GC-MS/MS Determination of Chlorpyrifos and Its Metabolite in Rice

GC-MS/MS was applied to the determination of chlorpyrifos and its metabolite 3,5,6-trichloro-2-hydroxy pyridine (TCP) in rice. Samples were extracted with acetonitrile which contained (φ) 1% HCl. The extract was treated by salting out and evaporated to near-dryness and the residue and dissolved with ethyl acetate. TCP was derivatized with N-methyl-N-tert-butyl trimethylsilyl trifluoroacetamide, and the derivatized product and chlorpyrifos were determined by GC-MS/MS. External standard calibration was adopted in the determination. Linear relationships between peak areas and mass concentrations of chlorpyrifos and TCP were obtained in the same range of 0.02-0.4 mg·L-1. Values of lower limit of determination (10S/N)were 0.5 μg·kg-1 for chlorpyrifos and 0.2 μg·kg-1 for TCP. Tests for recovery and precision were made by standard addition method at 3 different concentration levels, values of recovery found were in the ranges of 94.3%-111.9% and 95.1%-109.6% with values of RSD′s (n=5) in the ranges of 1.7%-4.0% and 3.1%-11.6% for chlorpyrifos and TCP respectively.