Simultaneous Determination of Trichlorfon and Dichlorvos Residuesin Olive Flounder (Paralichthys olivaceus) by Liquid Chromatography-Mass Spectrometry: Validation and Application to Pharmacokinetics

Trichlorfon, an organophosphate insecticide, is used in aquaculture to control parasitic organisms. This study evaluated a rapid, sensitive, and specific LC-MS/MS method for the determination of trichlorfon and dichlorvos residues in the tissues of olive flounder. Separation was carried out on an Eclipse Plus C18 column by gradient elution using wateracetonitrile with 0.1% formic acid at a flow rate of 0.3 mL min-1. Detection was performed by electrospray ionization in the positive ion mode with nitrogen as the collision gas. In multiple reaction monitoring (MRM) mode, ion transitions were detected at m/z 259→109 (trichlorfon) and m/z 221→108.9 (dichlorvos). Linear calibration curves were obtained with good correlation coefficients. The limit of detection (LOD) values for trichlorfon and dichlorvos were 0.5 and 1.2 μg kg-1, respectively, with corresponding limit of quantification (LOQ) values of 1.7 and 4.0 μg kg- 1, respectively. The average recoveries ranged from 88.2% to 114% at three spiked concentration levels (5, 10, and 100 μg L-1) with relative standard deviations (RSDs) below 13.8% for plasma, muscle, and liver. The developed analytical method was applied to pharmacokinetic studies of trichlorfon and dichlorvos in olive flounder after administration by dipping at concentrations of 1 or 5 mg kg-1.