Determination of ETU in tomatoes and tomato products by HPLC-PDA: evaluation of cleanup procedures

An HPLC-PDA method for the determination of ethylenethiourea (ETU), the main degradation product of the organic fungicides ethylene bis(dithiocarbamate)s (EBDCs), in tomatoes and tomato products is reported. Solid-matrix liquid-liquid (l-l) partitioning and separatory funnel l-l partitioning for the cleanup were examined. The effect of salt addition, pH, and phase ratio on analyte recovery at the cleanup step was studied. It was found that solid-matrix l-l partitioning afforded higher precision and more selective separation of the analyte. According to the method proposed, the samples were extracted with methanol/water (3:1, v/v) and cleaned up on an Extrelut 20 column. ETU was eluted with dichloromethane and separated on a reversed phase HPLC column. For tomato products with degrees Brix > 20 further purification through silica cartridge was adopted. The method was validated over the following ranges of concentrations: 0.01-0.5 mg/kg for tomatoes, 0.01-0.1 mg/kg for tomato juice, and 0.05-0.25 mg/kg for tomato paste. The accuracy (recoveries > 70%) and the precision obtained (%RSD < 10%) were satisfactory.