1. Department of Natural Sciences, Bonn-Rhein-Sieg University of Applied Sciences, von-Liebig-Strasse 20, D-53359 Rheinbach, Germany
2. Spectral Service AG, Emil-Hoffmann-Strasse 33, D-50996 Köln, Germany
3. Institute of Chemistry, Saratov State University, Astrakhanskaya Street 83, 410012 Saratov, Russia