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The detection of hydrogen sulfide (H2S) by 2 + 1 resonance-enhanced multi-photon ionization (REMPI) and the application of H2S as a laser dopant for the detection of polar compounds in laser ion mobility (IM) spectrometry at atmospheric pressure were investigated. Underlying ionization mechanisms were elucidated by additional studies employing a drift cell interfaced to a time-of-flight mass spectrometer. Depending on the pressure, the primary ions H2S+, HS+, S+, and secondary ions, such as H3S+, were observed. The 2 + 1 REMPI spectrum of H2S near lambda = 302.5 nm was recorded at atmospheric pressure. Furthermore, the limit of detection and the linear range were established. In the second part of the work, H2S was investigated as an H2O analogous laser dopant for the ionization of polar substances by proton transfer. H2S exhibits a proton affinity (PA) similar to that of H2O, but a significantly lower ionization energy facilitating laser ionization. Ion-molecule reactions (IMR) of H3S+ with a variety of polar substances with PA between 754.6 and 841.6 kJ/mol were investigated. Representatives of different compound classes, including alcohols, ketones, esters, and nitroaromatics were analyzed. The IM spectra resulting from IMR of H3S+ and H3O+ with these substances are similar in structure, i.e., protonated monomer and dimer ion peaks are found depending on the analyte concentration.
Laser-based ion mobility (IM) spectrometry was used for the detection of neuroleptics and PAH. A gas chromatograph was connected to the IM spectrometer in order to investigate compounds with low vapour pressure. The substances were ionized by resonant two-photon ionization at the wavelengths lambda = 213 and 266 nm and pulse energies between 50 and 300 mu J. Ion mobilities, linear ranges, limits of detection and response factors are reported. Limits of detection for the substances are in the range of 1-50 fmol. Additionally, the mechanism of laser ionization at atmospheric pressure was investigated. First, the primary product ions were determined by a laser-based time-of-flight mass spectrometer with effusive sample introduction. Then, a combination of a laser-based IM spectrometer and an ion trap mass spectrometer was developed and characterized to elucidate secondary ion-molecule reactions that can occur at atmospheric pressure. Some substances, namely naphthalene, anthracene, promazine and thioridazine, could be detected as primary ions (radical cations), while other substances, in particular acridine, phenothiazine and chlorprothixene, are detected as secondary ions (protonated molecules). The results are interpreted on the basis of quantum chemical calculations, and an ionization mechanism is proposed.
Pestizideinsatz gegen die Rosskastanien-Miniermotte (Cameraria ohridella) im Stadtgebiet Potsdam
(2005)
In Deutschland hat sich in den letzten zehn Jahren die aus dem Balkan eingewanderte Rosskastanien-Miniermotte verbreitet; sie richtet vor allem in Ballungsgebieten an der weiß blühenden Rosskastanie starke Schäden an. Neben der vollständigen mechanischen Beseitigung und Entsorgung des Falllaubes im Herbst eignen sich zur Bekämpfung chemische Pflanzenschutzmittel. In Potsdam sind 2001 und 2003 an zwei Standorten befallene Rosskastanien versuchsweise mit zwei unterschiedlichen Pestiziden erfolgreich behandelt worden. 2005 wurden die Standorte beprobt und die Bodenproben auf Rückstände der verwendeten Mittel untersucht. TerraTech möchte Kommunen mit vergleichbarem Problem Hinweise auf Bekämpfungsmethoden geben, veröffentlicht diesen Beitrag aber vor allem unter dem Gesichtspunkt des Boden- und Grundwasserschutzes.