Frozen plasma was thawed at 37 °C and centrifuged at 3000 rpm for 8 min to remove clots and the supernatant was used in the experiment. The pH of the plasma was recorded and only pH range between 7.4 and 8 was used. The plasma and compounds solution was pre-warmed to 37 °C. 10 µl prewarmed testing compound or reference compound (procaine) solution (20 µM in 0.05 mM sodium phosphate buffer (pH7.4) with 0.5% BSA) was mixed with 90 µl of plasma at different time points to allow for 5, 15, 30, 45, and 60 min of incubation time. For 0 min, the plasma was mixed with vehicle only. Acetonitrile was added to the compound and plasma mixture to quench the reaction and the resulting mixture was centrifuged (5594 g for 15 min). The supernatant was taken and diluted before LC-MS analysis.