2.5. Sample preparation

Calibrators and controls were prepared in drug-free plasma to compensate the matrix effect and treated in the same way as patient samples. A 10-μL aliquot of calibrator, control, or sample was transferred into a 1.5 mL centrifuge tube containing 500 μL of protein precipitation reagent. Each tube was vortexed and then centrifuged at 12,000 rpm for 15 min. To 1 mL of water was added 100 μL supernatant, and the solution was directly injected into UPLC-MS/MS.