[1] Univ Antwerp, Micro & Trace Anal Ctr, B-2610 Antwerp, Belgium
[2] Hungarian Acad Sci, Res Inst Solid State Phys & Opt, H-1525 Budapest, Hungary
[3] Eotvos Lorand Univ Sci, Dept Inorgan & Analyt Chem, H-1518 Budapest, Hungary
[4] Univ W Hungary, Inst Food Sci, H-9200 Mosonmagyarovar, Hungary
[5] Jozsef Fodor Natl Publ Hlth Ctr, Cent Chem Lab, H-1450 Budapest, Hungary