1. Instrumental Analytical Chemistry, University of Duisburg-Essen, Universitätsstr. 5, 45141 Essen, Germany
2. Centre for Water and Environmental Research (ZWU), University of Duisburg-Essen, Universitätsstr. 2, 45141 Essen, Germany
3. IWW Water Center, Moritzstr. 26, 45476 Mülheim an der Ruhr, Germany