Determination of chlorpyrifos and its metabolites in rat blood using liquid chromatography/electrospray ionization tandem mass spectrometry

A method has been developed to quantify chlorpyrifos (O,O-diethyl O-[3,5,6,-trichloro-2-pyridyl] phosphorothionate) and its metabolites chlorpyrifos-oxon (O,O-diethyl-O[3,5,6,trichloro-2-pyridyl] phosphate) and TCP (3,5,6,-trichloro-2-pyridinol) in rat blood by liquid chromatography/ electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS). Rat blood was treated by liquid-liquid extraction and the analytes were separated by gradient elution on an Agilent Zorbax Extended-C₈ column (2.0×150 mm, 5 μm). Chlorpyrifos and chlorpyrifos-oxon were detected in positive ion mode using multiple reaction monitoring (MRM). TCP was detected in negative ion mode using parent-to-parent transition monitoring.This method was validated and the specificity, linearity, limit of quantitation (LOQ), precision, accuracy, stability, and recoveries were determined. The method was then applied to determine the level of chlorpyrifos and its metabolites from rats exposed to a subcutaneous injection of 10 and 18 mg/kg.