1. Department of Chemistry, University of Modena and Reggio Emilia, via G. Campi 183, 41100 Modena, Italy; Department of Agricultural Sciences, University of Modena and Reggio Emilia, via J. F. Kennedy 17, 42100 Reggio Emilia, Italy; and Ispettorato Centrale Repressione Frodi, via J. Cavedone 29, 41100 Modena, Italy