Microwave-assisted Extraction (MAE)-acid Hydrolysis of Dithiocarbamates for Trace Analysis in Tobacco and Peaches

A simple and rapid method is presented for the analysis of residues of ethylenebis(dithiocarbamate) (maneb, zineb, and mancozeb) and N,N-dimethyldithiocarbamate (thiram and ziram) fungicides in dry tobacco leaves and peaches. Residues are extracted and hydrolyzed to CS(2) in a single step by use of microwave energy in a closed-vessel system while the evolved CS(2) trapped in a layer of iso-octane overlaying the reaction mixture is taken for gas chromatographic-flame photometric analysis. This combined extraction-hydrolysis step is carried out in 10 and 15 min for sets of 12 samples of tobacco and peach matrices, respectively. Total sample preparation time for GC analysis is 40 min. The limits of detection (LOD) are 0.005 mg/kg for thiram and ziram on peaches and 0.1 mg/kg for maneb, zineb, and mancozeb on tobacco. The respective LOD and limit of quantification (LOQ) levels in CS(2) equivalents are 0.003 and 0.006 mg/kg on peaches and 0.04 and 0.2 mg/kg on tobacco, respectively. Recoveries in the 0.01-60 mg/kg fortification range are 80-100% with respective relative standard deviations <20%. The method was used for the analysis of >3000 commercial tobacco samples including also different marketed cigarette brands.