and BAM (flammable gases).
The poster presents the results of the most recent measurements of MOC for ethanol, i-propanol, ethyl acetate, propyl formate, hexane and for gases as e.g. difluoroethane and methane. Explosion limits and limiting oxygen concentrations have been measured in mixtures with air under ambient conditions and at elevated temperatures according to the German standard DIN 51649.