Analysis of dithiocarbamates in berries and leafy vegetables by ultra-high performance liquid chromatography coupled with tandem mass spectrometry

Abstract

A sensitive method has been developed for the analysis of the three subclasses of dithiocarbamates (DTCs), (dimethyl dithiocarbamates (DMDs), ethylenebisdithiocarbamates (EBDs), propylenebisdithiocarbamates (PBD)) in berries and leafy vegetables using UHPLC/MS-MS. DTCs were extracted by first decomplexing metal ions using an alkaline solution (pH 9.8) of cysteine-EDTA. The second step was the methylation of the dithiocarbamic acids formed by dimethyl sulfate in acetonitrile to obtain the methylated dithiocarbamates. The method was validated using ziram, zineb, and propineb to represent DMDs, EBDs, and PBDs, respectively. In addition, spinach and blueberries were used as representative matrices for leafy vegetables and berries, respectively. The average recovery obtained ranged from 71.8% to 92.2% for methyl dimethyldithiocarbamate (DMD-Me) with an inter-day precision of 4.7% to 12.2%; from 30.8% to 62.2% for dimethyl ethylenebisdithiocarbamate (EBD-Me) with an inter-day precision of 4.5% to 8.9%. For dimethylpropylene bisdithiocarbamate (PBD-Me), they ranged from 6.3% to 8.2% with an inter-day precision of 0.8% to 1.1%. The limits of quantification (LOQ) expressed in µg/kg of carbon disulfide (CS2) were low in berries and leafy vegetables, ranging from 0.14 µg/kg to 0.27 µg/kg for DMDs, 0.87 µg/kg to 1.27 µg/kg for EBDs, and 0.03 µg/kg for PBDs. Analysis of 51 samples showed the presence of DMDs and EBDs in 96% of them, and 99% of these contained propineb. Furthermore, none of the concentrations detected in these samples exceeded the maximum residue limits (MRLs) set by the European Union, except for propineb, as its MRL has been lowered to the LOQ.