Abstract
A multi-residue method for simultaneous determination of 41 LC-amenable pesticides in rice, belonging to different chemical classes has been developed in Iran by LC-MS/MS. For the first time the pesticides were analyzed simultaneously in a single run using positive electrospray ionization with multiple reaction monitoring (MRM) after extraction with slightly modified QuEChERS method. The calibration curve for each analyte was linear over the concentration range of 0.02-1.0 μg/g with a correlation coefficient range between 0.993 and 0.999. The LOQ and LOD were .025 μg/g and 0.008 μg/g respectively, for all 41 pesticides and the mean recoveries obtained for three fortification levels (0.025, 0.08 and 0.250 μg/g) were 71-119% with satisfactory precision (RSD<20%). The developed method was used to investigate the occurrence of pesticides in 30 domestic and 30 imported rice samples collected from Tehran market. Five compounds were detected in 11 domestic and 9 imported positive samples in concentration range from 0.032 μg/g to 0.081 μg/g and 0.028 μg/g to 0.074 μg/g, respectively. With the exception of prohibited pesticides, phosphamidon and TCMTB, three permitted pesticides, cinosulfuron, triadimenol and tricyclazole, found in positive rice samples were below MRLs established by Institute of Standards and Industrial Research of Iran (ISIRI).