Stir Bar Sorptive Extraction (SBSE) in sample preparation from heterogeneous matrices: determination of pesticide residues in pear pulp at ppb (ng/g) level

Chlorpyriphos methyl, chlorpyriphos ethyl, chlorthalonil, parathion methyl, parathion ethyl, fenitrothion, f-endosulfan, g-endosulfan and tetradifon residues were analysed in pear pulp (an heterogeneous matrix) by extraction on polydimethylsiloxane (PDMS) stir bar (SBSE) followed by recovery through thermodesorption (TD) and cGC-MS analysis. The levels of pesticides ranged from 10 to 100 ng/g (ppb). The results were compared to those obtained by a conventional method, namely SPMD-SPE cGC-ECD analysis. Characteristic recoveries ranged from 23.9% for chlorthalonil to 82.6% for fenitrothion. Comparable repeatability and intermediate precision, and lower LOD and LOQ than those of the reference SPMD/SPE-cGC-ECD method were obtained for each pesticide. A series of experiments on pear pulps and pear pulp liquid phase investigated the distribution of the pesticides between the solid and liquid phases and the influence of the ionic strength (salting and pH) on recovery.